Energy Conservation and Efficiency

The most important rule in physics is that energy cannot be created or destroyed - it can only be transferred from one form to another. This is called the law of conservation of energy, and it explains why perpetual motion machines are impossible.

When energy moves through systems, some always gets dissipated (lost to the surroundings). Think about a printer - it receives electrical energy from the power station and converts it to kinetic energy in its moving parts. However, some energy is wasted as thermal energy through heating, which is why printers get warm.

You can reduce unwanted energy transfers in clever ways. Hot water tanks need proper insulation to prevent thermal energy loss. Car engines use lubrication to reduce friction between moving parts, stopping energy being wasted as heat.

Efficiency tells us how good a system is at converting input energy to useful output energy. The formula is: efficiency = useful output energy ÷ total input energy. More aerodynamic lorries are more efficient because they waste less energy fighting air resistance.

Key Point: In any closed system, the total amount of energy always stays the same - it just changes form!

Energy Stores and Calculations

A system is simply an object or group of objects that we're studying. Energy constantly changes between different stores within systems, and you need to spot these changes.

When a football is kicked upwards, its kinetic energy decreases as its gravitational potential energy increases. A squash ball hitting a wall converts kinetic energy into elastic potential energy. Cars accelerating turn chemical energy from fuel into kinetic energy.

The maths behind energy stores is straightforward once you know the formulas:

• Kinetic energy = ½ × mass × speed² (measured in joules)
• Elastic potential energy = ½ × spring constant × extension²
• Gravitational potential energy = mass × gravitational field strength × height

Specific heat capacity is the energy needed to heat 1kg of material by 1°C. The thermal energy equation is: change in thermal energy = mass × temperature change × specific heat capacity.

Power measures the rate of energy transfer - how quickly energy moves. Power = energy transferred ÷ time, measured in watts. An 8W LED bulb uses far less energy per second than a 28W halogen bulb whilst producing similar brightness.

Remember: These energy calculations appear frequently in exams, so practice substituting values into the formulas!