Power and Reducing unwanted energy transfers

Question 1

what is Power?

Answer 1

the rate of energy transfer or doing work

Question 2

what is power measured?

Answer 2

Watts

Question 3

how can you calculate power?

Answer 3

P = E ÷ t
- Power (W)
- Energy Transferred (J)
- time (s)
P = W ÷ t
- Power (W)
- Work Done (J)
- time (s)

Question 4

what is Lubrication?

Answer 4

it reduces frictional forces

Question 5

what is friction?

Answer 5

it acts between all objects that rub together, this causes some energy in the system to be dissipated

Question 6

how is Lubrication used?

Answer 6

it reduces the friction between objects

Question 7

how do things get warm/warmer?

Answer 7

• when part of a material is heated, that part of the material gains energy
• this energy is transferred across the material so that the rest of the material gets warmer

Question 8

what is Thermal Conductivity?

Answer 8

a measure of how quickly energy is transferred by conduction through a material

Question 9

what are materials with low and high thermal conductivity?

Answer 9

HTC - transfers lots of energy in a short time

LTC - thermal insulators, which reduces unwanted transfers by heating

Question 10

what does how quickly a building cools depend?

Answer 10

• the thicker the walls, the slower it will cool
• thermal conductivity of its walls, building walls with a low thermal conductivity reduces rate of cooling
• how much thermal insulation there is (e.g loft insulation reduces energy losses through the roof)