SAFETY
In order to carry out this experiment safely so as to cause no damage to any person or to the equipment, a number of points needed to be taken into consideration
The string that is attached to the trolley and the weights needs to be securely tied to both the trolley and the weights so that neither of them will work loose.
The mass at the end of the string must not be too great. If it was the 'smart pulley' system that will be used to measure and record the acceleration of the trolley would break under the pressure.
The board acting as the 'incline' must be secure to prevent it from falling over
FAIR TEST
It is important to keep the factors of the experiment constant. By doing this I will have only one variable element, which will be the mass of the weights. The components, for the experiment are as follows.
1. Mass of the Trolley The force that will be acting on the ramp must stay the same throughout and this is determined by the mass of the trolley. To control this factor I we will use the same trolley each time.
2. Friction This will slow down the speed at which the trolley travels. A way of reducing the amount of friction is by having a smoother surface and by using wheels without a rubber tyre. The surface will be kept the same throughout the whole experiment to control this quandary.
3. Air Resistance This cannot be controlled to a great extent although the aerodynamics of the trolley will be kept the same each time.
4. The Height of the Ramp This must remain constant or I would not be able to know whether the acceleration was influenced by the height or another factor. If the ramp was to be made higher it would cause a different velocity. The height will be checked using the Cosine Rule.
5. Repetition Each time the weight is changed at the end of the string, the experiment will be repeated two times so that an average result can be taken. If any of the results differ greatly from what is expected, the experiment will be repeated again.
HYPOTHESIS
I predict that when the mass at the end of the string is at its lowest weight the acceleration of the trolley will not be very great. As the mass increases so will the acceleration of the trolley as it goes up the 'hill'. The equation for this is F=ma. But as I am trying to measure the acceleration of the trolley the equation will have to be changed to A=f/m. The f. in the equation is equal to the mass of the weights at the end of the string times gravity (9.8), minus the mass of the trolley times gravity (9.8) times Sinex (x=the angle of incline of the hill is). The m=mass of the trolley plus the mass the weights on the end of the string. Another equation could be a=v-u/t, but for this I would need to find the initial velocity and subtract one from the other and that would take valuable time. I predict that the graph will look like the one below, which clearly shows that as the mass of the weights increase so, will the acceleration of the trolley. The graph will be directly proportional.
Acceleration of Trolley
Mass of Weights
Due to gravitational potential energy (GPE which is the amount of energy that an object has because it its position) the higher the object, the more GPE it has. As the trolley starts at the bottom of the ramp and goes up, GPE does not affect the velocity or acceleration of the trolley. However when the object begins to climb its GPE is converted gradually into kinetic energy (KE).
GPE = mass x g x height
Where g = acceleration due to gravity = 10m/s2
KE = 1/2 x mass x (velocity)2
LIST OF EQUIPMENT
For the duration of the experiment the following apparatus will be used:
1x Friction Free Trolley,
1x Smart Pulley,
1x Computer (for recording results)
1x Plank of wood to act as ‘incline’,
1x 2m length of String,
10x 50g Weights,
1x 30cm Ruler,
1x Calculator,
2x Stand,
2x Clamp,
2x Boss,
FACTORS THAT MAY AFFECT THE OUTCOME OF THE EXPERIMENT
1. Acceleration
In the formula F=Ma, the measure of force is in Newton’s, the mass will usually be in grams or kilograms and the acceleration will be measured in meters per second. Newton's second law of motion is more abstract than the first law. The second law includes all acceleration and is very simple to comprehend. Acceleration comes about when a force acts in some direction on a body. The larger the mass of the body, the more force is needed to accelerate it.
Acceleration= the rate of change of velocity with time. You can calculate it using the equation below:
Acceleration = velocity change / time taken for the change
The units for acceleration are a little complex. We know that velocity is in m/s. Therefore, a change in velocity must also be in m/s. Time is of course, in seconds. Together, this information gives units for acceleration of metre per second, per second. This is simplified by being written as m/s2
Naturally, objects change in velocity when slowing down. This counts as a negative change, and so gives a negative value for the acceleration. An object can easily have an acceleration in an opposite direction to its velocity. This will happen once the weights connected to the trolley hit the ground. The trolley will go up as far as possible using the KE gained and will progressively slow down. It will then descend back down the slope.
2. Gravity Force
The force of gravity is the force at which the earth, moon, or other massively large object attracts another object towards itself. By definition, this is the weight of the object. All objects on Earth experience a force of gravity, which is directed "downward" towards the centre of the earth. The force of gravity on earth is always equal to the weight of the object as found by the following equation:
Fgrav = m x g
Where g = 9.8 m/s2 (on Earth)
And m = mass (in kg).
3. Normal Force
The normal force is the support force exerted upon an object, which is in contact with another stable object. For example, if a book is resting upon a surface, then the surface is exerting an upward force upon the book in order to support the weight of the book. On occasions, a normal force is exerted horizontally between two objects, which are in contact with each other.
4. Friction
The friction force is the force exerted by a surface as an object moves across it or makes an effort to move across it. The friction force opposes the motion of the object. For example, if a book moves across the surface of a desk, then the desk exerts a friction force in the opposite direction of its motion. Friction results from the two surfaces being pressed together closely, causing intermolecular attractive forces between molecules of different surfaces. As such, friction depends upon the nature of the two surfaces and upon the degree to which they are pressed together.
PLAN
The experiment will be carried out as follows:
1. Firstly everything will be checked to make sure it is all correct and meets the necessary criteria. I will ensure that the experiment will be carried out in a safe and fair way.
2. Once this has been done the friction free trolley will be placed in a marked spot. This spot will be the same every time so to make it a fair test. The string will then be tied on to the trolley and the weights.
3. The weights will then be released and the smart pulley will transfer the data on to will record the data on the computer.
4. This will be repeated another three times. If the results look incorrect the experiment will be repeated again and an average taken.
5. Another weight will then be added according to the table and the experiment will be repeated another three times or more as necessary.
I believe that the way I plan to carry out the experiment is good because there are not many scientific factors that could affect how the experiment changes as the variable does. In using the smart pulley system the results that I collect should be as precise and accurate as possible.
DIAGRAM TO SHOW HOW I WILL SET UP THE EXPERIMENT
RESULTS TABLE FOR THE EXPERIMENT
ANALYSIS OF EXPERIMENT
The experiment was carried out as stated in the plan. No problems were encountered during the experiment.
RESULTS
From the results table and the graph I have concluded that the mass of the weights on the end of the string is directly proportional to the acceleration. However the doubling of the weights more than doubled the rate of acceleration e.g. 100g = 0.383, 200g = 1.65.
EVALUATION
I believe that the experiment went very well I did not discover any major difficulties, and feel that I achieved the best results when considering the available equipment. However given more time and better apparatus to measure the velocity of the trolley, it could have achieved greater accuracy. Possibly a centisecond timer or millisecond timer which have the sensitivities to be able to measure the velocity of the trolley up to 1/1000s would have guaranteed better accuracy. Nevertheless I am pleased that I decided to use the smart-pulley rather then the ticker timer or light gate. Even though the pulley caused friction on the trolley, it proved to be very reliable.
Taking three sets of results on each weight proved that the smart-pulley was dependable because all three of the readings were nearly identical each time. By taking this number of results also ensured that there were not any anomalous results. I can verify this because the line of best fit went through the plotted results on my graph. Plotting a rough graph as I carried out the experiment simplified matters because I was able to keep track of my results and ensure no mistakes were being made.
Given more time I would have repeated the whole experiment and would have taken 5 or more readings of each weight to guarantee that my results were indeed reliable. In conclusion, I am sure that my results show a high degree of accuracy and are dependable enough to draw a reliable conclusion.
