In the latest Chapter of Physics, we studied Work, Power, and Energy.
Work is the measure of force that is applied to an object over a distance that is parallel to the said force. The most important word in the preceding sentence is PARALLEL. If the force is not parallel to the distance it is being moved, no work is generated. For example, the act of a person walking up a flight of stairs generates force, while the act of carrying a book across a classroom does not. In the case of the book being carried across a classroom, the force of the book is downward, while the distance is from left to right, meaning that the two are perpendicular, and no work is generated. The equation for work is:
W = F x D
Where F = Force and D = Distance. For example, if a 100 N man runs up a 7 m high staircase, he exerts 700 Joules of work. In terms of work, it does not matter whether the man runs or walks. His speed does affect his Power, however.
Power is essentially a rate of work. The equation for Power is P = Work Done/Time Interval. Therefore, if you are to exert 500 Joules in 5 seconds, your power is 100 watts. In the following video, let's pretend Rocky weighs 100 N, and the stairs are 30 meters high. He would exert 3000 Joules of Energy.
He also runs up the stairs in 8 seconds. Therefore, we would use the equation P=W/t and substitute, leaving us with P= 3000/8 and find that he exerted 375 watts of power. That's why he is a beast!
The next item we learned about is Gravitational Potential Energy. The equation for potential energy is PE=mgh, or if you know the force, it is PE=Fh. The h is significant because it stands for height. Height is the most important aspect of potential energy. This is because the high the object is, the more potential energy it has, and ultimately the more kinetic energy it can have.
Kinetic energy is the energy found in moving things. The faster something is moving, the more kinetic energy it has. Kinetic energy is proportional to work because of the equation Change in Work = Kinetic Energy. The true equation for KE is KE=1/2mv^2.
As an object loses potential energy, it gains kinetic energy. This is due to the Law of Conservation of Energy. This law is what inhibits the operation of roller coasters. Have you ever noticed that the first hill is always the tallest? This is because that first hill gives the coaster alot of potential energy, which means it will be converted to alot of kinetic energy, giving the car enough speed to get through the rest of the track. Watch closely on this roller coaster:
It is easy to see that the first incline is the tallest, and gives this ride alot of speed for the rest of the track.You can literally feel the physics!
The next topic we discussed was machines. Machines are designed to help us exert less force and get more force out. The most simple machine is a pulley. Pulleys are designed to decrease the force while increasing the distance to increase the force outcome. Watch how Jack and Jill use a pulley to pull water out of a well in the following video:
You can know just how well a machine is doing its job by finding the efficiency of it. To find the efficiency, you simply use the equation, Efficiency = work done/work expected and convert the answer to a percentage. It is impossible to have a machine with 100% efficiency because energy is always lost as heat or friction.
Reflection:
Overall, this unit was not too challenging. My problem solving skills did not suffer to much because most of the equation are easy to remember and use. I found the need often to be very specific in my answers, because there are many trick questions in this chapter.
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