Prediction
I think that the higher the height the longer it will take to hit the ground. The heavier its mass the faster the rate will be. To change the mass, we will be adding paper clips to the paper cake case. How do the forces change as the paper falls?
- At first the only force is the Earth’s pull. This makes the paper accelerate.
- Air resistance increases as the paper moves faster
- When the air resistance is equal in size to the Earth’s pull the forces are balanced.
- The paper falls the rest of the way to the floor at a steady speed, known as terminal velocity.
Preliminary Results
My Results Table
Apparatus
Paper cake cases
2-meter rules
Stop clock
Clamp
Masking tape
This is how my apparatus looked when it was set up
Firstly I set up my apparatus, so that I made it as fair as possible. My first experiment I intended to investigate a height of 10cm. This was quite hard as the human reaction time was not quick enough to get an accurate result. I decided that I would reject this idea. I tried 20cm and this was still hard but it gave me a result that I could work with. I decided that I would concentrate mainly on varying the height. However I will still do an experiment to investigate how the weight of the cake case will affect the rate at which it hits the ground. For my height experiment I am going to do the same thing again and then work out the average, I can then plot this on a graph and comment on any patterns or trends.
I didn’t encounter any major problems when doing my investigation for height. Apart from occasionally the cake case wouldn’t fall straight down to the ground, to solve this we repeated it several times and took the best reading that corresponded with the rest of the results. I thought that this would be a reasonable investigation because it would be quicker than concentrating on mass only. Although I am still going to investigate this it is not my main variable.
Sometimes the ruler would come away from the desk, so we had to make sure it was securely stuck to it with masking tape, we checked this before every test. We also had to make sure that a gap did not appear between the two rulers that were joined and this would give inaccurate results and cause anomalies.
I thought that I would keep my experiment simple so that I could immediately identify any patterns. If I was planning on changing many variables then it would have been more difficult to find the trend.
Method
My method is to investigate the rate at which cake cases hit the ground from varied heights.
To change the height I will get my partner to hold the cake case at the required heights and as she drops it I will measure the time with a stop clock.
I found out that it was easier for me to control the stop clock and measure the heights. Then you are more likely to get accurate results because you are in control of both variables rather than relying on your partner dropping the cake case when you say so.
To make sure my experiment is accurate I will ensure that the height is accurate according the ruler and take more that one reading, using the stop clock. However, it is hard to retrieve the exact time if you repeat it, this is due to human reaction time. The second readings were only a couple of seconds more or less, but this would not affect the experiment so much that a pattern cannot be seen.
I will repeat each experiment 2 or 3 times. Also I will look at other people results to get a rough idea of what figures they are dealing with.
What am going to do to make sure the experiment is safe?
Although we are not dealing with dangerous liquids it is still necessary to wear a lab coat and goggles. Bags should be under the desks so people do not trip over them. To ensure that the equipment is safe, I will make sure that the clamp is securely holding the ruler. I will keep the paper clips in a jar separately so they cannot be misused.
Analysis
After analysing my graph, there is an apparent trend that can be clearly seen. There is a change in my results, as the HEIGHT increases the time is takes to hit the floor increases. My graph is not directly proportional because it does not go through the origin. Also when I look at my results table, if it was directly proportional then as the height doubled so would the time taken, in my case this is not true. There is not a trend to say that is increases quickly in places then in others because it is quite level. My results change steadily.
If I had taken more results then I think that it would have continued going in the same direction, evenly spaced out.
I am going to work out the speed at which the cases are falling.
The speed graph presents a smooth curve. As the height increases, so does the speed. This is true because there is more gravity and air resistance acting on the paper case.
My preliminary results show obvious anomalies; this is why it is good to do a second lot of results. The reason my second set of results were more accurate was because I controlled the stop clock and when the paper case fell. This is true because it was all my reaction times instead of two people’s different ones. I can see that my second results are more accurate by looking at the graph.
My prediction was correct, that as the height increases the longer it takes for the cake case to hit the ground. You can see that this is true by looking at my results table and I have highlighted a part of my graph to indicate this.
The faster you go the more the air resistance. An object dropped is initially hardly moving, so there is hardly any air resistance but as it goes faster there is more air resistance, this means that the downwards force is being made a bit less by the air resistance so it accelerates less (i.e. it will take longer to hit the ground)
I got the results I did because I ensured a fair test at all times. I made sure, that when I stopped the stop clock it was accurate to when the cake case hit the ground, I ensured this by doing it twice and both results were almost the same, this indicates accuracy.
Evaluation
I thought my method was quite reliable, the way I worked in my preliminary work would not have given me accurate enough results, but after addressing why I had so many anomalies, I changed the way I was doing the experiment and it made a big difference to my results.
Problems encountered
- When two people were doing the experiment, trying to get the same results both times was difficult. This affected out results because the readings were widely spaced out and this is incorrect.
How did we overcome this?
We decided to work separately as then it was all our own work and reaction times and this proved to be more accurate
- Sometimes the cake case would not fall straight to the ground as it would hit the ruler and this slowed it down therefore if we had taken that result it would have been inaccurate.
How did I overcome this?
I would make sure the cake case had not got bent in any way as if we had changed the shape of the case accidentally this would affect the way it falls
- Sometimes the ruler would come apart and fall to the ground, As it was only stuck together using masking tape
How did I overcome this?
I would make sure that I had used enough masking tape to securely fit the rulers together and make sure they were attached to the desk properly/
How good were my results?
In my preliminary results I have emboldened the results which have large gaps between them as this indicated poor results.
In my real results the gaps are about 2 seconds different, which isn’t the most accurate but when they are plotted on a graph the same pattern is seen.
Were the results reliable for a good conclusion?
I think my results were reliable enough for a conclusion because it supported my prediction. I took 10 readings, which is the suggested amount to take. If I had taken any more then it would have been interesting to see if the pattern changed in any way. But I don’t think this would have happened because of the forces of gravity and air resistance.
Poor results occurred mainly because of reaction times. However this was fixed, by reducing the number of people conducting the experiment.
Other factors affecting the way the cake case falls
It would have been interesting to see how the results changed if I had decided to use mass as my variable.
I predict that as the cake case gets heavier then the faster it will fall. This is true because the gravity would be more than the air resistance. Also the larger the surface area the slower it will take to hit the ground. This is because the air resistance is pushing upwards in a bigger area.
