Mechanics - Work, Energy and Power

Work

defined as the product of force and displacement

W = F x s

Work = Force x Displacement

Unit of work

Joule (J)

Energy

the ability to do work

OR

the amount of energy something has is also the amount of work it can do

Work Energy Principle

The change in the energy of an object is equal to the work done on the object

Kinetic Energy

energy an object has due to its motion

Kinetic energy formula

Ek = 1/2 mv ^2

Potential energy

energy an object has due to its position in a force field

Potential energy formula

Ep = mgh

Strain potential energy

when a force is applied to an elastic body so it changes shape. Work done by force becomes stored as strain potential energy

Gravitational potential energy

the energy a body has because it can fall to a lower level due to its weight.

The higher it is above ground, the more work it can do and greater potential energy it has

Principle of Conservation of Energy

Energy cannot be created or destroyed but can only be converted from one form to another

loss in potential energy = gain in kinetic energy

gh = 1/2 v^2

Collisions

when two objects collide momentum is conserved provided no external forces act on the system

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Is kinetic energy conserved?

No - some of it can be converted to sound and heat energy

Power

The rate at which work is done

Or

The rate at which energy is converted

Power formula

P = work done/ time

OR

energy converted / Time

Percentage efficiency formula

Power out / power in x 100/1