1. Applications
1.1. lifting
1.1.1. work against gravity - W= mgh
1.2. elastic energy
1.2.1. stretching springs in mechanical systems
1.3. energy loss in friction
1.3.1. work done by friction converts mechanical energy to thermal energy
2. Problem solving strategies
2.1. work
2.1.1. draw diagrams involving displacement, forces and angles
2.1.2. W = Fd cos (theta)
2.2. energy
2.2.1. identify types of enegry (EPE)(KE)(GPE)
2.2.2. apply conservation of momentum - KE + PE = constant
2.2.3. use energy graphs for changes/time
2.3. power
2.3.1. use P = W/t or FV cos (theta)
2.3.2. solve for instantaneous power if velocity and force are shown
3. Connections to other topics
3.1. forces and momentum
3.1.1. work and impulse are related (change in momentum)
3.2. kinematics
3.2.1. use SUVAT to analyse displacement or velocity when calculating work or energy
3.3. thermal physics
3.3.1. energy losses due to friction or heat
3.4. circular motion
3.4.1. work done in centripetal forces = energy transformations
4. Work
4.1. definition
4.1.1. when a force causes displacement in the direction of the force
4.1.2. equation - W = F* d cos (theta)
4.1.3. units
4.1.3.1. W = work done (J)
4.1.3.2. F = force (N)
4.1.3.3. d = displacement (m)
4.1.3.4. theta = angle between force and displacement
4.2. key scenarios
4.2.1. positive work - work and displacement act in same direction, theta = o
4.2.2. negative work - work and displacement in opposite directions, theta = 180
4.2.3. 0 work - work is perpendicular to displacement, theta = 90
4.3. graphed
4.3.1. force-displacement graph
4.3.1.1. area under curve = work done
4.3.2. constant force creates straight line
4.3.3. variable force - irregular curve
5. Energy
5.1. energy types
5.1.1. kinetic energy
5.1.1.1. energy of motion
5.1.1.2. 1/2 mv^2
5.1.2. gravitational potential energy
5.1.2.1. energy due to height above reference point
5.1.2.2. gpe = mgh
5.1.2.3. 9 = 9.81ms^-2 near earths surface
5.1.3. elastic potential energy
5.1.3.1. energy stored in stretched or compressed springs
5.1.3.2. hooke's law - F = kx
5.1.3.3. epe = 1/2 kx^2 where k = spring constant and x= extension
5.1.4. other: nuclear, thermal, chemical, light, sound
5.2. work energy theorum
5.2.1. work done in a system = its kinetic energy
5.2.2. W = ke = 1/2mvf^2- 1/2mvi^2
5.3. conservation of energy
5.3.1. energy cannot be created or destroyed
5.3.2. KEinitial + PEinitial = KEfinal + PEfinal
5.3.3. mechanical energy = sum of KE and PE
5.3.3.1. without external forces (e.g. friction) ME = conserved
6. Power
6.1. definition
6.1.1. power is the rate at which energy is transferred
6.1.1.1. P=w/t = change in E/t
6.1.1.2. P = power (W)(J/s)
6.1.1.3. W = work (J)
6.1.1.4. t = time (S)
6.2. instantaneous power
6.2.1. a force causing velocity
6.2.1.1. P = F*V cos (theta)
6.3. graphed
6.3.1. work-time graph
6.3.1.1. gradient = power
6.3.2. power-time graph
6.3.2.1. area under graph = work done
7. Efficiency
7.1. definition
7.1.1. the ratio of useful power output to total power input.
7.1.2. efficiency = (useful energy output/total energy input)x100
7.2. power efficiency
7.2.1. using power, efficiency = (useful power output/total power input) x100
8. Graphical representations
8.1. force-displacement graph
8.1.1. area under graph = work done
8.2. energy-time graph
8.2.1. tracks energy changes over time
8.3. power-time graph
8.3.1. area = work done