P1: Conservation and Dissipation of Energy

• P1 1) Give 5 ways energy can be stored?

  Chemical energy, kinetic energy, gravitational potential energy, elastic potential energy and thermal energy,
• P1 2) What is chemical energy stores?

  Energy transferred during chemical reactions. Stores include fuels, foods or chemicals found in batteries.
• P1 3) What is kinetic energy stores?

  Energy stored in an object because it is moving
• P1 4) What is gravitational potential energy?

  Energy stored in an object because of its position above the ground.
• P1 5) What is elastic potential energy?

  Energy stored in a springy object when you stretch or squash it.
• P1 6) What is thermal energy?

  A store of energy a substance has because of its temperature
• P1 7) What are the energy changes in a torch lamp?

  Chemical energy in battery à electric current in wires à energy transferred to surrounding (light and thermal)
• P1 8) How can you represent energy changes?

  Flow diagram
• P1 9) What are the energy transfers in an object as it falls?

  Gravitational potential energy store à kinetic energy store à energy transfer to the surroundings (thermal energy and sound waves)
• P1 10) What is a system?

  An object or group of objects
• P1 11) What is a closed system?

  A system in which no energy transfers take place our of or into the energy stores of the system.
• P1 12) What is the principle of conservation of energy?

  Energy cannot be destroyed or created.
• P1 13) What is energy measured in?

  Joules (J)
• P1 14) What is work done?

  Work is done on an object when a force makes the object move. Energy transferred = work done
• P1 15) What is work done measured in?

  Joules (J)
• P1 16) How do you work out work done?

  Work done, W (J) = force applied, F (N) x distance moved along the line of the force, s (m)
• P1 17) What happens to work done to overcome friction?

  Mainly transferred to thermal energy stores of the objects that rub together and to the surroundings.
• P1 18) A builder pushed a wheelbarrow a distance of 5m across flat ground with a force of 50N. How much work was done by the builder?

  250J
• P1 19) What happens to the gravitational potential energy stores when an object moves up?

  It increases
• P1 20) What happens to the gravitational potential energy stores when an object moves down?

  It decreases
• P1 21) How do we calculate change in object's gravitational potential energy store with weight?

  Change in object's gravitational potential (J) = weight (N) x change of height (m)
• P1 22) How do we calculate change in object's gravitational potential energy store with mass?

  Change of gravitational potential (J) = mass, m (kg) x gravitational field strength, g (N/Kg) x change of height (m)
• P1 23) Why is it easier to lift objects on the moon?

  Gravitational field strength of moon about a sixth of gravitational field strength on earth.
• P1 24) A student of weight 300N climbs on a platform that is 1/2m higher than the floor. Calculate the increase in her gravitational potential energy store?

  360J
• P1 25) A 2kg object is raised through a heigh of 0.4m. Calculate the increase in the gravitational potential energy store of the object. The gravitational field strength of the Earth at its surface is 9.8N/kg.

  7.8J
• P1 26) What does the amount of energy in a kinetic energy store depend on?

  Its mass and speed
• P1 27) How do we work out kinetic energy?

  Kinetic energy (J) =1/2 x mass (kg) x speed²
• P1 28) How do you calculate the amount of energy in an elastic potential energy store?

  Elastic potential energy (J) = ½ x spring constant (N/m) x extension²
• P1 29) Calculate the kinetic energy stored in a vehicle of mass 500kg moving at a speed of 12m/s

  36000J
• P1 30) What is useful energy?

  Energy transferred to where it is wanted in the way it is wanted
• P1 31) What is wasted energy?

  Energy that is not usefully transferred
• P1 32) What is meant by energy dissipation?

  Energy spreads out to surroundings
• P1 33) What happens to the usefulness of energy as it dissipates?

  Gets less
• P1 34) What is input energy?

  The energy supplied to an object/device
• P1 35) What is useful output energy?

  The energy that comes out that we actually want to use
• P1 36) How do we work out efficiency?

  Efficiency = useful output energy (J) / total input energy (J)
• P1 37) A light bulb with an efficiency of 0.15 would radiate 15J of energy as light for every 100J energy supplied. What is its efficiency?

  15%
• P1 38) How do we reduce wasted energy by friction?

  Lubricate moving parts to reduce friction
• P1 39) How do we reduce wasted energy by resistance of a wire?


  Use wires with as little resistance as possible
• P1 40) How do we reduce wasted energy by air resistance?

  Streamline shapes of moving objects