Topic 8- Forces doing work

all objects have energy in their ___ energy store?

all objects have energy in their ___ energy store?

thermal

electrostatic energy store

energy stored when repelling charges have been moved closer together or when attracting charges have been pulled further apart

when is energy transferred mechanically?

when a force acts on an object over a distance

when something changes in a system, ___ is transferred

energy

open system

allows the exchange of energy and matter to our from its surroundings

closed system

can exchange energy but not matter to or from its surroundings

isolated system

does not allow the transfer of matter or energy to or from its surroundings

change in energy in a closed system during energy transfers

in closed system energy transfers, there is no net change to the total energy

work can be done by: (2 things)

• forces acting on an object

• a current flowing through an electrical circuit

heating can be done by: (2 things)

• heating particles

• radiation

work is done when…

an object is moved over a distance by a force (in the direction of movement)

if a force is applied to an object, but doesn’t result in movement, is work done?

no

work done is the same as

energy transferred

work done formula

work = force x distance moved

gravitational store

the energy an object has due to its height in a gravitational field

change in gravitational potential energy formula

ΔGPE = m x g x Δh

kinetic energy store

the amount of energy an object has as a result of its mass and speed

kinetic energy formula

KE = ½ x m x v²

perfect energy transfer

no wasted energy

work done against air resistance, frictional forces and electrical resistance all result in…

heating (wasted energy)

power is the rate at which…

energy is transferred (therefore also work done per unit time)

power formula

P = E/t

power is measured in…

watts (W)

1 watt is the same as

1 Joule per second

efficiency equation in terms of power

efficiency = useful power output/total power input x 100

rearrange the efficiency equation to find total power input

total power input = useful power output x100 / efficiency