phy. moving things summary

• Speed


  How fast something is travelling, measured by distance travelled and time taken
• Calculating speed

  speed = distance / time
• Mean (average) speed


  Total distance travelled divided by total time taken
• Actual speeds during a journey can be faster or slower than the mean speed
• A car travelling at 50 km/h overtakes one travelling at 30 km/h

  The relative speed of the faster car compared to the slower car is 20 km/h
• Distance-time graph


  • Steeper line = faster object/person moving
• Gradient


  Measure of how steep a line is on a graph, on a distance-time graph it gives the speed
• Calculating gradient


  gradient = change in distance / change in time
• Lever


  A simple machine that can be a force multiplier or a distance multiplier
• Pivot/Fulcrum


  The point around which a lever rotates
• Moment


  The turning force on an object around a pivot, measured in newton metres (N m)
• The longer the distance, the greater the moment</b>
• When an object is balanced, the anticlockwise moment is equal to the clockwise moment
• Simple machines


  • Levers, ramps, pulleys - force multipliers that require greater distance moved
• Work

  Force x distance moved in the direction of the force, measured in joules (J)
• The box stores the same amount of gravitational potential energy whichever method is used to lift it, due to the law of conservation of energy