Changes in energy

• Power is rate at which energy is transferred or used up
• Work done = force x distance moved by object
• Energy transfer occurs when work is done, such as moving an object against friction.
• Equation for distance travelled

  distance travelled = speed × time
• What eventually happens to wasted energy?

  dissipates into the surroundings
• efficiency (%) = useful output / total input × 100%
• Write down the equation which links gravitational field strength, gravitational potential energy, height and mass.

  g.p.e. = mass × gravitational field strength × height
• Momentum


  product of mass and velocity
• Calculate momentum

  P=mv

  Momentum=mass x velocity
• What has happened to the rest of the energy from a gunshot?

   Transferred into heat and sound
• The miners working in a salt mine use smooth wooden slides to move quickly from one level to another. The speed of the miner at the bottom of the slide is much less than the calculated maximum possible speed. Explain why

  work is done against friction so the slide not smooth causing energy to be transferred as heat energy of surroundings
• change in thermal energy, ∆E, in joules, J
• mass, m, in kilograms, kg
• • specific heat capacity, c, in joules per kilogram per degree Celsius, J/ kg°C
• • temperature change, ∆T, in degrees Celsius, °C
• If a large amount of energy is required to heat up a substance, then its specific heat capacity will be very high
• If a small amount of energy is required to heat up a substance, then its specific heat capacity will be very low.
• If two objects have the same speed, the heavier object has more kinetic energy.
• If two objects have the same mass, then the faster moving object has more kinetic energy.