P1- 1.7

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P1- 1.7- ENERGY TRANSFER BY DESIGN

Lots of things can go wrong if we do not control the energy transfer. For example in a car engine

The vacuum flask:

- The vacuum between the two walls of the container cuts out energy transfer by conduction and convection between the walls

- Glass is a poor conductor so there is little energy transfer by conduction through the glass

- The glass surfaces are silvery to reduce radiation from the outer wall

- The spring supporting the double-walled container is made of plastic which is a good insulator

- The plastic cap stops cooling by evaporation as it stops vapour lose from the flask. In addition, energy transfer by conduction is cut down because the cap is made from plastic

The liquid slowly transfers energy to its surroundings so its cools down. This takes place at a slow rate.

Factors effecting the rate of energy transfer:

- The material the objects in contact with

- The objects shape

- The objects surface area

- Objects mass and material- They affect how quickly its temperature changes