A vacuum flask is a small masterpiece of physics. Silvered walls turn back radiation, a vacuum gap halts conduction and convection, and a stopper seals the top. Three transfer routes, all closed off, so your drink stays hot for hours.
Devices reduce or increase the transfer of thermal energy by acting on conduction, convection and radiation. Trapped air is a poor conductor that also cannot convect; shiny surfaces cut radiation; a vacuum blocks both conduction and convection.
Insulation works by reducing conduction, convection and radiation: trapping still air, using shiny surfaces, and sealing gaps where fluids could circulate.
It is the trapped air, not the fibres themselves, that does most of the insulating.
Switch the insulating features on and off and watch how each one cuts a different path for energy to escape.
Four quick checks. Each correct answer earns XP and lights this skill on your star map.
Materials such as wool and foam are good insulators because they...
A shiny silver surface on a flask reduces heat loss by...
The vacuum between the walls of a flask stops...
Loft insulation in a house mainly reduces heat loss by...
Good insulation tackles all three transfer mechanisms, each with its own trick.
In a fibrous insulator it is the trapped air, not the material itself, that does the insulating. Wool, foam and fibreglass work because they hold many small pockets of still air, which conducts poorly and cannot carry energy away by convection.
Unlocks once the four checks above are done. Worth more XP, written in the style of Paper 2.
A vacuum flask keeps a drink hot by reducing...
Why is trapped air such a good insulator?
Shiny foil is fitted behind a household radiator in order to...
That completes Unit 2, Thermal physics. Every skill in the unit is now lit.