Unit 5 Reflection

Work and Power

Work is the amount of force that is applied for a certain distance, and it is measured in Joules.
         WORK=FORCE X DISTANCE

If you were to lift up a box that weighs 20N 2m high, how much work would you do? Using the equation work=fXd you would get 400J.

You can only do work if you are lifting an object. You are not doing work if you were to just carry a box for a certain distance. You are not doing work, because the force and distance are parallel. The only way you can do work is if the force and distance are perpendicular (carrying a box).

Another example of someone doing work is running up a set of stairs.

The man in this picture has a force of 600N and he is moving up a set of stairs with a distance of 10m, how much work is he doing? 

      He would be doing 6000J of work. It is important to remember that the distance is not distance of

      the stair themselves but it is the height of the stairs. 

Power is the amount of work that is done in a certain amount of time, and it is measured in watts. Another way to word it is how quickly work is done. (power=work/time). 

Here's an example problem:
If you do 6000J of work in 60 seconds, how much power was produced?
    Power=work/time
    Power=6000/60
    600 watts

Work and Kinetic Energy

Work and energy are connected because work is the change in kinetic energy. This means that the work will always be equal to the kinetic energy. Energy is the ability to do work. Kinetic energy is the change of movement. It is related to the velocity because the equation is KE=1/2 mv^2. In order to fin the change of kinetic energy you must know the finial KE and subtract the initial KE.

Here's an example:

If a car is moving 20 m/s and requires 10m to stop. How many meters will it take to stop if the speed of the car is 40 m/s?

First you must realize that work=forceXdistance then remember work= the change in KE.
KE=1/2 mv^2
since you are going twice the speed you plug two in for v
which equals 4
this means you are going 4 times the speed and since work=KE you doing 4 times the work and going 4 times the distance.




Another question that is related to both work and KE is: why do airbags keep us safe?

Conservation of Energy

The conservation of energy means that the change in potential energy is equal to the change in kinetic energy. Potential energy is the energy stored within an object. It means that the energy has the potential to do work. In order to find the potential energy you must know the mass, gravity, and the height. The equation looks like this PE=mgh.
Kinetic energy is the energy of movement. It depends on the motion of an object. In order to find the kinetic energy you must know the mass and the velocity. The equation looks like this Ke=1/2mv^2.
The energy is conserved because when you lose one you gain the other.

Here is an example:

The ball doesn't hit the womens face because it was dropped from rest. This means it will not get any higher than it was dropped from. When she drops it the ball has the most amount of potential energy and the least amount of kinetic energy. The ball while in motion loses it's potential energy and when it is straight it has the highest amount of kinetic energy and the lowest amount of potential energy. 

Energy is always released in some shape or form. A car for example does not use all of its energy to accelerate forward. The energy is also released in ways like heat, light, vibration, and sound. 

In order to find out how efficient an object is you would calculate work out over work in.

Machines

Machines are used when you are trying to move a heavy object. They are useful because they make the objects easier to move. Machines make it easier because they require less force. They sacrifice force for more distance. If you were to lift the same exact heavy object without using a ramp you would do the exact same amount of work since work in = work out. The difference is that you use much more force when lifting the object over a short distance. With the machine you use more distance and less force.

Machines are not always used to lift objects. Another example are metal cutting shears. These shears have very long hands with much shorter blades.

These are able to cut through metal because the handles are long. This means that less force is required to use them. 

Here's an example question: If two people are in charge of putting some boxes into a bus that is 1m tall and they both grab 200N boxes but one person uses a ramp while the other lifts the boxes, who does more work?

They do the exact same amount of work because, one person uses more force while the other person uses more distance.
work= F X d
vs.
work= F X d

This unit in physics has been challenging for me. I felt rushed when learning these concepts and I never fully understood every aspect. I am comftorable  with work and power but once it gets into kinetic energy and potential energy I get lost. There are still 2 big questions that I am struggling with but I think with more time (when I study) I will be able to go over them a few times and be ready for the test. This unit though I would say I have caught up with.  I have done all of the homework assignments and watched all of the videos. I just feel like this is one of the hardest units and I still feel a little behind even though I have done all the work to stay caught up. I feel like I have put a lot of effort in though. Next unit I will continue to study for each quiz and begin studying for the tests further in advance. I think that now that I have prepared in advance for this test I should be ready!