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.
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 = 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.
