# Unit 4 Notes.

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Unit 4 Notes

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.

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.

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

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

Gravitational Energy Fg is 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

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

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

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

Power Power is the rate at which energy is used. P= ∆𝐸 ∆𝑡