Transcript Unit 4 Notes - Chandler Unified District

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