3.3 work energy and power

work done

the energy transferred by a force

the force’s magnitude multiplied by its distance

W = F x D

symbol W, unit Joules(J) or Newton metres(Nm)

work done at an angle

if the force is at an angle to the body's direction of movement the component of the force parallel to the direction of movement is calculated using trigonometry and used

W = Fxcosθ

(F = diag force, x = distance, θ = angle)

energy

the capacity for doing work, has many forms

conservation of energy

energy can not be created or destroyed, only transferred between different forms

kinetic energy

the energy of a moving object with mass

E = 1/2mv^2

gravitational potential energy

the energy of an object due to its position in a gravitational field

E = mgh

elastic potential energy

the energy stored in an elastically deformed object

E = 1/2Fx or E = 1/2kx^2

electric potential energy

the energy of charges due to their position in an electric field

sound energy

the energy of a sound wave due to the movement of atoms

internal energy

aka thermal energy, the total kinetic and potential energy of the molecules moving within a body

electromagnetic energy

the energy stored within oscillating fields in electromagnetic waves

nuclear energy

the energy stored in nuclei which is released in nuclear reactions

chemical energy

the energy stored in chemical bonds which is released or absorbed during chemical reactions

power

the rate of work done

joules transferred per second, or the product of the force in newtons and the velocity in metres squared

P = Fv

symbol P, unit watts(W)

efficiency

the portion of input energy converted into useful output energy

efficiency(%) = useful output energy/total input energy x 100