Physics paper 1

• Cars, buses planes, and ships all use fuels as chemical energy stores. They carry their own fuel, Electric trains use energy transferred from fuel in power stations
• Electricity transfers energy from the power station to the train
• Chemical energy stores


  Fuels, foods, or the chemicals found in batteries. The energy is transferred during chemical reactions
• Kinetic energy stores


  The energy an object has because it is moving
• Gravitational potential energy stores

  The energy stored in an object because of its position, such as an object above the ground
• Elastic potential energy stores


  The energy stored in a springy object when you stretch or squash it
• Thermal energy stores


  The energy a substance has because of its temperature
• Energy transfers in a torch

  The torch's battery pushes a current through the bulb, this makes the torch bulb emit light and also get hot
• Energy transfers when an electric kettle boils water

  The current in the kettle's heating element transfers energy to the thermal energy store of the water and the kettle
• Energy transfers when an object is thrown into the air

  The object's kinetic energy store decreases as its gravitational potential energy store increases
• Energy transfers when an object starts to fall freely

  The object's gravitational potential energy store decreases as its kinetic energy store increases
• Energy transfers when an object hits the floor

  The object's kinetic energy store is transferred by heating to the thermal energy store of the object and the floor, and by sound waves moving away from the point of impact
• Energy transfers on a roller coaster

  As the roller coaster climbs an incline, its gravitational potential energy store increases. As it descends, its gravitational potential energy store decreases and its kinetic energy store increases. Some energy is also transferred to the thermal energy store of the surroundings by air resistance and friction, and some energy is transferred by sound waves
• Energy transfers in a pendulum

  As the pendulum swings down and towards the centre, its gravitational potential energy store decreases as its kinetic energy store increases. As the pendulum moves upwards and away from the centre, its gravitational potential energy store increases as its kinetic energy store decreases
• The total energy of a closed system is always the same before and after energy transfers to other energy stores within the closed system
• Energy cannot be created or destroyed
• Energy transfers in bungee jumping

  When the rope is slack, energy is transferred from the gravitational potential energy store to the kinetic energy store as the jumper accelerates towards the ground. When the rope tightens, the jumper's kinetic energy store decreases and the rope's elastic potential energy store increases as the rope stretches. After reaching the bottom, the rope recoils and pulls the jumper back up, transferring energy from the elastic potential energy store of the rope to the jumper's kinetic energy store
• The bungee jumper doesn't return to the original height because some energy was transferred to the thermal energy store of the surroundings by heating as the rope stretched and then shortened again
• Work


  When an object is moved by a force, work is done on the object by the force. The amount of energy transferred to the object is equal to the work done on it
• Very few people can manage to pull a lorry with a force of 2000N over 40m
• Experiments to calculate work done

  Drag a small box a measured distance across a rough surface, repeat with two rubber bands wrapped around the box
• Work done to overcome friction is mainly transferred to thermal energy stores by heating
• Energy transfers when rubbing hands together

  Your muscles do work to overcome the friction between your hands, the work you do is transferred as energy that warms your hands
• Energy transfers when braking a vehicle

  Friction between the brake pads and the wheel discs opposes the motion of the wheel, the force of friction does work on the brake pads and the wheel discs, transferring energy from the kinetic energy store of the vehicle to the thermal energy store of the brake pads and the wheel discs
• Energy transfers when a meteorite enters the Earth's atmosphere


  Friction caused by air resistance acts upon the meteorite, transferring energy from the meteorite's gravitational potential energy and kinetic energy stores to the meteorite's thermal energy store, causing it to heat up
• Astronauts on the Moon can lift objects much more easily than on Earth because the gravitational field strength on the Moon's surface is only about a sixth of the gravitational field strength on the Earth's surface
• Kinetic energy


  The energy an object has because of its motion, depends on its mass and speed
• Investigating changes in kinetic energy stores


  Release a ball on a slope, measure the decrease in its gravitational potential energy store, and the increase in its kinetic energy store as it travels a measured distance
• The greater the height drop, the faster the speed, so the kinetic energy store increases if the speed increases
• The kinetic energy store of the ball increases if the speed increases
• When the height drop is increased by four times from 0.05 m to 0.20 m, the speed doubles
• The height drop is directly proportional to the speed squared, or (speed)


  The ball's kinetic energy store is directly proportional to the square of its speed
• Kinetic energy equation


  Kinetic energy, E = 1/2 x mass, m x speed^2, v^2
• Elastic potential energy


  Energy stored when a spring or rubber band is stretched
• Elastic potential energy equation

  Elastic potential energy, E = 1/2 x spring constant, k x extension^2, e^2
• Friction in machines always causes energy to be wasted
• Wasted energy is dissipated (spreads out) to the surroundings
• Useful energy is eventually transferred to the surroundings too
• Efficiency


  Useful output energy transferred by the device / Total input energy supplied to the device
• No device can be more than 100% efficient