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 EnergyW = F ∆xWork 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=