conservation and dissipation of energy

chemical energy store

Energy due to the bonds between particles, stored in food, batteries and fuels

kinetic energy store

energy an object has if its moving

elastic potential energy

the energy of stretched or compressed objects

thermal energy

energy an object has because of heat

Where can energy be transferred?

from one store to another

give me three ways energy can be transferred?

• heat

• waves

• when force is moved in a object

conservation of energy

Energy cannot be created or destroyed

closed system

an object which no energy transfer takes place out or in the energy store

example of closed system

when a person stretches an elastic band the energy store of the muscle decreases but the elastic potential energy increases

In terms of energy stores, what happens when you swing a pendulum?

• when its towards the middle gravitational potential energy decreases and kinetic energy increases

• when its away from the middle kinetic energy decreases and gravitational potential energy increases

what happens when force is applied to move an object?

energy is transferred to the object work is done on it

what is energy and work measured in

Joules (J)

equation of work done

Work done (joules) = Force (N) x Distance (m)

friction

A force that opposes motion between two surfaces that are in contact

what energy store those friction transfer

kinetic energy store from an object to thermal energy store

gravitational potential energy

Potential energy that depends on the height of an object

what happens when an object is moved upwards?

gravitational potential energy increases and this increases the work done by the gravitation force acting up

what happens when an object is downwards?

gravitational potential energy decreases and the decrease is equal to the work done by the gravitational force acting on it

what is gravitational potential energy equation

mass (kg) x gravitational field strength (N/Kg? x height (m)

what is the gravitational field strength in earth

9.8 N/kg

kinetic energy equation

1/2 x m (Kg) x v squared (m/s)

how is an object being described as elastic?

if it regains its original shape after being stretched or squash

elastic potential energy equation

1/2 x k (N/m) x e (m)

useful energy

Energy transferred to where it is wanted in the form it is wanted.

wasted energy

Energy that is not usefully transferred

what happens when energy dissipates?

It gets less and less useful

How is friction helpful?

Friction is helpful when cars want to stop the breaks are helpful because they do not skid off the road.

what happens if you brake a car in terms of energy stores?

kinetic energy of the car decreases and the thermal energy store of the brakes increases

input energy

energy supplied to a device

energy that is usefully transferred in a machine?

useful output energy

equation for conservation of energy?

input energy= useful energy transferred by the device/total energy supplied to the device x 100

how much efficiency does a device have?

0 and 1 or (100%)

different ways machine waste energy?

friction, air resistance, electrical resistance

how can you make machine more efficient?

Use a lubricant, which reduces friction between moving parts of a machine, reducing thermal energy transfer, reducing energy that is wasted.

how is energy in home supplied?

electricity, gas and oil

how is light bulb useful energy?

light waves emitted from filament

how is speaker useful energy?

sound waves from vibrations of speaker cone

how is television useful energy?

light waves and sound waves

how should appliances be designed?

waste as little energy as possible

power

the rate at which work is done

what is the unit of power

Watt (W)

what is the unit of watts equal to

1 joule in one second

what is the equation for power

power (w) = work(J)/time(s)

equation for power wasted

Total power in - useful power out

Equation for efficiency

Useful energy output / total energy input x 100