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Converting gravitational potential energy into kinetic energy.

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  • To investigate how gravitational potential energy in a ball bearing is transformed into kinetic energy when it is released from rest at the top of a runway and it slides to the bottom and rolls on the bench along a distance of 1 metre.  


  • As energy can’t be created or destroyed, the amount of kinetic energy the ball bearing would gain as dropped from the runway should be the same as the amount of gravitational potential energy it stored.


  • Because the ball bearing would lose energy in the form of sound as if it is released from the runway when it rolls, the input energy wouldn’t be the same as the output energy but slightly less.



  • A ball bearing is released from rest at the top of the runway and it will lose gravitational potential energy and gain kinetic energy as it rolls from the top of the bottom.
  • When it reaches the bottom it should roll along the bench at a constant speed as long as the bench is horizontal.
  • The speed, v , can be found by measuring the time it takes for the ball bearing to travel a distance of 1m.
  • If the mass of the ball bearing is m kg , then loss of gravitational potential energy = m×g×h


  • The gain of kinetic energy = ½×m×v²

(h   in metres, v    in m/s & g= 10N/ kg)


  • First, we set the apparatus shown in the diagram. After that, we set the height (h) to 5cm initially and measured this distance as accurately as we possibly could. Then we released a ball bearing at the top of the runway and as it reached the bottom, we recorded the time it rolled through a distance of 1m along the bench. We then repeated the measurement two more times to obtain an average time to make the results more accurate.
  • We then increased the height (h) in steps of about 2cm, each time taking three measurements of the time taken for the ball bearing to roll 1m along the bench. We continued this till we had obtained measurements for 10 different values of (h) – 0.05m, 0.07,m, 0.09m, 0.11cm. . . 0.23m
  • Moving on, we measured the mass of the ball bearing so we could use it in the formula   Ep = mgh  & Ek = ½mv² to calculate the loss in gravitational potential energy and gain in kinetic energy.
  • Finally, we plotted a graph of the gain of kinetic energy (½mv²) on the vertical axis against the loss of gravitational potential energy (mgh) on the horizontal axis.
  • We then observed, analysed and commented on the results we obtained.
...read more.


Metre rule Bench Ball bearing Stop watch




A graph of the gain of kinetic energy against the loss of gravitational potential energy when a ball bearing is released at the top and it reaches the bottom and roles through a distance of 1m along the table.

Gravitational Potential Energy

Kinetic Energy


Theoretically, my prediction was correct as my results supported it. The gravitational potential energy lost by the ball bearing when it rolled down the runway and onto the bench, wasn’t the same as the kinetic energy gained but slightly less, for most measurements.  This is because the ball bearing lost energy in the form of sound and heat as it came in contact with the runway sides when it was sliding downwards on to the bench.

However, the reason why not all my points don’t lie on my line of best fit was due to measurement errors while I was doing the experiment or plotting a graph. These errors would have been occurred

  • while timing the ball bearing

                 (rolling a distance of 1m along the bench) due to inconsistent

                  human reflexes,

  • by not making sure the height is set correctly
...read more.


do an experiment on more even surfaces to reduce energy being lost in the form of heat by friction when the ball bearing slides down the runway or hits the sides on the way down the runway. Take more measurements for each reading to obtain more reliable and accurate averages Be more careful and alert in measuring and timing. Have the same person operating the stop watch as different people’s have different reaction times which may not give reliable enough results to reach a firm conclusion. Do the experiment in the same environment on the same day so that changes in room temperature doesn’t affect energy transformations – e.g. when the room temperature is higher, the runway floor would become hotter and the ball bearing sliding on it would lose more heat energy by friction. Use an even more accurate metre ruler to make the timing of the ball bearing rolling along the distance of 1m, more accurate. Enlarge the distance I want the ball bearing to roll along so chances of obtaining inaccurate timing of the ball bearing is reduced. Use a smoother ball bearing so it loses less energy in the form of heat and sound when it slides along the runway floor.

...read more.

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