changes in energy and energy transfer

what is work

when a force causes an object to move in the direction of the force

what is the formula for work

work (J) = force (N) x distance (m)

what happens when work is done

the energy store of the object is changed

how is electrical work done by a battery

when the battery makes a current flow

what is power

the rate at which energy is being transferred

what is the formula for power?

power (W) = energy transferred (J) / time (seconds)

what are the ways energy is transferred

• mechanically (work is done by a force)

• electrically (work is done by moving charge)

• heating

how do you calculate energy?

1. kinetic energy = ½ x mass x (speed)²

2. elastic potential energy = ½ x spring constant x (extension)²

what does it mean to dissipate

to scatter in all directions, or to use wastefully.

what does it mean when energy is dissipated

we cannot get it back, as it has been spread out and heated up the surroundings

how is energy dissipation reduced?

• power station - designed to reduce the amount of waste energy

• car design - engineers design fuel efficient cars, that dissipate less energy. the car is also made streamlined to reduce air resistance and moving parts of the car are lubricated with oil to reduce friction

• chimneys - by having a chimney in the house energy can be transferred into rooms upstairs

• walls - walls have foam in between them, which makes them good insulators. thicker walls slow down the rate of energy loss

• loft insulation and carpets - reduce energy loss through the roof and the floor

• double glazing - reduces energy loss through the windows. a layer of gas trapped between two panes of glass provides good insulation

what is efficiency?

the proportion of energy that is usefully transferred in a process

what is the formula for efficiency

efficiency = useful output energy transfer / total input energy transfer

how is friction prevented

• using wheels

• lubrication

how is air resistance prevented

• travelling slowly

• streamlining

what is conduction

the process where vibrating particles transfer energy onto the neighbouring particles

what is convection

where energetic particles move away from hotter to cooler areas