Apparatus
- Clamp, boss and stand
- Bench
- “v-shaped runway”
- Metre rule
- Bench
- Ball bearing
- Stop watch
Diagram
Measurements
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
Conclusion
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
- by pushing the ball bearing down the runway instead of just releasing the ball bearing from the highest point on the runway but further down
-
by releasing the ball bearing in the air on the top of the runway instead of releasing it from rest in contact with the runway floor.
Unavoidably, I encountered two anomalous results due to making some of the measurement errors mentioned before. When I plotted my graph, I realised that one of the points was much higher up in relation to the line of best fit while the other was much lower down. I named these measurements A & B.
The kinetic energy gained by the ball bearing was just more than half of the gravitational potential energy it lost for most measurement e.g. when the ball bearing was dropped from a height of 0.15 metres, it stored
18.8 × 10¯4 mJ of potential energy which transformed into 11.7 ×10¯4 mJ of kinetic energy which is just a bit more than 9.4 × 10¯4 mJ (half of the gravitational potential energy it stored).
Interestingly, for measurement A, when the ball bearing was dropped from 0.17m, it had gravitational potential energy of 21.3 ×10¯4 mJ but it didn’t gain just a bit more than 10.65 ×10¯4 mJ of kinetic energy but actually gained less than half of the potential energy it stored – 10.2 ×10¯4 mJ. The reason for obtaining this irregular result may have been that I didn’t release the ball from the highest point of the runway but a few centimetres further down. This would not have provided enough energy for it to drop down as fast as it did for other measurements because gravitational potential energy ,which the ball bearing stores, depends on height h ( E p = mgh), which is lowered in this case. Therefore, it brought a decrease in the kinetic energy which the ball bearing gained – it didn’t gain as much kinetic energy as it could have done, had it been dropped from the highest point on the runway. This is why, unlike the other measurements, it gained less than half of the potential energy it stored. Another factor which may have caused this anomalous result could have been that the height of the runway itself wasn’t set accurately – lower than it should have been so although the gravitational potential energy we calculated = mgh = 0.00125 × 10 × 0.17 would have been correct theoretically, it would have been practically inaccurate as the actual height set was less than what it should have been (0.17m) and therefore the ball bearing in reality stored less gravitational potential energy than we calculated .
On the other hand, for measurement B, when the ball bearing was dropped from 0.19m, the ball bearing had gravitational potential energy of 23.8 ×10¯4 mJ but it didn’t gain just a bit more than 11.9 ×10¯4 mJ of kinetic energy ( ½ of the gravitational potential energy) but actually gained a lot more than that. The reason for obtaining the inaccurate result would have been either pushing the ball bearing down the runway or releasing the ball bearing in air on the top of the runway instead of releasing it from rest in contact with the runway floor. Either of these reasons would have provided more energy for the ball bearing to roll down faster therefore it gained more kinetic energy than it did in other measurements when it was released from the top of the runway.
Another factor which may have caused this anomalous result can be that the timing of the ball bearing rolling along the distance of 1m was recorded incorrectly or once again, the height wasn’t set correctly – the actual height set was smaller than what it should have been and therefore the potential energy calculated was less than what the ball bearing had actually stored and therefore the kinetic energy the ball bearing gained was calculated, was more than half of the potential energy which it stored.
Finally, if I was going to do this experiment again, I would use more accurate measurement equipment to make my results more accurate. I would
- use a computerised stop watch and lasers instead of a manual one to time the ball bearing rolling across the distance of 1m.
- 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.
