1/2 Fe =Л m g d
The average force is a half (5), when I am pulling back my tub to 10N, therefore 0N, will be too small, minimum and 10N will be the maximum in which I can pull back the tub. Therefore I have used 5N to complete the table, which is mid way between 0 and 10N.
I have chosen to use 0.04 as my coefficient of friction. This is because 0.04 is the coefficient for teflon on teflon, which is plastic on plastic. This is the nearest I am going to get.
My Resources
I have obtained all of my information from Advanced Physics and Advanced Physics for You (p18), What Causes Friction?
Fair Test:
To ensure that the experiment is a fair test, the only variable I will change is the mass of the tub. The fixed variables are:
- The area of the margarine tub
- The amount of energy input.
The mass of the tub and the sellotape will also be taken into consideration when writing in the table of results.
Method
After a preliminary run was carried out to find a suitable range of masses to use for this experiment, an elastic potential of 0.1M was decided and the following range was decided for the different masses: 0g - 300g in 50g masses (without including the weight of the tub). The experiment will be repeated at least twice to ensure accurate and reliable results. I am going to measure the distance travelled (M) by a margarine tub, which contains various masses (kg). Decimals will be used and the results will be recorded in a table.
For this experiment two stools will be taken and sat next to each other, an elastic band will be attached to each leg. The distance between the two stills will be 10cm, the elastic band will then be extended 10N/10cm and the point of extension will be marked using chalk. A margarine tub will then be taken and a small amount of sellotape will attach the various masses to the bottom of the margarine tub. This is too ensure a fair test, as if the masses are loose, the masses may help the margarine tub by hitting the opposite end making it move further. A variety of masses will then be placed inside the tub, which will be projected from the elastic band. The distance travelled by the tub will be recorded in a table. String will be used to measure so that parallax cannot take place to ensure accuracy.
Apparatus
- 2 Stools
- Elastic band
- Newton metre
- Chalk
- 2x 1Metre rulers
- Balancing scales
- 1 Margarine tub
- Sellotape
- 6x 50g Masses
- String
Diagram
This is a copy of the result table in which I am going to use:
The first table is the table in which I am going to use, but I am also going to use the second table to base my graph on, as it is a lot simpler.
Observing
Weight of Tub: 22.24g
Total Weight: weight of tub + mass + gravity + sellotape
Analysing
The graph shows that if the mass is doubled then the distance travelled by the margarine tub is halved, and that the more mass there is in the tub, the less it travels. I have some anomalous results, which could be due to a number of reasons:
- The stool sometimes moves,
- sometimes fingers can get in the way when the margarine tub is being projected,
- The elastic band may not have always been pulled back to the full 0.1m.
- The distance travelled by the margarine tub may not have always been measured accurately.
The line of best-fit shows that as the mass is doubled then the distance travelled by the margarine tub has decreased by nearly a half. This is because as the masses in the tub are increased, the friction/pressure between the floor and the tub also increases. This then creates an increase in heat due to friction, which is quickly lost and so causes the tub to travel a shorter distance.
Also, if the force and the pull back distance remain constant and the mass is doubled, the distance travelled is nearly halved because the elastic potential energy is converted to kinetic energy, which is then converted to heat energy:
1/2 Fe= Лmgd
A smooth curve can be seen on the graph, which is what I earlier predicted. A smooth curve can be seen because the graph shows that the more masses put into the tub, the less the margarine tub travels. Some of the frictional energy may also have been lost through sound and air resistance, as well as heat.
Evaluating
My original plan has not changed and I think that the method was good enough to produce results, but to make the experiment more accurate, the same people did the same job throughout, the tub was pulled back 10N/10cm each time and the same equipment was used.
If the experiment was to be repeated, I would not use just stools as we found out that they kept slipping because they were too light. Therefore, I would suggest using stools again but have a person sitting on each stool to make sure it wouldn't move. If this was to be done, you would have to make sure that the people who were sitting on the stool are of similar weights too make sure it remains a fair test.
Also I think when the tub was being pulled back each time, you have to ensure that before projecting the tub that each time it was being pulled back to the full 10N/10cm.
.
In our experiment we had a few anomalous results (as highlighted). This could be due to the following reasons:
- 50g masses were too light
- The stool sometimes moved
- Fingers can get in the way when the stool is being projected.
- It may not have always been projected to the full 10N/10cm each time.
- Although string was used to reduce parallax, there may have been an inaccuracy when measuring the distance.
I think it would also be beneficial to do more repeats to allow for all the anomalous results.
