Top Ten Coolest Physics Concepts in Life

This year in Physics, I went through many hard units where I was unable to grasp the material the way I should have been. But eventually, I was able to understand it and even had a few Eureka! moments. What helped me the most was when I was able to see and understand physics in real life.

1. Newton's First Law
An object in motion will stay in motion if no other force acts on it, and an object not in motion will not move unless an outside force acts on the object. The way I understood this concept was with the example of a coffee mug on the back of a car. The coffee mug is not moving, just chilln' on the back trunk. It wants to stay that way because its too lazy to move. But, there is an outside force that acts on it: the car starts to move forward. When the car moves forward the coffee mug simply falls off because instead of moving with the car, it  continues to not be in motion while the car moves. This is the coffee mugs inertia.

2. Tides
After learning about tides, we were let out for Christmas break, and I took a trip to the Maldives. Here, I saw the concept of tides all around me (literally all around me, the island was only 500 m both ways). The tides change 4 times a day because the earth is rotating and all parts of the earth are either feeling the attracting, or not feeling it, towards the moon. This is why opposite sides of the earth feel it at the same time: They are aligned with the direct force from the moon, therefore the water becomes concentrated in those sides, while the sides of the earth that don't feel the force, have low tide.

3. Newton's Third Law
His third law states that for every action there is an equal and opposite reaction. I saw this in my own life during this soccer season. When I went to shoot a goal, I was not only kicking the ball and because it was put in motion, was forced to move. The force went both ways: foot hits ball, ball hits foot. While learning about Newton's third law, we learned about how a horse and carriage works. We knew that for every action there is an equal and opposite reaction, so we could conclude that both the horse and carriage pull each other with equal forces. The reason the horse and carriage are able to move forward is because the horse pushes the ground harder than the carriage does. 

4. Electromagnetic Induction
The way we learned about this was through a real life example of a car at a stop light. Below the surface of the road is a coil of wire right before the intersection that is connected to the light. A car has a large magnet, so when the car pulls up to the intersection, it moves over the coil of wire. This causes the magnetic field to change. this change induces a voltage which causes a current. This current send the single up to the light to change. Electromagnetic induction is seen all over in everyday situations, such as airpower security detectors, electric guitars and credit card machines. 

5. Acceleration 
Objects are accelerating all the time while moving. Acceleration is the change in velocity over time. Acceleration is measured in m/s^2. We see acceleration in cars especially. How fast they are getting faster or how fast the are getting slower. When a skydiver jumps out of a plane, gravity accelerates the diver at 10m/s^2. What I struggled with the most was that there can be an increasing speed but a decreasing acceleration. This just means that an object might still be accelerating, but it is just getting faster slower. 

6. Center of Gravity
I saw this physics concept is many sports such as football and wrestling. To keep from being knocked over in football, the players keep their legs shoulder width apart. They do this because when they open their stance, they are widening their base of support. Then someone has a wide base of support, they're harder to knock over because to do so, their center of gravity would have to be moved over their base of support. These two boxes will fall over because their center of gravity is outside their base of support.

7. Rotational Velocity
Ice skaters have mastered the idea of rotational inertia in physics. They begin to spin with their legs and arms away from their axis of rotation. When they do this though, they have a small velocity. They then bring their arms and legs into their body, and their velocity increases. This is because they brought their mass closer into their axis of rotation. this can be shown in the picture to the left where the ice skater brings her arms in from being far away, and her velocity increases.


8. Lightning/Rods
Being from Saudi Arabia, we don't really have rain or lightning storms often, but when I came to the US, I saw metal rods next to structures. In physics I discovered that lightning rods help protect objects from being struck by lightning. Lighting takes the path of least resistance to get to the ground because of the clouds negative charge and the earth's surface being positively charged. When the lightning rod is along side your house, the lighting is attracted to the rod instead of your house. Because the rod is higher up and metal, this is the path of least resistance, therefore the lighting takes it. The odd provides a direct path to the ground, and lets the electricity to be grounded.

9. Transformers
Transformers can be seen everywhere: computer charger, in cars, basically anything that needs electricity. A transformer has two parts: primary and secondary coils. The current running through the transformer is AC current because the current must be moving back and forth across the coils to induce a voltage which causes a current. In the coil of wire, increasing the amount of coils will increase the voltage and current and visa versa. To convert the voltage from the wall to your computer, which must go from a lot of voltage to a little, there must be a transformer.

10. Vectors
I used my knowledge of vectors, and applied it to my final coolest physic concept. I saw the use of
vectors when sailing. When the (water) current is strong, it is hard to fight its strength to the finish line. The example we used in class we one with a river. To get to the other side, and taking into account the direction of the river, the fastest possible path across the river would be to go at an angle up stream. When these two vectors are then added, the result is a straight line to the other side of the river.

Wind Turbine

For our final physics assignment, we made a wind turbine. My group made the most successful wind turbine, courtesy of the 800 turns in our coils. To make our turbine work, we had to make a generator from coils of wire and four magnets. During this project, we created electricity with magnets; this is known as electromagnetic induction. To make our turbine work, we had to induce a current in the coil of wire by changing the magnetic field around the coil. We changed the movement of the charges by putting the magnet there, which realigned the charges which were going in all different direction, to make them all move in the same direction, helping to spin the turbine. This change from mechanical energy to electric energy is what makes the turbine a generator.

The materials we used to make our wind turbine were:
water bottle
coil wires

disk magnets
square dowel
round dowel
LED
fender washer

screws
wood for the platform
glue

We cut a water bottle in half, to fit in the template we cut out, and then glued it to the top and bottom. The water bottle was used to make the turbine spin and thus cause a voltage. Next, we punched a hole into the two cardboard pieces, and put the sharpened piece of round dowel through it, and then let it rest on the top of screw to keep it standing up, and also to let it rotate freely. The most important (and difficult because I'm so bad at wrapping coil apparently) was next. We made 4 coils that connected to each other. Each individual coil had 200 turns, to make a total of 800 turns. We then glued these four coils down onto the wooden base. We then used the fender washers and disk magnets to align with the coils to induce the voltage. All the poles of the magnets were facing the same way so that the current would go in the right direction. Finally, we attached the end pieces of the coils to a LED. Our wind turbine successfully produces a voltage. 

What made our wind turbine so successful was the amount of turns in our coils. The more turns, the more easily a current can run through it. The only problem we had was wrapping the coil 200 x 4 times, and then successfully getting the coils off the cardboard that helped us shape it. Over all, this project was a success for my group. On the final test, I struggled with a question involving wind turbines because I didn't really understand the concept fully. With this project, I was able to understand the function for all the components, and am now able to piece them all together to understand why a wind turbine works. 

Unit 7 Reflection

This unit, we began learning about magnetism first. The source of magnetism is moving charges. The charges (electrons) are spinning randomly when not magnetized. Domains, however, are clusters of electrons all spinning in the same direction. Magnetism gives them a net direction. This happens when a magnet is brought near a cluster of randomly spinning electrons. In order for the direction to stay the

same, and because the magnet is much stronger than the cluster of electrons, the electrons are all forced to align so that the magnetic field can continue to flow. In an electron flied, there are two poles. The North and south pole. The magnetic field runs out of north pole, and then to the south.

The reason the charges are forced to move this way in a magnetic field is because: like poles repel and opposite poles attract. When the electrons leave the north pole, they are attracted to the opposite pole (the north pole) that they were just repelling. 

There were three big questions asked this unit:

How do you turn a paper clip into a magnet?

The Domains in a paper clip are random, and a magnet had a magnetic field. When the magnet is close to the paperclip, the domains align to match the magnetic field of the magnet. The paperclip now has a North and South pole. The North pole of the paper clip is attracted to the South pole of the magnet, and thus the paperclip sticks to the magnet

Are cosmic rays harmful or helpful, considering the Earth's magnetic field?

The cosmic rays are helpful because there is a field around the earth, and when a charge enters the field, it circles around the file lines, all the way into the North and South poles. All moving charges feel a pull from a magnetic field if they are moving perpendicular to it. Because of this, when a moving charge out in space is moving perpendicular to the Earth's field lines, it gets sucked in, and because of the right hand rule, starts spinning around the field lines, right into the North and South poles. This is what causes the Northern Lights. We can only see them in the North and South poles because the charges are following the field lines into those poles, and that is where they are the most concentrated.  

How does a credit card machine read your card?

The credit card has a magnetic strip, which has a code. When swiped, the coils turn causing a current. The computer reads this current that is caused by the coils and counts the number of coils, letting the machine read your card. 

The right hand rule that I mentioned in the Norther Lights question, can be demonstrated in the picture:

The thumb represents the direction of the current of moving charges. The fingers curls around the thumb, representing the direction of the magnetic field. 

Electromagnetic Induction is the process of inducing voltage by changing the magnetic field of the loops of wire. The more loops in a wire, the greater the voltage is induced. Faraday's Law states that

the induced voltage in a coil is proportional to the product of its number of loops, the cross-sectional area of each loop, and the rate at which the magnetic field changes within these loops. There are three ways that voltage can be induced in a wire:

1. moving the loop of wire near a magnet

2. moving a magnet near the loop of wire

3. changing the current in a nearby loop

All of these methods involve changing the magnetic field in the loop of wire.

A transformer is a device used for increasing or decreasing voltage or transferring electric power from one coil of wire to another through electromagnetic induction. A transformer has 2 coils of wire. There is a primary, which is the input because it is directly connected to the power source. The other is the secondary. Electric current flowing through the primary coil causes a change in the coil's magnetic field. This spreads, inducing a voltage on the secondary coil. Voltage causes current, therefore, there is a electric current being transferred between the 2 coils. In order for the current to work, the transfer of electricity must be constant, and the only current that gives a constant surest is AC. AC current is constantly changing, while DC only goes one way, which wouldn't let the transformer work. 

Primary and secondary voltage relationship:

Primary Voltage    =   Secondary Voltage 

# of primary turns       # of secondary turns

energy is conserved, so power of primary = power of secondary. VI = VI. 

The last thing we learned about in this unit were motors and generators. Motors take electric energy (the input) and through electromagnetic induction produce mechanical energy (the output). Generators, on the other hand, take mechanical energy (the output) and with electromagnetic induction, make electrical energy (the input). Genorators produce a current as a result of motion. While the motor makes motion as a result of current.

Motors Make the World go Round

In this lab, we constructed a motor using a battery, a coil of wire, a paperclip, and a magnet. Each had their own function in making the motor function properly.
Battery: power source for the motor
Coil of wire: carries the charges and acts as a circuit connector
Paperclip: creates a domain that allows the current to continue the run through it
Magnet: provides a North and South pole for the current to flow through

To make the motor work, we had to strip both ends of the coil. We did this because the current was flowing out of the North pole of the magnet, going up towards the motor loop and through the coil ends into the paper clips, then back around to the South pole of the magnet. The motor turned because of the magnetic pull created by the magnet. This is because all the charges in the wire were moving the same way, but since the wire was coiled, the current would technically be in different directions. The vertical loop felt the force of the magnet in opposite directions on the top and the bottom sides so there was a torque on both ends of the wire, causing it to rotate. If the loop was horizontal, it would not feel this force in a perpendicular way and there would be no rotation. 

The motor is very small, in fact to small to power anything, therefore, we used this motor only for educational purposes. 

Here is a video of our motor working in action:

Unit 6 Reflection

Charges and Polarization including Coulomb's law:

Beginning our unit we started off learning about charges and polarization. Charges can be transferred from one object to another in three different ways: contact, friction, and induction. 

Contact: when someone is positively charged and they touch a negative person, causing a shock when the charges transfer.

Friction: Rubbing positively charged particles against negatively charged particles causing them to transfer.

Induction: 

 a) The metallic sphere is neutral (same number of protons and electrons) 

b) A negatively charged rod comes close to the sphere, causing the charges within the sphere to   separate (sphere is still neutral)

c) One side of the sphere is grounded, so the negative charges equalize with the ground, leaving that side of the sphere neutral, but the other side still positive (the sphere is now charged)

d) The connection to the ground is removed (sphere is still charged)

e) The rod is removed and the positive charges disperse throughout the sphere (sphere is still charged)

Being "polar" means that the charges have been separated. The object that has been polarized no longer has a charge, but instead is now neutral. 

Sooo….. How does a balloon stick to the wall without tape?

1. Balloon takes charges from hair (becomes negative)

2. balloon charges by friction

3. the wall polarizes when the negatively charged balloon comes near it

4. positive charges move closer to the balloon, negative charges move father away. (opposites attract)

5. the distance between opposite attractive charges is less then the distance between the like repulsive charges  

6. the attractive force is greater than repulsive force because of Coulomb's Law: F=kq1q2

7. larger attractive force = balloon sticks to wall                                                      d^2

Electric Fields: 
The area around  charge that can influence another charge is an electric field. 

The closer the lines are, the stronger the electric field. To the right is a picture of which direction the electric charge is going for both positive and negative electrons. 

The formula for the strength of an electric field is: E = f/q

Electric shielding is when an object inside the metal casing is protected so that whenever there is a charge that could effect the object inside the casing, the metal is used as a shield and protects from the charge, keeping the objects charge at zero always, and making sure the object feels no force. 

Electric Potential/Electric Potential difference, Capacitors:
Voltage is the same thing as potential potential. 
V = change in PE/q (units of Volts = V)

If two like charges were pushed together, they will repel and the electric potential energy will increase 

Birds, when standing on a wire don't get hurt because the bird is not experiencing potential difference between its feet, therefore no current flows. However, if the bird makes contact with the two different wires, it would be connecting a circuit with a potential difference (voltage) and current would flow through the bird. 

Flashes can't work continuous because once the flash flashes, the charges, much like capacitors, must recharge in order to flash again, depending on size, the charge recharges faster if smaller. 

Power, Resistance:

Current is the flow of charges (units: Amps (A) goes through the circuit)
Resistance (Ohms) simply resists the flow of charges. Making a wire thinner, or longer will increase the resistance. 

Ohm's Law --> V = IR
Power formulae --> Power = VI

Parallel and Series Circuits:

Series circuits are wires in such a way that all the electrical devices are connected along a single wire, such that the same electric current exists in all of them. 
Parallel circuits are wired so that the same voltage acts across each one, but a break in any one path does not interrupt the flow of charges in the other paths.

If a light bulb in the series circuit were to go out, then not the lights would go out because their current is connected. If a build in the parallel circuit were to go out, then, because their currents re not connects, the one build would go out, but the other on would stay on. With series, the more appliances added, the dimmer the light will be, but parallel's lights will stay the same.

Fuse breakers keep homes, which as wired in parallel, from burning. Because homes are wired parallel, the more appliances plugged in, the greater the current drawn. When a wire heats up because of the amount of current, it can blow. So a circuit breaker is there wired in series with the rest of the circuit to make sure everything goes off to keep it from blowing.  

What I found difficult and how I over came that: 
This unit I found potential difference very difficauly, and it took some ONKs and discussing it with my table, but when I was studying for a quiz one night and the answers to the ONK we had taken a few days before was online, I was reading the correct answers and finally got it when it was compared to a bird standing on wires. This was how I saw it and how it just clicked. 
A few times I had to stick with the problem, even thought it was difficult, and when in class, I would ask questions until I understood how to do it correctly and why I had done it wrong. 
My goals next unit are to not wait till half way into the unit to realize that I had been zoning out the entire time. Keeping up will save me in the long run.
In my room I saw an example of a series circuit  I have a power source where I plug everything in, and now I understand why it is so energy consuming: It takes more current to run all the appliances, and therefore, drains energy.

No Place Like Ohm

In this video, Hewitt explains how voltage is what flows in a current through a wire which can have a lot or a little resistance depending on its length and width. It also explains how to solve equations asking for the current (something that would have been helpful for my quiz..) when given voltage and resistance.

Voltage

In this video, voltage is explained in comparison to a lake, while current is explained in comparison to a river. Voltage is the potential deference and is explained by someone tilting a lake and the difference between the highest point and the lowest where the water starts flowing is the voltage. It explained everything with the assistance of current explanations that helped to tie it together. It helped to see it compared and then related back to electricity. 

Mousetrap Car Race

Kenna and I built a mousetrap car that traveled 5 meters in 2.84 seconds (our classes fastest!). In the picture below, you can see our mousetrap car. It is not very clear in the picture, but the body is made of hanger rods with a thin circular metal bar as the axis. We used the hanger rods because they were light weight and were easily bendable making working with them easier. We used the thin metal circular bar because it fit perfectly in the drilled holes on the hanger and also was small enough that we could wrap the string around it and attach it to the mousetrap and it wouldn't fail to unravel. To make the mousetrap roll, we

used CDs for wheels. We used these because they were the perfect size, being able to slice through the air with very little air resistance and also had very little rotational inertia, making the car move faster. We wrapped the CDs with a balloon because this caused the CDs to move with friction because the CD alone would not have any tract on the ground and would slid. We glued bottle caps to the sides of the CD because we wanted to metal rod to be able to rotate in the CD with little resistance, and the CD holes were to large so we

drilled holes in the bottle caps and put the rod through, letting it rotate easier. We didn't use a lever arm really because our model worked great without one, instead we attached the string to the rod and the mousetrap and when it set off, it worked great and produced enough force to send the mousetrap on its way for more than 5 meters and fast too!

Physics of the Mousetrap Car:

For this project, Newtons first law was seen when we used balloons to give friction to help the mousetrap car move faster and longer. The balloons were meant to add friction because there was not enough with just the CD's slippery sides. There was more inertia because there was friction to add traction so that the car moved farther without slowing down. We saw Newton's second law during this lab as well. Newton's second law says that acceleration is inversely proportional to mass, and is directly proportional to force. So, since we made the mousetrap car lightweight, we needed to have a large force so that the car would accelerate fast. Because we had a large force divided by a small mass, the acceleration was large, making our car move fast. Newton's third law was of course applied because what would physics be without all three of Newton's laws? For every action there is a reaction. When the mousetrap went off, the string started unraveling, and this caused the wheels to push the ground backwards, ultimately letting the ground push the car forward. 

To solve the problem of too much or too little friction, we wanted the perfect amount, so we used balloons to add friction because the CD alone would not work with its thin and slippery sides. This gave the wheels more traction to help stick to the ground. We also made sure to avoid anything dragging because that would only create more resistance. There was static friction with the wheels and the ground and there was kinetic friction when the mousetrap car was in motion and is stopping. 

We used three wheels because we didn't need more than that. We used two wheels in the back because we needed the axel to be attached to two wheels. This was necessary because we needed an axel to wind up the string, one wheel wouldn't have given us room to do this. In the front we didn't need an axel, so we only used one wheel. We decided to use CDs because they were thin and sliced though the air, and also, because they had a medium diameter, and because they were this size, they had very little rotational inertia. 

The law of conservation of energy tells us that energy can not be lost or created, only transferred. The mousetrap car did this because when we transferred our energy to the car by snapping the mousetrap, the potential energy was converted into kinetic energy that made the car go, the energy was not lost, but simply transferred to the form of something like heat, and to the ground with friction. 

For our car, we didn't use a lever arm, or you could say that we did but it was short because we only used the string attached to the trap. We decided to do this because we thought that that lever arm would only slow it down because it it took a long time to move and unravel the string, and thus slow down the wheels. Our lever arm was short and fast because as soon as the trap snapped, the axel was put into motion making the force so large that it continued to move the wheels week after the trap had gone. 

Rotational inertia is the number of rotations in a unit of time. We wanted all of our wheels to have the same rotational inertia because it made it easier. Then, another factor in deciding the kinds of wheels we wanted, was the tangential speed, how much distance is covered. We knew that because we had a small axel, the string unraveling would be quick and since the wheels were attached to the axel, we wanted larger wheels so that for every time the axel rotated once, the wheels would rotate, and this would make the car go fast. There was a lot of force from the trap snapping, so when the axel started to rotate, it continued to and the is caused the wheels to just as fast. Rotational inertia is when an object resists changes in the spin of an object. We chose to have out axel close to our wheels so that there would no be a lag time in which the trap shaped but we had to wait for the wheels to start turning because they were so far away. This proved to be helpful when the wheel immediately started rotating and moving rather quickly

We cannot calculate the amount of work on the spring because the spring is not parallel to the other parts of the car, and we cannot calculate the potential energy because we know that PE = mgh and we don't know the height, and would have to find the height. We can't calculate the kinetic energy because we don't know the velocity and once again would have to find the mass. Finally, we cannot calculate the acceleration of the spring because we don't know the distance the spring traveled or the speed it traveled. 

Reflection:

In our first design, we were going to use a wooden plank, but instead found that the hanger rods were more useful because they were light weight and we could attach an axel to them easier. We were also going to use a smaller wheel in the front, but decided that if all the wheels had the same rotational inertia it would be easier. 

One thing we really had trouble with when working on our mousetrap car was getting the axel straight so that the wheels both went straight and didn't curve. We had to red rill many times because the car would veer in one direction. Eventually we made the hole that the metal rod fit through smaller so that it wouldn't have room to move around. We also re-drilled and made the holes that the axel fit in straighter and this helped to get the car to move straighter. 

One thing that I wish I had done differently with this project was make everything perfect the first time so that I won't have to come back and redo it when it doesn't work in the end. If we had drilled the holes in line with each other in the first place, then we wouldn't have run into that problem in the end that forced us to come in outside of class. 

Unit 5 Reflection

This unit in physics I learned about…

Work and Power:
Work is simply a transfer of energy, the equation being:

Work = force x distance


In this example, the man is pushing a 20N box for 2m.
work = force x distance
work = 20 x 2
work = 40Nm

Because Nm is a strange unit, scientist decided to call the unit for work a Joule. Work and energy are measured in Joules. In another example where a man is lifting a box straight up 1m and the box weights  10N, then the work done will by 10 x 1 =10J.

A man is walking up stairs and weights 600N, The diagonal distance of the stairs is 10m, but the vertical distance is 4m. Something important to remember is that only the height matters, not the diagonal because…

--> FORCE AND DISTANCE MUST BE PARALLEL! <--

Therefore, the equation for this example will be:
work = force x distance
work = 600 x 4
work = 2400J
An example of a question where no work is done because the force and distance is not parallel is when a waiter is carrying a plate. The waiter is moving one way and the plate's force is going down. Because the force and distance is not parallel, no work is done. Another example of no work being done is when someone pushes on a wall and they are not going anywhere. Because there is no distance, there is no force (50N) being done:

work = force x distance
work = 50 x 0
work = 0J

power is simply how quickly work is done, and the equation is:

power = work
               time

Power, when solved comes out with an answer in Js. But the unit we use for power is a Watt.
1 horsepower = 746 watts
If I solve for the man's power in the first example where the work was 40J, and it took him 8 seconds to do this work, it would look like this:

Power = work
             time
power = 40
             8
power = 5 watts

Next in the unit, we learned about the relationship between work and kinetic energy. Energy is the ability to do work, and kinetic energy is the energy of movement. Therefore, Kinetic Energy is the ability to move. Work is the change is movement. Kinetic energy's equation is:

KE = 1/2 mv^2

If a 10kg car accelerated from 30-->40 in 5 seconds, and it took 100m to do this…
What would the change in kinetic energy be on the car?
KE = 1/2 mv^2               
KE = 1/2(10)(30)^2       KE = 1/2(10)(40)^2
KE = 4500J                    KE = 8000J
8000-4500 = 
change in kinetic energy = 3500J

How much work was done in the acceleration?
change in KE = work
therefore 3500J

What was the force that caused the acceleration?
work = force x distance 
3500 = 100f
100       100
F = 35N

What was the power of the car?
power = work
             time
power = 3500
               5
power = 700 Watts

In terms of work and energy what do airbags keep us safe?
KE = 1/2 mv^2
change in KE = KE initial - KE final
change in KE = work
work = force and distance

The change in KE will be the same no matter how the person is stopped
The work is the same no matter how you are stopped 
The airbag increases the distance over which the person is stopped, therefore results in a smaller force and thus less of an injury. 

In this example, the man is standing on a cliff and has KE = 0. We see PE and this means potential
energy. As the man falls down the potential energy becomes smaller and the kinetic becomes larger. The equation for potential energy is,

PE = mgh

When the potential energy goes up, the kinetic energy goes down and visa versa. If an object has height, that it has potential energy even if it is at rest, but if an object is at rest, than it doesn't have kinetic energy because KE requires velocity because of its equation.
When riding on a roller coaster that has many highs and lows, we know that the first hill must be the highest because in order for the coaster to make it over all the hills, it must have a larger enough potential energy at the beginning. This potential energy transfer to kinetic and this lets the coaster transfer energy when needed but never more than it had at the beginning.
Energy is never "lost". When we see that the energy does not line up the same as the beginning as it was in the end, this is simply because the energy was transferred into something like heat, light or sound.

The last thing we learned about this unit was machines. We first learned about the ramp. A ramp increases the distance over which the force is applied, thereby decreasing the amount of force required to do the same amount of work without a ramp.

*Work in = Work out
Work (ramp) = Work (lifting up)
Force x distance = Force x distance

We then learned about another machine: the bolt cutters. The bolt cutters have long handles and short blades. This is because:
The work on the handles equals the work done on the bolt by the blades. The long handles allow for a longer distance with makes a small force. The short blades to the same work, but instead have a short distance and a large force, allowing the bolt to be cut.

We then finally learned about pulleys. The concept of a pulley is the same as the machines mentioned above: The decrease the force, making it easier to do a task. This is an example of a pulley question:
You have a 4 string pulley and you are trying to pull a 1600N weight, how much weight are you actually pulling?

Work in = Work out
f x d (string) = f x d (pulley)
f x 4m = 1600N x 1m
f = 1600/4
force = 400N

What I found difficult and how I overcame it and saw connections in real life…

I found the change in kinetic energy difficult, but this was mostly due to the fact that I missed this class. I was able to understand this after looking at peers notes and then studying it well before the quiz. I think that I have done well with understanding this unit and feel very confident. When I did not understand something I ask for help around me, and when I got something wrong on a quiz I made sure to go back and write the correct answer in the margin so that I could go back and study correctly. My goals for the next unit are to continue making sure I understand what I am getting wrong on my quizzes. This really helped me and also aided me in feeling more confident. I want to also be able to write down a list of things I have problem with throughout the next unit and then go back at the end and see if I have grasped those concepts yet, and if not seek help and understand what I need to figure out to get it right.
I witnessed a situation with work when I was walking up to third Mitchell with a very heavy backpack and I thought to myself that I was working so hard, and that it would be a lot easier if I could just take an elevator or something so that I could work less. But then I realized that I would be doing the same amount of work, so I rephrased my wish and wished that I could take the elevator so that the force I was carrying would be less.

               

Inclined Planes

In this video, Bill Nye the Science Guy shows a simple machine example of the inclined plane. Nye shows that the distance vertically to the second floor is the same for both the pole, ladder and ramp, the only difference is the horizontal distance. The force is smaller, therefore making it easier, for the ramp because the distance is large.
Force x Distance = Force x Distance
The work in is equal to the work out, meaning that the work for both the pole and the ramp is the same. Both have the same amount of work, the difference is the small distance in the pole resulting in the large force, making it harder to climb up. The ramp has a large distance, so the force is smaller, making it easier to walk up. 

Do the Work, Produce the Power

In this video of a bunny running up the stairs, the bunny is doing work. When the bunny runs up the stairs, its force (its weight) and the distance vertically that it travels are multiplied and result in work. This bunny does not produce as much work as either a bunny running up a higher staircase or a larger bunny who weighs more resulting in a larger force. While the bunny is running, it is also producing power. The bunny's power is its work divided by the time it take for the bunny to run up the stairs in seconds. So the bunny is doing work and producing power in the video.

Unit 4 Reflection

This unit in physics I learned about…

Rotational and Tangential Velocity:
We began our unit by differentiating between tangential and rotational velocities.

Tangential Velocity: How much distance you cover
Rotational Velocity: Number of rotations per unit of time

We learned, for example, that when on a merry-go-round, the outside travels a greater distance vs. the inside. Therefore, since the outside has a greater distance to travel in the same time that the inside

travels, its tangential speed will be larger. Both outside and inside will have the same rotational speeds because they're rotating the same number of times, just at different speeds. We learned the same concept with a different example shown in the picture to the right. With the two gears, one has 24 prongs and the other, 12. This is a 2:1 ratio, and that means that the smaller gear, in two rotation, goes around twice as much as the larger gear which only went around once. This means that: The large gear has a smaller rotational speed vs the smalls gears large rotational speed. The tangential speeds for both gears are the same because any point along the edge of rather gear will cover the same distance in the same time interval.

Train wheels are made in a way that self corrects themselves. The larger part of the wheel is on the inside and the skinny part in on the outside. This is because when the train starts to go off track, the larger part of the wheel will be on the track at the same time that the small part is. The larger part of the wheel has a greater distance to cover in the same time as the small wheel, therefore it will move faster, and thus move itself back on track.

Rotational Inertia and Conservation of Angular Momentum:
The main thing to remember about rotational inertia is that there is a larger rotational inertia if the mass is farther away from the axis. This explains why ice skaters pull in their arms to spin faster.

Rotational Inertia: Property of an object to resist changes in the spin

Spinning velocity is all about the distribution mass. When an ice skaters arms are away from her axis of rotation, she will slow down, and she will have a large rotational inertia. But when an ice skater pulls her arms in toward her axis of rotation, she will move fast and have a smaller rotational inertia.

Angular momentum before = angular momentum after

This means that if you have your arms away from your axis of rotation, you will have a small rotational velocity and a large rotational inertia. Therefore, when you pull your arms towards you, your rotational inertia and rotational velocity will have to be opposite of the before (spinning with arms away) in order to have both momentums equal. So the equation will look something like this:

Rotational Velocity x Rotational Inertia = Rotational Velocity x Rotational Inertia

In the video form the movie Ice Princess, the ice skater demonstrates her rotational velocity increasing when she pulls her arms in vs when her arms are away from her. (Start at :35)

Torque and Center of Mass:

Torque = force x lever arm (distance form axis of rotation)

When you are trying to unscrew a screw with a wrench, what do you do to make it easier? There are two things that can help this, one is to add more force, and the other is to increase the lever arm, or do both. By doing these things, you will increase your torque and thus, make it easier to unscrew the screw.

The center of mass is the average position of an objects mass. So in the picture to the left, the three boxes have different centers of mass, and this either makes it easier of harder to push them over. For A and B the center of gravity is within the base of support, therefore the boxes will not fall over. But box 

C's center of mass is not within the base of support, therefore the box will fall over. In the example below that, the boxes all have the same center of gravity in the center of the box. The only difference is the angle of the box. In order for the box to stay up, the center of gravity must be within the base of support, and the only examples of this is in box A and B. Box C has a center of gravity that is out of the base of support and therefore will fall over. This is why in sport such as football, the players stand with their feet wide 

apart. This is done in order to create a wider base of support so that their center of gravity will be harder to move out of. They also bend their knees, and this is done so that their center of gravity is also closer to the ground so it is harder to knock them over. With a baseball bat balanced at its center of gravity. The side with the heavier end will weight more even though it is shorter. This is because the force on that side makes up for the short lever arm. Both sides have to have an equal torque, so therefore the baseball bat balances because one side has force and the other, a lever arm, thus creating no net torque. 

In the example below, a long stick is balanced. To find how many meters the ball is away form the fulcrum to make the system balanced, we use these steps and equations:


counter clockwise torque = clockwise torque

lever arm x force = lever arm x force  --> before and after

1x = 2(4)
x = 8m

These steps are the same to find the weight of the meter stick, just plugging in different numbers. 

Centripetal/Centrifigual Force:

Centripetal force: Center seeking force that keeps you going into a curve.

Centrifugal force: center fleeing force (fictional)

An example that we learned that helps to understand centripetal forces is: You are riding on a bus and suddenly wake up form your nap because the bus just turned. The force that causes you to slam into the person sitting next to you is the centripetal force. This is because the bus is moving towards the center, and you are still moving straight, so you hit the person next to you. Nothing causes me to hit the person, only the fact that I was moving one way and the bus was moving the other. 

An example to understand centrifugal force is: when the water flies out of a washing machine, there is no centripetal force, therefore the water moves in a straight line path and moves out of the washing machine.

The reason why a racetrack is elevated in because the cars need more centripetal force than friction or they would fly off the track into the stands. So in the picture, the fgravity is going straight down and the fsupport is going perpendicular to the car. When these vector are added together, the direction formed is in the direction of the center, thus the centripetal force. This force and the velocity going straight help the car to go in a curved path.

Difficulties this unit…

I found it hard to wrap my head around centripetal and centrifugal forces. But I was able to get past this by asking my piers and also going online and looking up videos about it and watching my piers blogs postings on it to gain there feedback and ideas about it. I was able to persist through the mass of a meter stick lab with my group by thinking about all the equations that we had learned thus far and putting it all together. This helped me to gain confidence, and this new found confidence has helped me to understand the unit better than other units before. My goals for the next unit are to improve my open note quiz grades by taking much better notes. The open note quizzes are very important because they help me to see where I am and what I need to know. But this will be easier if I already understand because of the helpful noted I take before.

Connections…

This unit, I was able to make a connection in the real world one day on the weekend when I was playing soccer with a friend. The friend I was playing with is very tall and I was able to knock him over because of physics. Because he did not have his feet spread apart to widen his base of support, and bend his knees to bring his center of gravity closer to the ground, I was able to knock him over. I found this the most interesting and personal even though I continued to find physics all over in the world around me.