Unit 5 Reflection

      The first thing we learned about in this unit was work and power. The formula for work is force times distance and the formula for power is work/time. I found out that work and power are related because you must have work in order to find out the power. One of the most important things we learned about was that in order for there to be work, the force and distance must be parallel. If they are perpendicular, then there is no work done. We also needed to remember that when working with stair problems, we should use the vertical height as the distance. The units for work are joules and the units for power are watts (aka joule/second). We also talked about horsepower, and we learned that 1 horsepower is equal to 746 watts. So if we did 1600J of work in 2 seconds, then we would have made enough energy to make one horsepower. As you can see in this image, the vertical height it was is important when calculating the work.
      The next thing we learned about was kinetic and potential energy, as well as the relationship between work and both KE and PE. We found that work is equal to the change in KE, or movement. The formula for KE is 1/2mv^2. When solving problems that ask how much greater the distance will be when a car stops at two different speeds, it is important to remember that the velocity is squared. So if the car stopped at 5m/s, then at 10m/s, you could say that the velocity doubled so you would put in a 2 for the v. That would mean that the distance, work, and KE are all 4x as much, since 2^2 is 4. We also learned that PE is PE=mgh. When asked if something can be moving and have PE, I found that this is true. It's PE could be decreasing as it moves but it could still have some as it converts into KE. Also, ∆KE=∆PE.
In this animation, the ball has all PE at the top and no KE. In the middle, it has equal or almost equal KE and PE. When it hits the bottom, it has all KE and no PE.
      The conservation of energy states that energy can neither be created nor destroyed. When connecting this to what we just learned about KE and PE, we could say that the energy must be conserved at all times. One example we used was that if we threw a ball in the air with air resistance, would it return to it's starting position with the same, less, or more KE than it started with? Well, KE is basically speed, and air resistance slows things down, then the answer would be less KE. Another example we used and actually demonstrated in class was a pendulum, where the ball would start out with some PE and would return to it's starting position with slightly less PE each time. It would never return with more PE or KE or else it would violate the conservation of energy.
      The last thing we learned about is simple machines. A machine is used to reduce the force in which it takes to push or pull something. The first machine we learned about was an inclined plane. A few key equations we had to remember when working with machines was that work-in=work-out and f-in x d-in= f-out x d-out. YOU CAN NEVER PUT IN LESS WORK IN A MACHINE THAN YOU GET OUT. If you got more work out than you put in, the machine would violate the idea that machines can't be more than 100% efficient. To find the efficiency of a machine, you take the workout/work-in and then multiply it by 100 to get a percent. The main reason that machines work is because they increase the distance so that the force is less. An example would be if you were trying to load a 30N box into a 1 meter high truck by using a 3 meter long ramp. Both lifting the box straight up and using the ramp use the same amount of work, however the ramp increases the distance so that the force is less as you push it up. Another example we used was that when cars drive, they don't use all of the joules of work. The remaining joules get converted into heat, sound, etc. So when your engine is both loud and hot, you are wasting a lot of the work your car could be using to move your car.
      I found this unit somewhat challenging; the hardest thing for me was remembering all of the equations and how they relate to each other. Other than that, I feel that I did fairly well on the quizzes, and my groups podcast was both funny, informative, and clever. We all tried to make a rap that incorporated as many details as we could but still sound good at the same time. I also kept up with all of my homework which was very helpful because I never felt left behind. Overall, this was a fun unit to learn about and I enjoyed how it was taught and related to the real world.