The law of energy states that, ‘energy cannot be made or destroyed but it can be changed from one form into another or transferred from one place to another’. Tension is put on the elastic band when it is pulled, and by virtue, the elastic band is provided with elastic potential energy, ready to be released when it is liberated. When it is released, as the law stated, the elastic potential energy is changed into kinetic energy when it comes into contact with the margarine tub and it therefore moves due to this transfer of energy from the elastic band.
However, there will be forces working against the tub to try and slow it down and make it stop. The main force is friction which will occur between the base of the tub and the surface of the Lino. As a result, some of the kinetic energy transferred on the tub will be changed to heat energy as the temperature between the surfaces increase. Similarly, air resistance will transfer some of the kinetic energy left into more heat energy as the air particles collide with the front of the margarine tub. This process will carry on to the point where all the kinetic energy has been transferred or changed and the margarine tub has no more kinetic energy left. As a result, the tub will decelerate to the point where it stops.
When the elastic band is pulled due to the force applied by the hand, when it is released, the elastic band will come into contact with the stationary tub and the force will push the tub and cause it to accelerate. Newton’s second law clearly states that; a force exerted on an object of mass (M) will cause the object to accelerate (A). This is illustrated in the following formula:
F= M X A
For an object to accelerate, a force has to be applied for it to move. The elastic band is providing the force for the tub and as a result, it accelerates.
Prediction-
As the force applied on the elastic band increases, the distance travelled by the tub will become greater.
Linking prediction with theory-
The greater the force applied on the tub, the greater the tension on the elastic band and therefore there is more elastic potential energy transferred so more kinetic energy drives the tub forward and it goes a greater distance.
Basic method-
To prove my prediction correct, I will conduct a fair test where I will be testing and measuring how far the margarine tub travels depending on the tension and force applied on the elastic band. I will generate 3 results for each force and they have to travel within 5cm distance of each other. To aid me in this investigation I will require the following apparatus:
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Write down the results obtained in a table and generate averages. These averages will be used to plot a line on a graph.
I am predicting that my line on the graph should look something like this:
Detailed method-
In this investigation, there will be variables that I will have to change and ones that are to be kept the same throughout. There are 6 variables that are likely to effect the investigation, these are; the force applied by the hand on the elastic band, the surface area of the base of the margarine tub, the shape of the margarine tub, the surface area of the front of the margarine tub, the floor surface used and the mass of the tub. Some variables will be kept the same, for example, the floor surface used, however only the force applied by the hand on the elastic band will changing throughout the experiment. I n this investigation, our aim is to measure the force applied by the hand on the elastic band in Newtons and the distance travelled by the margarine tub in cm.
It is important to keep the other variables the same to make this a fair test. The floor surface I used throughout the experiment was Lino. I must use Lino when repeating the experiment because if I changed the floor surface and used carpet, then the amount of friction occurring will change. If I suddenly used carpet, then the rougher surface will increase the amount of friction and more friction will result in the margarine tub decelerating faster so the distance will also decrease. This will effect my results as I would be getting anomalous results as the distance would be decreasing. Similarly, if I changed my floor surface to a polished wood, then the friction will decrease between the tub and the floor and the margarine tub will travel further due to there being less friction affecting the distance travelled.
The mass of the tub must always be kept the same because the acceleration rate will change. For example, if the margarine tub was weighed down more and therefore the distance travelled will decrease. By contrast, is we made the tub lighter, it will travel further and we would expect the distance to greatly increase.
The tub that I use must be the same tub that I use for all my experiments because a change in the shape of the tub would mean that it would produce a different air resistance quantity. If it was more stream-lined, it would be more aerodynamic and therefore less air resistance would affect it so it will travel further. If it was larger, it would collide with more air particles and therefore it will slow down faster and the distance would be smaller.
The shape of the tub can also effect the surface area of the base of the tub and the surface area of the front face of the tub as well. If the surface area of the front face of the tub increased, there will be more air particles obstructing the tub and therefore it ill loose more kinetic energy faster as the particles heat up. If the front surface area decreased in size, less kinetic energy will be transferred meaning that more can be used to drive the tub forwards and so the distance will increase as a result. Likewise, if the surface area of the base of the tub decreased, there would be less friction occurring and less of the energy being changed to heat energy because less of the surface of the tub will be in contact with the Lino. If, however, the surface area of the base increased, then the counter force, being friction, will increase as well. The larger the surface area, the greater friction occurring and the distance travelled will decrease.
The only variable that we will continually change in this experiment is the force applied by the hand on the elastic band in Newtons. This variable is the only one changing so that we can use the results to plot a graph and show us the general trend.
Anomalous results-
Anomalous results are likely to occur often during the experiments due to errors. These errors can mean that you will not necessarily obtain the exact result each time for each force, and I have had to repeat the experiment for a certain force several times before it fitted in with the 5cm distance tolerance. For example, I had to carry out the experiment roughly 5-7 times for each force. This could have been the result of not fully controlling all the variables that were meant to be kept the same. When I obtained my final result I had to generate an average for each force and plot a line graph connecting as many points as possible with the force applied in Newtons along the x-axis and the distance travelled in cm along the y-axis. I plotted the averages and drew the line along the points. This way I was able to pin-point any graphical anomalous results. A graphical anomalous result is an unreliable result that does not fit in with the general trend of the line. As a result, I had to repeat this force again. The only force in my results that I had to repeat was at 4N. I had to repeat the experiment for 4N because it generated an anomalous result. When I repeated it, I generated new results and a new average, which when plotted, fitted in perfectly with the line.
