# Work, Energy & Momentum

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1. Energy
Property of a system to do work.
2. Kinetic Energy
Definition, formula, SI units
is energy of motion.  Objects that have mass and are moving with some velocity will have K.

K=(1/2)*m*(v^2)

Joule (J) = kg*m2/s2
3. Potential Energy. Definition, formula, SI units
Object is said to have a potential energy when it has a potential to do something.

• U=mgh
• J= kg*m2/s2
4. Total Mechanical Energy
is a sum of object's potential and kinetic energies.

E=U+K
5. The first law of thermodynamics
energy is never created or destroyed.
6. Conservation of Mechanical Energy
E of the system is conserved in absence of friction.  The sum of a system's potential energy and kinetic energy will be constant.
7. Work -- definition, formula, SI units
Work is not a form of energy, but a process by which energy is transferred from one system to another.

W=F*d*cosθ

J=N*m=kg*m2/s2

• θ is an angle btw force and displacement vectors
8. how many ways are there to transfer energy from one system to another.
Work and Heat
9. Power -- definition, formula, SI units
the rate at which energy is transferred from one system to another.

P=W/t

Watt (W) = J/s
10. Work-Energy Theorem
W-E Theorem offers a direct relationship btw work done on an object by all forces and the change in its kinetic energy:

Wnet=ΔK=KEf - KEi
11. Momentum
Formula and SI Units
• Quality of objects in motion.
• p=mv
• kg*m/s
12. All objects that have momentum, also have...
Inertia -- the tendency of the objects to resist changes in their motion and momentum.
13. Impulse: Definition, Formula, SI Units
• Impulse is a change in momentum
• I=FΔt=Δp=mvf - mvi
• kg*m/s
14. Elastic Collisions
Define
Give an Example
p conserved?
KE conserved?
• Where objects don't stick together.
• E.g. Billiard balls
• p conserved:  p1i + p2i = p1f + p2f
• KE conserved: KE1i+KE2i = KE1f+KE2f
15. Inelastic Collisions
Define
Give an Example
p conserved?
KE conserved?
• Where objects don't stick together
• E.g. two cars crashing
• p conserved:  p1i + p2i = p1f + p2f
• KE not conserved: ΔKEi > ΔKEf
16. Completely Inelastic Collisions
Define
Give an Example
p conserved?
KE conserved?
• Where objects stick together
• E.g. 2 cars crashing and becoming one.
• or two molecules colliding and becoming one (covalent bond).
• p conserved:  p1i + p2i = (m1+m2)*vf
• KE not conserved: ΔKEi > ΔKEf
17. In what type of collisions is momentum conserved?
In all collisions