Physics revision

Energy

Conservation of energy- Energy cannot be created or destroyed , it is just transformed into other forms.

Kinetic- Anything that moves.

Gravitational potential-Any mass in a gravity field.

Sound- Anything that vibrates 20-20,000 Hz

Chemical- Fuels. Petrol, diesel,food,wood,coal

Electrical-Moving electrical charges or static electricity.

Light- Anything you can see is giving off or reflecting light (non-luminous or luminous)

Thermal- Particles in an object are vibrating/ moving freely.

Nuclear- Energy stored in nucleus of an atom.

Elastic potential- Any object that when stretched or sompressed returns to its original shape.

Efficiency- This is how we measure how much of the input energy is transferred uselfully.            

           %   - Useful energy transferred    x 100                                                                  

                     Total energy input

Total energy input = useful energy transferred + wasted energy

Heat transfer

Conduction- In non metals- when heated, particles vibrate more. They collide with neighbouring particles and pass on the energy.                                                                                                  In metals- Ions vibrate more AND free electrons diffuse through the metal, colliding with more ions causing them to vibrate too.

Convection- Only works in liquids and gases. Not solids because particles need to be free to move. The particles gain energy, move faster and spread apart. They fluid becomes less dense, so it rises. Cooler fluid falls to take its place and the process repeats.

Radiation (infra-red) - Energy travelling as rays. Does not need any particles, can travel through a vaccuum (a space with no particles). Heat energy goes from hot places to cold places.

Shiny silver surfaces - Good reflectors and bad emittors of thermal radiation.

Matt black sufaces - Poor reflector and good emitters, good absorbers of thermal radiation.

Insulation

Heat in the home is lossed via walls, draughts (space underneath door) , floors, roof...

Loft insulation- often made of fibre glass (glass is a poor conductor of heat), traps air so no convection can occur, trapped air is also a good insulator, can be foil backed so it refects thermal radiation back into the home.

Double glazing- Glass is  poor conductor of heat. Air is trapped in between layers of glass, this reduces convection and conduction. Making the gap narrow reduces convection.

Cavity wall insulation-Foam filled cavity means air is trapped. This reduces convection and conduction.

Foil backed plaster board- reflects more thermal radiation back into the home.

Pay-back time

Insulation costs money to install, It also saves you money on your heating bill.

Pay-back time is the time taken to save money equivelent to the cost of the insulation.

Pay-back time = cost of work                       p.b.t = cow / as

                          Annual saving

Cost effectivness…