Unit 3 - Energy and Momentum

3-1 Work and Force-Displacement Graphs
Work = force in direction of displacement x displacement

When a force is adding energy to an object, the work it does on the object is positive

When a force is removing energy from an object, the work it does on the object is negative

Kinetic and Potential Energy
All types of energy can be divided into two categories potential and kinetic

Energy is measured in J (joules)(kgm2s-2)

Kinetic Energy
Kinetic energy is energy that is 'moving' or 'used'

EK=mv2/2 (kinetic energy = mass x velocity squared / 2)

Potential Energy
Potential energy is energy that is being stored

Gravitational Potential Energy
EG=mgh (gravitational potential energy = mass x force of gravity x change in height)

9 Main Types of Energy
NOTE: Some of the following will fit in both categories

Potential Energy
Nuclear

Electrical

Gravitational

Chemical

Elastic

Kinetic Energy
Thermal

Light

Sound

Electrical

Law of Conservation of Energy
The law of conservation of energy dictates that energy cannot be created or destroyed only changed from one form to another. (This law is always true, until it's not (unit 7))

Elastic Energy
EE=kx2/2

3-3 Work and Energy Conservation
The law of conservation of energy states that energy cannot be created or destroyed and this is the formula that you would use for conservation of energy question

EK1+EG1+W=EK2+EG2+WF (intital kinetic energy + initial gravitational energy + work input = final kinetic energy +final gravitational energy +work done by friction)

Power
Power is the rate at which work is done (power = work/time)

Power is measured in watts (1 watt = 1 joule / 1 second)

Power is also equal to force times velocity

P=J/s

P=Fxd/s                     d/s = v (velocity)

P=FxV

Therefore P = J/s = FxV

Efficiency
Efficiency = Pout/Pinx 100% = Eout/Einx 100%

Momentum
Momentum is a measure of how hard it is to stop an object

p=m x v (momentum = mass x velocity)

The units for momentum are (kg x m/s) or (N/s)

Impulse
Impulse is the change in momentum

J = Δp (Impulse = change in momentum)

Newton's Second Law
FN=ma    a=Δv/Δt

FN=mΔv/Δt

FN= J/Δt = Δp/Δt

Force-Time Graph
The area under a force-time graph is the impulse

Law of Conservation of Momentum
The law of conservation of momentum states that momentum of a system remains constant regardless of any interactions in the system

Law of conservation of momentum has NO exceptions, it always works, and if it doesn't then you either did something wrong or you broke physics

Collisions
In all collisions momentum is conserved, however energy is another story

An elastic collision is when there is no energy lost

An inelastic collision is when there is a maximum amount of energy lost (ie the objects stick together)