Engergy Flashcards
Work
Application of a force and a resulting movement of that force.
Work = force x distance
Unit of measurement of work
Work = force (N) x distance (m) Work = N x m Work = Joules
2 categories of work
- Work is done against another force
- Work done to change the speed of an object
- both involve transfer of energy
Power
Amount of work done per the time
Power = work done / time interval
Unit of measurement for power
Work (J) / time (s) = Watt
(One horsepower = 3/4 kilowatt
Mechanical energy
Something that enables an object to do work
- measured in joules
1. Energy due to position of something (potential)
2. Movement of something (kinetic)
Potential energy
Energy stored and held in readiness
Gravitational potential energy
Potential energy doe to elevated position
PE = weight x height
Kinetic energy
Energy of motion
- depends on the mass of the object as well as speed
- kinetic energy of a moving object is equal to the work required to bring it from rest to that speed, or the work the object can do while being brought to rest
KE = 1/2 mass x speed^2 KE = net force x distance
Work-energy theorem
Work = change in KE
- if a car is going 2x as fast as another, it takes 4x as much work to stop as KE depends on speed^2
Work is NOT
… a form of energy, but a way of transferring energy from one place (form) to another
Other types of energy
- KE: temperature, sound intensity
- PE: electric changes (voltage), sound intensity
Law of conservation of energy
Energy cannot be created or destroyed; it may be transformed from one form into another, but the total amount of energy never changes
Machines
Device for multiplying forces or changing the direction of forces. Work on the principle of conservation of energy
Lever
Simple machine
- (Fd) input = (Fd) output. — friction ignored
Fulcrum
Point of support on which the lever rotates
- when close to a load, a small input force will produce a large output force. Input force is exerted through a large distance and the load is moved through a correspondingly short distance
1st class lever
Lv___________F^
*
2nd class lever
_____Lv_____F^
*
3rd class lever
_____F^_____Lv
*
Efficiency
Machines are not 100% efficient. Some energy is dissipated to molecular kinetic energy (thermal energy)
Efficiency = useful energy output / total energy output
