Unit 4 Notes

1. Unit 4 Notes

2. LOL Charts There will be an L at each time you want to show how the energy in the system is distributed. Between each L, the O shows energy entering or leaving the system. Energy commonly leaves a system in the form of heat and sound.

3. Common Types of Energy • Eg is gravitational potential energy. It is proportional an object’s height above the earth’s surface. • Ek is kinetic energy. It is the energy of motion. • Eel is elastic energy. It is the energy stored in a spring or other stretchy object. • Eth is thermal energy. It is proportional to temperature. • Ech is chemical energy. This is stored in chemical bonds. We rarely use this in physics.

4. Pie Charts • The size of the slices shows how the energy is distributed. • When energy leaves the system, we show the amount that left as Es

5. Work and Energy W = F ∆x Work is force multiplied by change in position. Unit: Joules (J) = Newtons x meters (Nm) When a system does work, it gives energy to something else. When work is done on a system, it receives energy. The amount of work done is also the area underneath an F vs ∆x graph

6. Gravitational Energy • Fgis basically constant. • If I lift up an object to a height h, I do work on it and give it energy • W = Eg= Fg ∆x • Eg= mgh

7. Spring Energy • In our lab, we found that a spring force is proportional the change in its length from equilibrium (Hooke’s Law) • The area under its F vx ∆x graph is the area of a triangle. Specifically, Eel=1/2 k (∆x)2

8. Kinetic Energy Ek=1/2 m (v)2 As you can see, Ek is directly proportional to mass and to velocity squared.

9. Conservation of Energy • Energy is never created or destroyed, but it does change forms • The initial energy of a system plus any energy added to the system is equal to the final energy of the system plus the energy that leaves the system. • E0 + Einput = Ef+ Edissipated

10. Power • Power is the rate at which energy is used. • P=