I am going to investigate what the effect of masses have on the movement of a margarine tub when it's fired by an elastic band.

GCSE Science

By Giovanni Berzuini

10sc8

Aim:

I am going to investigate what the effect of masses have on the movement of a margarine tub when it’s

fired by an elastic band.

Plan:

I’m going to measure the distance travelled by a tub, when different weights are put in it. I will have to set

up the experiment in a very accurate way, since to obtain reliable evidence some preliminary precautions will have to be taken. I conducted a trial experiment to get a beginning idea of the proceeding the experiment. I realised that in the planning of my experiment I hadn’t taken account of some factors, which would have made harder the procedure. I realised that when I pulled back the elastic, in order to fire the margarine tub; the stool moved making it hard to fire precisely the tub. This is because the force exercised on the elastic was transferred onto the stool, moving it. I consequently decided that a second agent force had to be exerted to balance out the force exercised to pull the elastic band, so that the stool would remain still. By applying a pressure upon the stool, exercised by my partner, we found out that we could carry out the experiment fairly. Another unexpected factor that we didn’t take account of, was the method in which the margarine tub was going to be fired, we found out, after a series of trials, that the tub would travel further if in direct contact with the elastic band before the firing. I realised that the less space there was between the elastic band and the tub, the bigger the amount of kinetic energy transferred to the tub, and the bigger the amount of movement energy changed. This is because if the elastic band has to travel through a bigger amount of air, and the more air it has to travel through, the more energy molecules will be dispersed into it.

We also had to decide a suitable range of measurements to be taken, in order to achieve the clearest results that we could. We decided to use a range of weights that went from 1 to 7 grams. We felt that it would, for this case, provide clear enough results for the understanding of the pattern of the experiment.

Method:

For the outcome of this experiment the following apparatus will have to be used:

Stool the elastic band will be tensed onto the stool, and used to fire the tub
Elastic band will fire the margarine tub
Rulers to measure the distance travelled by the tub
Masses from 1 to 7 g. will be put in the tub
Margarine tub will be the object fired

I will set up the stool in an appropriate way, ready for the firing. My partner will exert a ...

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For the outcome of this experiment the following apparatus will have to be used:

Stool the elastic band will be tensed onto the stool, and used to fire the tub
Elastic band will fire the margarine tub
Rulers to measure the distance travelled by the tub
Masses from 1 to 7 g. will be put in the tub
Margarine tub will be the object fired

I will set up the stool in an appropriate way, ready for the firing. My partner will exert a pressure on it to keep it still.

I will place the margarine tub next to the elastic band, before the firing takes place. This will assure a better energy transfer between the elastic band and the tub.

I will add one mass (measuring 1 gram each) each firing, going up to 7 grams.

I will measure with rulers the distance travelled by the tub. I will repeat the experiment 3 times, in order to get appropriate and accurate results. I will also make an average of the results.

Hypothesis:

I predict that the more weights I put into the margarine tub, keeping the external force exerted constant, the less far it will travel, since a bigger amount of energy has to be applied to move a bigger mass. I also predict that the graphical representation of my experiment will be a curve, since the weight in the tub and the distance is two inversely proportional variables. And this type of correlation is represented so.

Scientific reasoning:

An object to which energy is applied unless it is acted upon from external forces, will keep on travelling at constant velocity, is what states Newton’s first law of motion. Therefore if our margarine tub wasn’t acted upon from external forces would travel forever. The fact that at a certain point stops implies that there are forces, which act upon it. The force, which causes the tub to slow down, is called friction: the friction between the tub and the molecules of air through which he travels. These molecules of air exercise a resistance to the moving body, and the opposite friction, gradually balances the energy transferred to the tub at the start, out. If we were to carry out this experiment in outer space, once energy is given to the tub, the tub would travel forever at constant velocity, until it would make contact with an obstacle. This is because in outer space there is no air, and consequently no friction can exist. Also the friction between the tub and the surface, upon which the object is travelling on, affects its motion. Again we realise that it’s all a matter of balance: the two balanced forces in consideration are the weight of the margarine tub and the support force of the ground. When weights are added into the tub these two forces become unbalanced as the weight has increased. Friction between the ground and the tub occurs, and the object gradually loses his movement energy and slows down. Before I can go deeper in my reasoning I have to define exactly what force, mass and acceleration are: acceleration means change in motion which is equivalent to the change in velocity, which as Newton’s first law of motion suggests, can only happen if the object is acted upon from an external force. The mass of an object is the quantity of matter it contains, which is determined by the numbers of atoms and molecules in it. The force is an influence exerted on an object, which results in an acceleration of such object. It seems reasonable that the external force exerted, in our case from my partner, is directly proportional to the acceleration of the object, in our case the margarine tub; as suggested by Newton’s second law of motion:

a ∝ net F

When: a= acceleration

Net f= external force

It now, also seems reasonable the fact that the acceleration, being directly proportional to the force, is inversely proportional to the mass as again Newton’s second law of motion suggests:

A ∝ 1/m

Or in equation form:

a= net F/m

I am able to represent mathematically my reasoning. In order to do this I am going to assign to each variable a random number. If, for example we had to find out the acceleration of an object of mass 2 g.

Which was by an external force of 10 Newton’s, by using the equation above we would figure out the answer is 5.

a= 10/2

a= 5

If we used an object with a bigger mass e.g. 5, keeping constant the external force exerted we would notice the acceleration has diminished to 2.

a2= 10/5

a2= 2

This proves that acceleration is inversely proportional to mass. Now I will also prove that the acceleration is directly proportional to the external force exerted. I’ll change the external force exerted to 20 N, keeping the mass constant.

a= 10/2 a2= 20/2

a= 5 a2= 10

This proves that with the increase of the external force, keeping the mass constant, the acceleration increases as well. Therefore if the acceleration increases the space covered will be bigger. Therefore if, keeping the external force constant, and increasing the mass, the margarine tub will travel less.

Fair test:

In order to make the experiment a fair test, I will have to keep some factors constant:

The elastic band should always be pulled back with the same amount energy, in every repeatings of the experiment. In order to do this the force must be exerted always by the same person. Since with the energy exerted to pull the elastic band also the stool is very likely to move, a balancing force must be applied upon it, in order to keep it still, without altering the results.
We also have to make sure the elastic band doesn’t get denatured, since during the course of the experiment it will be exposed to strong forces for various times.
I would also have to be careful no damage gets done on the margarine tub, which could be likely, since its going to carry weights during journey.
I would make sure that the tub is always fired in the same way: directly in contact with the elastic band before the firing, an alteration to this procedure would denature the results.

Results table:

Conclusion:

My results match my prediction: as more masses are added into the tub the less it travels. Also my opinion about the graphical representation of my results was right. Since the two variables that were put in the graph were inversely proportional, a curve could have been the only possible representation. All the points in my graph are even, for which nearly a perfect curve was managed to be plotted. Being the mass inversely proportional to the acceleration, as proven by Newton’s second law of motion, the mass is also inversely proportional to the distance travelled. The precise reason of this being is that an unbalance is created between two forces when masses are added to the tub. The two forces in consideration are the weight of the tub and the ground support. By adding masses the weight of the tub rises, there will be more friction between the tub and the forces, which will cause the tub to move slower and therefore to travel less.

Evaluation:

I retain that that I have conducted my experiment in a reasonably fair way. I tried to make my experiment fair in many ways: I attempted to keep constant the external force exercised; in order to do this the same person had to pull back the elastic band in each trial of the experiment. This can assure a fairly accurate outcome of the results, since the amount of energy exercised each time, should have been reasonably constant. Also we used the same firing procedure each time, that as we found out, makes the tub travel further. The accuracy with which we applied this procedure cannot be entirely verified, which will always leave us with a doubt on whether the experiment would have gone differently, but still if the efficiency of our procedure wasn’t exactly the same each time, the results couldn’t have been enormously altered. Overall though, I’m sure we have carried out the experiment in a fair way, because the results give us a clear idea of the pattern of the experiment. There are ways in which I could have improved my experiment: I could have made sure that the force applied to the tub was exactly constant each time, by using appropriate apparatus to fire the elastic band. Unfortunately we do not dispose of such equipment, therefore what we done was the best that could be done. By using more technical equipment I also would have made sure that the technique in which the tub was fired was more efficient. I would change the elastic band after each firing, to make sure it maintains in perfect condition.