4 - Energy

• What is the principle of conservation of energy?

  Energy cannot be reused or destroyed
• What happens to energy when it is transferred to the surroundings?

  It is dissipated but total energy remains the same
• What are energy stores?

  Places where energy is stored and measurable
• What are the eight types of energy stores?

  • Chemical (fuels, food, battery)
  • Gravitational potential (lifted objects)
  • Kinetic (movement)
  • Thermal (heat)
  • Elastic (change shape)
  • Nuclear (stored in nucleus)
  • Magnetic (attraction and repulsion)
  • Electrostatic (electricity/charged objects)
• Why does friction between moving parts cause heating in machines?

  It causes waste energy through heating
• How can you reduce friction in machines?

  By lubricating the moving parts
• What happens when a current passes through a wire?

  The wire's resistance causes it to heat up
• What should you use in circuits to minimize energy loss?

  Wires with as little electrical resistance as possible
• How does air resistance affect energy transfer?

  It causes energy transfer to the surroundings
• How can you reduce air resistance on moving objects?

  By streamlining their shapes
• What is a consequence of sound created by machinery?

  It causes energy transfer to the surroundings
• How can you reduce noise from machinery?

  By tightening loose parts to reduce vibration
• What are the pathways through which energy can be dissipated?

  • Mechanical: rises in temperature through friction
  • Electrical: rises in temperature due to resistance
  • Radiation/Particles: temperature changes with IR absorption/emission
• What does work measure in terms of energy?

  How much energy is transferred
• What factors affect the work done by forces?

  Amount of force and distance applied
• What is the formula for calculating work done?

  Work done = force x distance moved
• What is the unit of work done?

  Joules
• Calculate the work done lifting a bag with a force of 8N over 420mm.

  1. 36J
• Calculate the work done stepping up a weight of 35kg over 15cm.

  0.625J
• Calculate the work done stretching a spring with a force of 7N over 300mm.

  1. 1J
• Rank the following actions from most to least work done: dragging a box, lifting a bag, stretching a spring, stepping up.

  Most work done:

  1. Lifting a bag
  2. Stretching a spring
  3. Dragging a box
  4. Stepping up (least work)
• Calculate the work done dragging a box with a force of 15N over 430mm.

  1. 45J
• What does power measure in terms of energy transfer?

  How quickly energy is transferred
• What is the formula for calculating power?

  Power = energy transferred / time taken
• What are the units for power?

  J/s or Watts
• What is the conclusion regarding energy transfer and power?

  Power indicates the speed of energy transfer