P1

Energy stores

Thermal

Kinetic

GPE

Elastic potential

Chemical

Magnetic

Electrostatic

Nuclear

Energy is transferred mechanically (doing work), electrically (moving charges), by heating or by radiation (light and sound)

Systems

A single object or a group of objects

Closed system - matter nor energy can leave or enter. Net change is always 0

Work done

Same as energy transfer

Work can be done when current flows or by a force moving an object

Falling objects also transfer energy

When a ball is dropped from a height it is accelerated by gravity - the gravitational force does work

As it falls, energy from the objects gravitational potential energy store is transferred to kinetic.

Kinetic and potential energy stores

Anything that is moving has energy in its kinetic energy store - transferred to the store when speeding up and transferred away when slowing down

Energy in the kinetic energy store depends on mass and speed. Greater mass the faster it goes the more energy in its kinetic store

Energy in GPE depend on mass, height and strength - higher the object the more energy in GPE

Specific heat capacity

Different materials have different heat capacity

More energy needs to be transferred to the thermal store to raise the temperature than other

4200J to warm water by 1 degree but 139J to raise mercury

Definition - amount of energy needed to raise the temperature of 1kg by 1 degrees

Practical

Block of material with 2 holes. Measure the mass of the block and then wrap it in insulation to reduce energy transferred to the surroundings. Water in the thermometer hole and heater in the other. Measure initial temp and then turn on heater and start stopwatch. As block heats up measure temperature every minute

Conservation of energy and power

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

Power is the rate of doing work or rate of energy transfer

Conduction and convection

Conduction is the process where vibrating particles transfer energy to neighbouring particles

  1. Energy transferred by heating is transferred to the thermal store
  2. The articles on the part being heated vibrate more and collide with each other. Collisions cause every to be transferred between kinetic energy stores
  3. Process continues until reaching the other side of the object where its dissipated

Convection is where energetic particles move away from hotter to cooler regions

  1. Happens in gases and liquids. When you heat a region of a gas or a liquid the particles move faster and the space between them increase
  2. This causes density of the region to decrease. If there is a constant heat source a convection current can be carried

Reducing unwanted energy transfers

Lubrication reduces frictional forces

Insulation reduces rate of energy transfer by heating

HAve thick walls with low thermal conductivity -slower the rate of transfer

Thermal insulation in houses - Cavity walls with foam, Loft insulation, Double glazed windows

Efficency

The less energy wasted, the more efficient the object is

Efficiency = useful power output / total power imput

No device is 100% efficient

Energy resources and their uses

Non renewable energy sources - Coal, natural gas, oil

Renewable energy sources - Solar, wind, waves, hydro-electricity, bio-fuel, tides, geothermal

Will all run out, do damage to the environment

Will never run out, less damage than non-renewables, unreliable

Wind power - noise pollution, no damage to environment, initial price is high but no maintenance prices (e.g. fuel)

Solar cells - expensive but little environment damage, can increase output on days of high demand.

Hydroelectric power - large environment impact, can raise demand

Biofuels - Carbon neutral, reliable and short time to make, costs to refine are very high, wont be enough space for human food and biofuel crops

Fossil fuels are heavily reliable but damage the environment - Greenhouse effect, open-cast mining ruins views, oil spillages, nuclear waste, acid rain