Prediction:
I predict that the ping-pong ball will not bounce as high up as it was when originally dropped. I predict so because I do not think the ping-pong ball bouncing on a laboratory floor is very efficient (50% - 80%). Lots of energy is lost as heat or sound. Since a ping-pong ball is being used, when dropped from higher distances more energy is lost due to the force of air resistance. Considering this factor I predict that the ping-pong ball will bounce more efficiently as it is dropped closer to the ground.
I also can predict the shape of the graph. The height of the bounce will go along the Y-axis, and the height from which the ball was dropped would go along the X-axis. There will be a curve, and positive correlation. The curve will be more and more towards the X aces. This is a sketch of how I predict the graph will look:
( GRAPH OF PREDICTION – TRUSEN I couldn’t giv u diagrams btw)
I predicted the curve because I took air resistance into account. As the ball is dropped from higher up, it will have a longer time to speed up and so will face more air resistance. The ball loses energy when faced with air resistance, mainly as heat. Since this energy is lost, the ball will bounce less efficiently.
Theory:
In this experiment there are many variables. Measuring any one variable and keeping the rest constant can solve the aim of the experiment. The variables are;
- Height of drop
- Surface that the ball will have contact with
- Temperature of surroundings
- Air resistance
- Quality of ball
- Size of ball
- Weight of ball
Out of all these variables I chose to vary the height of the drop, because this was the easiest factor to vary.
As the ball is dropped higher from the ground the ball will become less efficient as it loses more energy to air resistance. Yet eventually the ball will reach its terminal velocity. The ball will also lose more heat on impact with the surface when dropped further away from the ground. Wit this information we would expect a graph with slight curve downwards towards the axis of drop height, as we get closer to 0mm away from the ground.
Results:
(TABLE)
Preliminary Experiment:
I conducted a preliminary experiment in order to get a rough idea of when air resistance has considerable affects on the ping-pong ball. In my preliminary experiment I got a ping-pong ball and a golf ball, I then dropped them together, from different heights until I could hear two different bounces, i.e. the balls hit the ground at different times. The heavier golf ball would be less susceptible to air resistance than the lighter, less dense ping-pong ball. I needed reasonably accurate results to help me with my proper experiment. To do so I conducted the preliminary experiment on the same day as I conducted my main experiment. The room was therefore at the same temperature. I also used the same ball and surface for both experiments. In my preliminary experiment when I heard two different bounces, I repeated dropping the balls at the same time at that particular height. I did not hear two different bounces until I started dropping the balls at around 2 metres from the ground. So I decided that I would begin to drop balls from 2 metres in my proper experiment to see the affect of air resistance and the efficiency of the ball. 2 metres was also quite convenient as I could place two 1metre rulers vertically to measure the drop height.
So using my results I tested air resistance by starting to drop the ball from two metres above the ground. Here is a table that shows my results:
(TABLE …)
Andrew Dhushantha
Physics Analysis
Analysis:
We have found out from the evidence that when a ball is dropped from a height it loses energy on its way to the ground and when it hits the ground. The amount of energy lost during this determines how high the ball will bounce, and the efficiency of the ball.
As the graph shows, the efficiency of the ball decreases as it is dropped further away from the ground. We can see that air resistance does not affect the bounce of the ball much until the ball is dropped from as high as about 140 cm. I chose to draw a freehand curve for the graph because the curve reflects better the affect of air resistance. A straight line would have failed to do this. The graph starts to curve more considerably as air resistance is taking place more. The ball loses energy due to air resistance as it is transferred to heat; therefore the ball bounces less efficiently.
Air resistance increases with drop height as the ball has more time to accelerate, and so when acceleration takes place in the air, the ball heats up, losing energy. The ball loses even more energy when it hits the ground. The surface it interacts with absorbs some energy; some energy is lost as sound or heat. It is due to the contact between the surface's interactions with the ball that 40% of the energy is lost during each bounce; this is proven by my graph. As when the ball is dropped from 10 cm, where air resistance is minimal, the ball bounces up 6 cm. we can calculate the efficiency of the ball like this:
6/10 = 0.6
0.6 X 100 = 60%
Therefore the ball is 60% efficient.
My prediction was very accurate. The sketch of the graph I predicted turned out as I expected. Both the graph and the sketch have the same general shape. My prediction that the ping-pong ball on a laboratory floor would not be very efficient was correct. The ping-pong ball is 60% efficient when dropped from my lowest reading (10cm) and 53% efficient when dropped from my highest measurement (2 metres). This is due to the build up of air resistance acting upon the ball as the drop height increases. Therefore my prediction that the ping-pong ball would be between 50%-80% efficient was correct. Yet the 80% was too excessive as even if I conducted the experiment on a far larger scale the most efficient the ball could get in the experiment is around 60% or 65%. This is because the ball was 60% efficient when it was dropped from 10 cm so there is only a very small amount of air resistance acting on the ball here. The efficiency can not increase much from this point as seen on the graph.
Andrew Dhushantha
Evaluating Evidence
Evaluation:
I am quite satisfied with my results as they fitted my prediction very well. They showed all the expected trends for the bounce of a ping-pong ball. My results showed the affect of air resistance on the ball's efficiency very well as well. It even showed that efficiency reduces with a higher drop height.
The results are very reliable as I recorded many points for the experiment, repeated the entire set 2 more times and took an average. During the experiment, I obtained some anomalous results. Most anomalous results were a result of me not taking into account the error of parallax when measuring the bounce height. If I had kept at eye level when measuring the bottom of the ball I would not have got the anomalous results I had. Some of the readings were also inaccurate because when reading the bounce height, the ruler was slanted, and not straight vertically. This led to the ball seeming to have bounced higher than it should have. I made sure that I rectified any anomalous results by repeating them. I considered the results anomalous if they were at least 2mm away from the best-fit curve. This helped me get very accurate results. The fact that I made sure I conducted a fair test also makes the results even more reliable. I repeated each result at least 3 times before taking the average result.
Anomalous results stem from a change of any of the variables other than those, which are required to be altered during the experiment. An example of this is a change of temperature. This is why I conducted the entire experiment within 40 minutes to ensure that the variable of temperature did not alter too much. Anomalous results could also have occurred if when recording the height of the ball, our eyes were not at the same level as the bottom of the ball.
To improve the experiment, we should be able to control all of the variables, which are listed below:
- Height of drop
- Surface that the ball will have contact with
- Temperature of surroundings
- Air resistance
- Quality of ball
- Size of ball
- Weight of ball
The only variable out of these that should not remain constant would be the height of the drop of the ping-pong ball. So to control temperature, the room in which the experiment is conducted in should have its temperature controlled and maintained at around 25 degrees Celsius.
When recording the height of the ball, results could have been more accurate. For example, a video camera could be used so that it could be played at slow motion and the very accurate result could be recorded. Wider rulers could be used so that even if the ball is dropped to the side, the proper measurement can clearly be seen.
Some further work could be conducted for this experiment. The ball can be tested to see if it can reach terminal velocity. This would mean dropping the ping-pong ball from very high places, for example, the top of a building. A ruler can be painted vertically up the building so that when the ball bounces, a camera can be used to record the bounce of the ball. This recording can then be slowed down so that a more accurate reading can be obtained. This might not be very practical though because the wind may blow the ball away, so the experiment could be conducted in a very calm day.
When the ball bounces up, does air resistance still affect it? This could be found out by seeing how efficient a ball is when dropping from 1 metre. Then its efficiency can be measured when it bounces up to 1 metre and then drops and bounces back up. This will tell us if the ball loses energy when bouncing upwards.