power & work done

• POWER:


  • The RATE at which energy is being TRANSFERRED
  • OR the rate at which WORK is being done.
• Power (Watts) = Energy transferred (Joules) / time taken to transfer that energy (secs)
• Power (Watts) = work done (Joules) / time taken (secs)
• • One Watt is the power from an energy transfer of one Joule per second.
  • If a device is rated at 1 Watt, it means that it transfers energy at a rate of 1 Joule per second.
• If both devices lift the same weight to the same height, the one that does it faster has a HIGHER POWER because it TRANSFERS energy at a FASTER rate.

  
• The motor in scooter B has a higher power, since both motors have the same efficiency scooter B will have a greater kinetic energy.

  
• Both scooters can be ridden for 20 minutes before the battery needs recharging

  The battery in scooter B has a greater store of chemical energy.

  
• • weight lifted
  • height lifted

  
• Reasons for taking repeat readings in an investigation:

  • calculate a mean
  • spot anomalies
  • reduce the effect of random errors

  
• As speed increases, the efficiency increases, but appears to reach a limit.

  
• The main way the motor is likely to waste energy is by heating the surroundings.

  
• When the total power input to the motor was 5 W, the motor could not lift the 2.5 N weight:

  The efficiency of the motor is 0%

  
• Work / Work done:

  A measure of the energy transferred, when a force is used to move an object by a certain distance.

  
• If a car was pushed down the road.

  • Then the energy that was required would be the work done as it's moved a certain distance.

  
• If electrical energy was transferred from a plug socket to your phone.

  • It would be "energy transferred".
  • As there’s no force or movement involved.

  
• Work done (Joules) = Force (newtons) x distance along line of action (metres)