ENERGY DISSIPATION

Question 1

what happens when a machine transfers energy for a purpose?

Answer 1

there’s friction between the moving parts of the machine, which warms up

-this means not all of the energy supplied to the machine is useful

Question 2

what is useful energy?

Answer 2

when energy is transferred to where it’s wanted in the way that it’s wanted

Question 3

what is wasted energy?

Answer 3

the energy that isn’t usefully transferred

Question 4

what happens to the energy transferred to any system?

Answer 4

some of the energy is transferred usefully and the rest is dissipated (spreads out) and may be stored in less useful ways

Question 5

how do the gears of a car get hot when it’s running?

Answer 5

it gets hot due to friction

-energy is transferred from the Ek store of the gear box to the thermal energy stores of the gear box and the surrounding air, increasing the temperature

Question 6

what eventually happens to useful energy supplied to turn the wheels of a car?

Answer 6

the Ek store of the wheels transfers to the thermal energy stores of the tyres by heating then transferred to the thermal energy store of the road and surrounding air

Question 7

what happens to energy the more it spreads out? + e.g.

Answer 7

it becomes less useful

• hot water from a central heating system in a building is pumped through pipes and radiators
• its thermal energy store decreases as it transfers energy be heating to the thermal energy stores of the radiators
• the heat will eventually be transferred to the surrounding air