Physics p1.2 - conservation and dissipation of energy

conservation and dissipation of energy

What is the key point for energy transfer ?

Energy can be transferred usefully, stored or dissipated but can never be created or destroyed.

What term is used to describe dissipated energy and what is it?

Wasted energy - unwanted energy transfers.

What eventually happens to the energy in in these transfers?

It is eventually all transferred to the thermal energy store.

What are the two ways that energy is transferred through heating ?

• Conduction

• Convection

What is conduction ?

What form does it occur in ?

where vibrating particles transfer energy to near particles.

Conduction takes place in solids.

What is convection ?

What form does it occur in ?

when energetic particles move freely, from hotter to cooler regions.

They take place in liquids and gases.

Explain the process of conduction when it’s heated?

The particles vibrate and collide, which causes energy to be transferred between the particles’ kinetic energy store.

This continues until energy is transferred to the other side of the object, which is then transferred to the thermal energy store of the objects surrounding.

How can wasted energy be reduced?

• Lubrication - energy lost due to the reduced friction.

• Thermal insulator - reduced heat loss

• Streamlining - changing the shape of an object, so that it doesn’t affect air resistance as much.

How does ‘lubrication’ reduce wanted energy transfers ?

When objects are rubbed together, lubricants are used to reduce the friction between the objects surface when they move .

For example, liquids like oil are used to coat objects so that they can flow easily.

1. How does thermal conductivity of a material affect the rate of energy transfer?

2. How does levels of thermal conductivity effect the rate of heat loss?

• Higher thermal conductivity of a material = higher rate of energy transfer by conduction across the material

• Lower thermal conductivity = Lower rate of heat loss

• higher thermal conductivity = higher rate of heat loss

Describe how the rate of cooling of a building is affected by the thickness and thermal conductivity of its walls?

• Thick walls made of a material with low thermal conductivity. - the slower the rate of energy transfer so the building will cool more slowly.

• For example, captivity walls - has a inner and outer wall with an air gap that’s filled with foam in the middle. - reduces energy transfer by convection.