The same ball must be used for each test. If not the size of the ball could speed up or slow down the average speed of the same ball.
The same track must be used each time. If not the different tracks could have a rougher or smoother surface from each other and this may affect the speed of the marble/ball bearing once reached the floor.
Before timing each test the distance measured and timed at the end of the curtain rail must be the same each time you do it.
It must also be done in the same place to make sure that the air resistance is the same.
All these aspects must be undergone for it to be a successful experiment.
Predication and Scientific Knowledge
My prediction is that the higher the curtain rail at the beginning the faster the marble/ball bearing will travel along the floor and the further it will travel along the floor. The lower the curtain at the beginning the slower the ball will travel because there isn’t as much gravity forcing it along the rail.
On a rollercoaster for example there is Gravitational Potential Energy at the top of a drop which converts into Kinetic Energy when it reaches the bottom of the drop and slows down.
Gravitational = mass x height x gravitational Field Strength
Potential Energy
Kinetic Energy = ½ x mass x speed 2
There is also transferred into heat energy and sound energy. But then if we forget about the laws of friction and the energy given off from friction both Gravitational Potential Energy and Kinetic can be equal.
m g h = ½ m v 2
g h = ½ v 2
If the height changes on one the velocity will changes to be equal as well.
Method:
To find the speed of the marble/ball bearing travelling along the floor it will have to be timed over a certain distance. The distance should be accurate and reasonable to be able to get a good time in. It should be 2 or 3 metres. Preferably 3. It should be measured from five heights and timed on each one. This should be done at least 3 times to get a good average and set of results that you can work with. The range of heights need to be equally set apart. In this case it should be 10cm, 20cm, 30cm, 40cm, and 50cm. The times need to be recorded from when the ball leaves the curtain rail to where the 3 metres is finished. All results must be recorded.
Preliminary Experiment:
In our preliminary experiment we found that Gravitational Potential Energy converts into Kinetic Energy once at the bottom. The marble/ball bearing gradually slowed down as it travelled along the floor.
Another thing on the preliminary experiments was that once the ball had fell down the bottom and up the other side of the curtain rail and reversed in couldn’t reach the same height as the start because the marble/ball bearing has lost most of its Gravitational Potential Energy and therefore can’t turn it into Kinetic Energy anymore.
The Obtaining
Average Time (Secs) = All 20 cm results added / 3 (the number of results)
Speed (m/s 2) = 2 metres / average time
Analysis
Test 1
Test 1 results showed me that the higher the curtain rail at the beginning point the faster the ball bearing/marble travelled over the 2 metres when it came off the curtain rail. The results for the 20cm and 40cm heights had a large time between them compared to the 60cm and 80cm heights. The rest are all approximately the same time apart.
Test 2
Test 2 results showed me that the higher the curtain rail at the beginning point the faster the ball bearing/marble travelled over the 2 metres when it came off the curtain rail. The results for the 20cm and 100cm heights had quite a bit of time between Test 1 and Test 2. The rest are all approximately the same time apart.
Test 3
Test 3 results showed me that the higher the curtain rail at the beginning point the faster the ball bearing/marble travelled over the 2 metres when it came off the curtain rail. The results for the 20cm and 40cm heights had a large time between them compared to the 60cm and 80cm heights. The rest are all approximately the same time apart.
Average of the 3 Tests
The averaged results have quite similar times between each one.
The graph is in positive correlation and shows that the speed increases the higher the curtain rail started off at. Obviously at no height there will be no speed unless there is another force acting upon the ball bearing/marble. At 80cm the average on the graph shows up to be an anomaly. It’s not far out of the correlation but does not fit in fully like the rest of the results. There are split seconds between each height. It shows my prediction.
My prediction was that the higher the curtain rails beginning point the faster the ball bearing/marble will travel over 2 metres. I also said that Gravitational Potential Energy also gets converted into Kinetic Energy as it reaches the bottom.
Therefore the Gravitational Potential Energy and Kinetic Energy should be equal if there weren’t any interference. The length of the track also plays a part. But the biggest interference for energy lost would have been friction and heat as well as sound while the ball bearing/marble was travelling down the curtain rail. There has been a massive reduction in energy in this instance.
g h = ½ v 2
10 x 20 = ½ 1.2 2
200 = 0.72
However in this case there were obviously factors that interfered in this investigation. Air resistance would have played a part with the size of the ball bearing/marble as well as its weight.
Evaluation
I think this experiment was definitely scientifically worth it because it proves that there are factors, which effect the speed of a ball bearing/marble over a distance after dropping from a certain height. Height is the biggest factor in this case as we proved in the results the higher the ball bearing/marble is dropped from the faster the ball travels in a quicker time. I achieved a fairly good set of results. The 3 tests for each one had roughly the same time for every time it was tested. Therefore the average for each height was a good approximation. Within the whole set of results the height where the ball bearing/marble was dropped at 80.00cm seemed to be an anomalous result. It increases again after the rest of the result decrease so it goes out of sequence. This investigation was not totally reliable because there were friction differences from when the ball bearing/marble left the curtain rail and travelled on the floor. They are two totally different surfaces and the floor could have had things on which would have caused more friction than it should have had. Unwanted sticky substances could have stuck onto the equipment, which might have slowed the ball bearing/marble down. However, as well as this the equipment used wasn’t scientific enough so the time could have been .seconds out. In the place of this equipment a computer sensor could have been used, so when the ball bearing/marble passes through a strip sensor a stopwatch on the computer stops. It does this for every distance you want it to time for. There could be a few strip sensors on this route. This therefore doesn’t need to be tested as many times because it is more thorough and accurate than by a hand stopwatch. These sets of results could be expanded so that the average is more of an exact average because with only three attempts and if one result turns out totally different to the rest the average could cause an anomaly. To improve the accuracy the stopwatch could be put to more decimal places. There could have been more tests at each height to get more of an average. You could use the full equation of Gravitational Potential Energy by weighing the ball bearing/marble before the investigation and putting it into the mass. This will give a more accurate answer that equals the Kinetic Energy.
Justine Gray
10.3
Mr Bendall
Physics