Physics Coursework Essay
Aim: To find out how increasing the height an object is dropped from, affects its average speed.Prediction: I predict that the higher the object is dropped from the faster its average speed. This is because gravity pulls everything down and the higher an object is dropped from, the more time it has to accelerate until it reaches terminal velocity.V=ta+u(Where V = Final Velocity, T=Time, A= Acceleration and U= Initial velocity)In addition, the heavier an object, the longer the distance it has to travel before drag equals weight. This means the object will probably never reach terminal velocity.Plan: First I will collect the equipment and use a ball of plasticine to drop through air as a freefall. I will drop the ball from heights of 30cm, 40cm, 50cm, 60cm, 70cm, 80cm, 90cm and 1m.I will use a measuring stick to measure the heights from which to drop the plasticine. I will then drop the ball from each height and record the speed by timing how long it takes to reach the floor.1. Collect equipment (see below)2. Set up metre stick along table leg3. Prepare and weigh plasticine balls, making sure they are spherical4. Hold the ball with the bottom of the plasticine just above measurement5. Drop the ball timing it with the stopwatch until the exact moment it hits the floor6. Record results on a table (not the same table as the table leg (!) (Not funny-ed.)Equipment:Stopwatch x2Plasticine (2 grams)Weighing scalesMetre stickParachute (plastic carrier bag)Fair Test: I will make sure this is a fair test by using the same size, weight and density plasticine each time. I will do this by weighing it before each experiment. I will use a 5 g ball. In addition, instead of dropping the ball by hand I will try to use another method so that the same amount of plasticine is used each time. A ruler could be used for example so that the plasticine rolls off the edge by itself. After every experiment, I will do a repeat to eliminate any anomalies.Safety precautions: Although there are no immediate dangers with an experiment like this, the working area could be crowded and accidents could happen. To prevent this, I will make sure that my equipment is safely out of the way and packed away at the end of the experiment. Equipment could be moved to the edges of the room and tables could be pushed aside.Modifications to plan:* Ball weight changed to 5.23g (difficult to get an exact measurement)* Drop ball by hand (no feasible way to drop plasticine with a mechanism)* Decision made to not use parachute (would have complicated results)* 20cm is too small to measure as a distance from the ground so this measure was abandoned in favour of 30cm-100cm.* The same person has to drop the same ball or results would not be as accurate.* Plasticine needs to be dropped just above measurement:Preliminary Experiment: To test my procedure and equipment, I carried out preliminary tests and made modifications to my plan (see above). I collected the following results:Height (cm)Time taken (secs)Speed (cm/s)100cm0.7213980cm0.6212960cm0.4513340cm0.3611120cm0.4050To work out the speed of the plasticine I used the following formula triangle:D= DistanceS= SpeedT= Time:. Speed = Distance/ TimeTable of results:Height of drops (cms)Time taken (secs)Repeat of time taken (secs)Average time (secs)Average speed (cm/s)100cm0.550.500.53188.6890cm0.420.400.41219.5180cm0.470.450.46173.9170cm0.370.320.34205.8860cm0.300.380.34176.4750cm0.410.350.38131.5840cm0.320.250.29137.9330cm0.250.200.23130.43Workings:Average time = (Time taken + Repeat time taken)———————————————-2Average speed = Distance————–Average TimeAnalysis: . There is a pattern in my graph but not a very good one because the results were not accurate enough and there were many anomalies. This is because mainly because of human error and problems with the procedure (see evaluation). If the graph made a straighter line, I would conclude that the higher an object is dropped from, the more time it has to accelerate, thus increasing average speed. This would have agreed with my prediction, and in that sense, the experiment was successful.If I had taken more results using a longer distance, I may have seen that as the plasticine fell, its drag would have equalled the weight, and the ball would have fallen at a steady speed; “terminal velocity”. This would have made the graph “level-out”.I also discovered that drag on a falling object depends on the speed of the object and its shape. This is why it was important to re-roll the plasticine to make sure it stayed the same shape.So in more detail; when the plasticine is dropped (with no initial speed) it is moving slowly so the drag is small, the forces are unbalanced so it accelerates. As the ball gets faster, the drag increases until the forces are balanced and it falls at a steady speed (terminal velocity).Evaluation: I have learnt that results of this type of experiment are extremely difficult to take because of the vast margin of error! It is not possible to accurately time such a short drop using a stopwatch, and it would take a much more accurate measuring device to get perfect results. Human error, i.e. reaction time was very important, the stopwatch had to started and stopped at exactly the right time or results would be inaccurate. A way to solve this problem would be to use light-gates or ticker tape to measure the speed. My results on the graph were scattered and not very accurate because of this.My repeats were quite varied from the original set of results. One set of results for the 100cm drop had “0.55 secs” first then “0.50 secs” for the repeat. This means that these results could have been 10% out from the actual time.If I were to repeat the experiment, I would use a more accurate measuring system such as light-gates and a longer distance, for instance 200cm. This would perhaps show terminal velocity and would be easier to time.