The aim of this experiment is to determine whether or not energy is conserved when a ball bearing is rolled down a slope. Six weeks of preliminary work have been carried out ensuring that measurements can be taken quickly with the correct instruments needed for the measurement. Previous knowledge of energy conservation says that energy cannot be created or destroyed.
In this experiment many factors need to be considered, some need to vary, some need to remain the same.
Measurements must also be taken.
There are three factors that need to remain constant if this is to be a fair test, these are:-
Length will be measured in metres.
Time will be measured in seconds.
Speed will be measured in metres per second.
GPE and KE will be measured in Joules.
In order to carry out a fair test the same equipment will be used for each measurement, each measurement will be repeated from the same point at least twice. A constant length of track will be used. The effects of friction and sound will be taken into account as ways in which energy is lost. The height of the track will be changed as will the mass of the ball but the starting point and speed of the ball will remain constant.
Mass will have no effect on the speed of the ball bearing, if mass increases so will the weight, the weight will act on a larger amount of matter, so the two forces will cancel each other out.
If height increases so to will velocity because as height increases so will GPE, if energy is conserved then this energy will be transferred to kinetic energy giving an increased velocity.
Use scientific understanding to explain the prediction
The formula for GPE is mgh.
The formula for KE is 1/2mvï¿½.
Mass is common to both equations so it can be removed.
mgh = 1/2mvï¿½
2gh = vï¿½
20h = vï¿½
Therefore vï¿½ is proportional to h.
If h quadruples so does vï¿½ therefore v doubles.
ie. 4h and 4vï¿½
To find the value of v:- /4vï¿½ = 2v. Doubled velocity.
What measurements should be taken, and with what?
The time taken for the ball to roll from start to finish will be measured ten times at each height using a stopwatch.
How is the experiment made as accurate as possible?
The experiment is made as accurate as possible by measuring variables to the most accurate unit possible, ie. Length is measured to the nearest thousandth of a metre.
The ball is rolled down the track seven times for each height investigated, the highest and lowest readings for time are discarded and an average of the remaining five times is found.
The ball is released at the same speed and at the same start point in each experiment.
See attached sheets for graph and results tables.
The three lines on the graph seem identical within the margins of experimental error so the results show that mass has no effect on the speed of the ball and that as height increases so does velocity, this relationship is proportional as the lines on the graph are straight and pass through the origin.
What trends, patterns or relationships can be found in the results?
As the height of the track quadrupled, the velocity of the ball bearing roughly doubles, and vï¿½ roughly quadrupled, this is a direct square correlation.
The results turned out as they did because of basic scientific rules and principles. The more gravitational potential energy (mgh) an object has, the more energy will be converted to kinetic energy (1/2mvï¿½), since mass does not change the mass factors in both equations can both be cancelled out. Therefore, the energy an object has from GPE being converted to KE must have an effect on that object’s velocity.
The closer an object is to the vertical, the greater the speed due to acceleration caused by gravity, an object on a slope 40cm high will fall to Earth slower than an object on the same length slope at a height of 80cm.
The prediction for this experiment was correct, mass had no effect on the speed of the ball bearing.
Not all of the GPE was transformed into KE, only about 15% of GPE was used as KE, this means that 85% of the energy was lost as heat due to friction and as sound.
Analysis suggests that vï¿½ is proportional to h for this experiment, the results fully support this.
Mass does not continue throughout the analysis.
The graphs are identical for all three ball bearings, within the limits of error, showing mass not to be involved.
Each graph is a straight line through the origin confirming that vï¿½ is proportional to h.
Analysis shows that if metres are used the gradient should be close to twenty. If centimetres are used then the gradient should be close to 2000. This however relies on the final speed of the ball bearing being used, this experiment calculated the average speed of the ball bearing. The average speed is half the final speed so vï¿½ on the graph is only a 1/4 of its true value. Therefore the gradient should be close to 5m/sï¿½ or 500 m/sï¿½.
The actual gradient of the graph is 3?m/sï¿½.
The anomalous results occurred at the higher heights, the ball travelled down the ramp quickly and human reflexes could not stop the timer at the correct value.
To make this experiment as accurate as possible high quality equipment is needed. To eliminate air resistance the experiment would need to be carried out in a total vacuum. To reduce friction on the slope and on the ball, glass or polished metal should replace the plastic slope and the ball bearing.
To make measurements of time more accurate, computers could be used to release the ball and light gates used to give accurate timings of the ball rolling down the track. The final speed of the ball should be found instead of the average speed. Large micrometers could be used to measure lengths and highly accurate digital balances used to measure mass. This would eliminate human delays due to slow reflexes.
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