Unit 5 Blog

In this unit we talked about work, power, kinetic energy, the Law of Conservation of Energy, potential energy, and machines. I found it most difficult to understand how potential energy and kinetic energy were relative to each other and I think that I could have been more attentive in answering homework questions from the text book. However, I think I did very well in preparing for quizzes.
Work
Work is the force times the distance traveled (work=fd) and is measured in joules(J). In order for work to be done the force and the distance must be parallel to each other, for example when someone picks up a book from the ground work is done on the book. When the person starts to walk with the book there is no work done on the book because the person is walking horizontally and the force of the book is vertical. So if you walk up a staircase that is 6 feet tall (since the distance of the staircase is vertical it is parallel to the force of the book) holding a 20 newton book you would do 120 joules of work. Work=20N x 6ft, so Work=120J.
Power
Power is how quickly work is done (power=work/time) and is measured in watts. Lets say that when you walked up the staircase in the work example it took you three seconds, this means that you would have 40 watts of power. Work=120J and time=3 so, Power=120/3 or Power=40 watts.
Kinetic Energy
Kinetic Energy (KE) is the energy of movement and the ability to do work and is measured in joules. In order to find the KE you multiply 1/2 by the mass and velocity squared (KE=1/2 mv^2). In order to find the change in KE you would subtract the initial KE from the final KE. the change in KE is also equal to work, fd=1/2 mv^2. This also means that if the velocity doubles or triples then the work will either quadruple or be nine times the original amount of work.
Law of Conservation of Energy
 The law of conservation of energy states that energy can not be created or destroyed, it can be transformed from one form into another and is conserved, the total amount of energy never changes.
Potential Energy
Potential energy(PE) is the energy that is stored and held in readiness or the mass times the gravitation pull, or 10, times the height (PE=mgh). An example of potential energy is a rock tittering at the top of a mountain, if the rock weighed 20kg and was 50 ft high then the PE would be 10000 Joules (PE=20x10x50). The PE of this rock is also an example of Gravitation Potential Energy which is PE due to elevated positions. PE only has significance when something changes. The PE at the top of the mountain would be equal to the KE of the rock right before it hits the ground, this is because the PE is transferred into KE due to the law of conservation of energy.
Machines
Machines are meant to make the force you apply in less and the the force applied to an object larger, but the amount of work done will always be the same (work in= work out or f x D= F x d). Machines don't have to be in complicated, for example an inclined plane is a machine. It increases the distance traveled so that the force that you apply to get the object up the inclined plane decreases. This podcast I made in class explains machines.