P1 Reducing Unwanted Energy Transfers (page 171) Flashcards
What are the ways you can reduce the amount of energy scampering off to a completely useless sotre?
Lubrication and Thermal insulation
(these are the ones you need to know about).
Lubrication reduces what?
frictional forces
Whenever something moves, there’s usually at least one frictional force acting against it (see page 210). Explain what causes this?
This causes some energy in the system to be dissipated (see page 170), e.g. air resistance can transfer energy from a falling object’s kinetic energy store to its thermal energy store.
(streamlining reduces air resistance too, see page 210).
How can friction be reduced between two objects rubbing together?
Lubricants can be used to reduce the friction between the objects surfaces when they more.
What are Lubricants?
they are usually liquids (like oil), so they can flow easily between objects and coat them.
How can heating occur?
by conduction and convection
When an object is heated, how is energy transferred?
it is transferred to the kinetic energy stores of its particles.
This causes the particles to vibrate more and to collide with each other. During these collisions, energy is transferred between the particles’ kinetic energy stores. This is conduction.
What is Thermal conductivity a measure of?
it is a measure of how quickly energy is transferred through a material in this way.
Materials with a high thermal conductivity transfer energy between their particles at a faster rate.
If particles are free to move (e.g. in a gas or a liquid), the particles move faster why?
the space between individual particles increases. This causes the density (see page 192) of the region being heated to decrease.
Liquids and gasses can flow, so the warmer and less dense region will rise above denser, cooler regions, so what happens with the particles?
the energetic particles move away from hotter to cooler regions - this is convection.
What do Insulation do?
it reduces the rate of enery transfer by heating.
What can you do to stop energy escaping outside the house after you’ve made your house nice and warm?
To prevent energy losses through heating:
Have thick walls that are made from a material with a low thermal conductivity. (the ticker the walls and the lower their thermal conductivity, the slower the rate of energy transfer will be (so the building will cool more slowly)
Use thermal insulation:
cavity walls
Loft insulation
Double-glazed windows
Draft excluders
Explain the thermal insulation for cavity walls?
Some houses have cavity walls, made up on an inner and outer wall with an air gap in the middle. The air gap reduces the amount of energy transferred by conduction through the walls.
Cavity wall insulation, where the cavity wall air gap is filled with a foam, can also reduce energy transfer by convection in the wall cavity.
Explain the thermal insulation for Loft insulation?
Loft insulation can be reduce convection currents (a cycle where air particles are constantly being heated, rising cooling and then sinking) being created in lofts.
Explain the thermal insulation for Double-glazed windows?
they work in the same way as cavity walls - they have an air gap between two sheets of glass to prevent energytransfer by conduction through the windows.
