Key Variables
The things that could affect my experiment are:
- The Surface (friction on different parts of the table)
- The position I pull the tub against the elastic band.
To try and control these things I will try to put the tub in the same position on the elastic band and keep the experiment on the same desk. Although this doesn’t control the things very well, it is the best that can be done in the classroom.
Prediction
I expect that as the distance the tub is pulled back increases, the further the box will go when propelled forward.
This is because more of a force will be exerted on the tub making the tub travel further along the desk, at a faster speed.
So the graph of results should look something like this:
I think this because as the force on the tub increases, the speed will increase quicker, meaning the distance the tub travels further each time, increases more.
Preliminary Tests
After doing preliminary tests I have noticed that the tub does not begin to move, until it is pulled back 4cm. I also noticed that when it got pulled back over 12cm the tub spun while travelling along the desk, making it not fair to measure properly.
After realising this I have decided that instead of starting at 2cm and increasing the distances by 2cm each time, I will start at 4cm and increase the distances pulled back by 1cm each time all the way up to 12cm.
Results
Analysis
My graph shows me that as the elastic band was pulled back further and further, the further the tub travelled.
This can clearly been seen by the way the results curve upwards steeper and steeper. Meaning that the each time the tub was pulled back further, it didn’t just increase in distance the same amount each time, otherwise it would of produced a straight diagonal line going up. Instead it gains in distance from the previous result by a bit more each distance pulled back, creating the upwards curve on the graph.
This happens because energy from me transfers to the elastic band, by me pulling the tub back against it. The potential energy in the elastic band is then released as kinetic energy when I let go of it, giving the tub kinetic energy moving it forward. Meaning the more work done by me, the bigger the force on the tub from the elastic band. Which then means the distance the tub travels increases.
In my prediction I thought that:
As the force on the tub increases, the speed will increase quicker, meaning the distance the tub travels further each time, increases more.
After doing the experiment I now know this is correct and that the predicted shape of the graph I drew, is also correct. So my results match my prediction very well.
Evaluation
On my graph there only seems to be 3 odd results. But even thought they are odd, they aren’t very far off of norm.
They are slightly out, but this is possibly because of the position of the elastic band on the tub, or the smoothness of the surface. As the surface was only the school table, which I know is not perfectly smooth, it is most likely the surface, which is to blame for the slightly off results. I tried to make the results better by using averages, which most likely did help to make the results better, but even with the averages the results still were slightly off.
If I could do the experiment again, I would use a much smoother surface, which has no bumps in it like the school desks. I would also repeat the distances more than 3 times, for example 10 times, and then find the average, giving a much better result.
A problem that I had when doing the experiment was that when I went to stretch the elastic band across the chair legs it wasn’t big enough. Because of this I had to tie two elastic bands together which then could reach across between the two legs. So if I did the experiment again, I would also probably get a larger elastic band, so that two don’t have to be tied together.
Further work that I could do is to change the mass in the tub; instead of changing the distance the tub is pulled back. For this further experimentation I have made a plan, which you can see over the page.
FURTHER EXPERIMENTATION
Plan
Aim
To see how the distance, a margarine tub travels, changes, as the weight inside the tub changes.
Diagram
Equipment
- Elastic Band
- Weights
- Margarine Tub
- Graph Paper
- Stool
- Table
- Ruler
- Set Square
- Selotape
Method
After the equipment is set up, I will put 50g of weights in the margarine tub. I will then pull the tub backwards against the elastic band so the back of the tub is at the 8cm. I will also use the lines on the graph paper to make sure the tub is straight.
I will then release the tub, letting it get propelled forward by the elastic band. When the tub stops moving, I will measure the distance it has travelled using the metre rule and a setsquare to make it more accurate.
I will record the distance it has travelled, then repeat it 2 more times. So that an average can be found.
Once I have done this I will repeat it all again, but instead of 50g in the tub, I will change it to 100g, then 150g, then 200g, adding 50g each time until the weights in the tub equals 500g.
Fair Test
To make the investigation a fair test, I will not change these things:
- Surface
- Margarine Tub
- Distance pulled back
- Elastic Band
The only thing that I will change is the amount of weights in the margarine tub.
Key Variables
The things that could affect my experiment are:
- The Surface (friction on different parts of the table)
- The position I pull the tub against the elastic band.
To try and control these things I will try to put the tub in the same position on the elastic band and keep the experiment on the same desk. Although this doesn’t control the things very well, it is the best that can be done in the classroom.
Prediction
I expect that as the weight inside the tub increases, the distance the tub travels will get less and less.
I think that this will happen because the friction between the table and the bottom of the tub will increase, as the mass of the tub increases. As this friction increases it means that to move the tub as far as the previous go, the tub will have to be pulled back further against the elastic band. But as the distance pulled back is kept the same, it means the tub wont travel as far as the previous go.
So the graph of results should look something like this:
