To help with this investigation, the principle of terminal velocity needs to be applied. As an object falls, it picks up speed. This increase in speed leads to an increase in the amount of air resistance. Eventually the force of air resistance (the upward force) becomes large enough to balance the force of gravity (the downward force). The change in velocity terminates as a result of the balance of forces. At this time the net force is 0 N. Newton’s first law tells us that objects will not accelerate if the net force is 0N.
The more massive the object the higher its speed will be until it encounters terminal velocity. Therefore, more massive objects fall faster than less massive objects because they are acted upon by a larger force of gravity. For this reason they accelerate to higher speeds until the air resistance equals the force of gravity
According to this theory, the heavier the object, the faster the rate of descent.
Method
Equipment: Stop watch- I have chosen this method of timing because it is accurate and easy to use.
Bin bags- they are a very flexible material and move through the air well.
Masses- to change the weight of the parachute,
String- it is light and easy to use.
I intend to test the prediction by timing the fall of parachutes. For the first experiment I will use different surface areas and for the second I will use different masses. I will use a stopwatch to time it so it is accurate and I will drop it from a 2-metre mark on the blackboard. I plan to do six examples for each factor, do each measurement three times and then find the average time. This will ensure a greater accuracy as one can obtain a more accurate average speed by doing many examples. When doing an experiment it is very important to keep all factors except from the one you are investigating the same to ensure the most accurate results.
Preliminary experiment
Aim: To test the methodology and to explore whether the intended parachute sizes gives easily measurable decent times with sufficient variation to detect a trend.
How the surface area affects the rate of descent.
How the mass of the parachutist affects the rate of descent
The preliminary experiment provided some useful results, which will help me to use better measurements in the main experiment. The measurements of area in the first worked well. The material used in the preliminary experiment was too rigid and did not travel smoothly through the air. For my main experiment I have decided to use bin bags which flow through the air more easily. The mass was appropriate for the size of the parachute. All other factors seemed to work well within the experiment. The main experiment will consist of 6 examples rather than three to produce a better range of results. The range of values are very important when doing an experiment i.e. they should not be too big or too small. I feel that range of numbers I have chosen work very well after having done the preliminary experiment and seeing them in action.
Safety
Safety is always an important feature when it comes to executing an experiment even more so when objects are being dropped from a high height. To ensure the highest level of the safety the following issues need to be taken into account;
- No one should be underneath where the object is being dropped
- Care must be taken when standing on chairs
- Running can cause serious accidents.
- Do not leave scissors around as they are sharp and can hurt people
- No rubbish should be left on the floor to prevent people tripping up.
RESULTS
Tables of results
How the surface area affects the rate of descent
How the mass affects the rate of descent
ANALYSIS
Experiment 1
The first experiment looked at how the surface area of a parachute affected its rate of descent. I found out that the larger the surface area, the slower the average rate of descent. The theory behind these results which was discussed in the hypothesis is that when any object falls, it almost always encounters some degree of air resistance. Air resistance is the collisions of air particles with the surface area (facing the floor) whilst falling through the air. The larger the surface area the more collisions there will be. Air resistance slows falling objects downwards as I found out, when doing the experiment. The larger the surface area of the parachute was, the lower the average rate of decent. Below is a diagram, which shows how air resistance affects the fall of an object (a parachute in this case).
Graph
The results that I obtained supported my prediction. I predicted the larger the surface area, the slower the rate of descent and by looking at the graph and table these results are shown. I thought that there would have been a bigger difference between the speeds but the differences between the sizes of parachutes were obviously too small. The bigger the surface area, the more air resistance so therefore it takes a shorter time to reach terminal velocity (the downward and upward force balance each other meaning there is no acceleration). The object does not have to increase to such large speeds as to balance out the forces so it stops accelerating in a shorter amount of time meaning it takes longer to fall. The results produce quite a smooth curve, which did not require a line of best fit. This shows us that the measurements were applied accurately and the experiment was performed efficiently with equitable results.
Experiment 2
This experiment was looking at how the mass of a parachutist and its parachute affects the rate of descent. From my results I found out that the bigger the mass of the parachute, the faster the average rate of descent.
The amount of air resistance depends on the speed of the falling object. Objects will continue to accelerate to higher speeds until they encounter an amount of air resistance, which is equal to their weight. A parachutist with a bigger mass experience a greater force of gravity due to their larger mass (f = 10m) than a parachutist with a smaller mass. A parachute will therefore accelerate to a higher speed before reaching a terminal velocity.
The more massive the object the higher its speed will be until it encounters terminal velocity. Therefore, more massive objects fall faster than less massive objects because they are acted upon by a larger force of gravity. For this reason they accelerate to higher speeds until the air resistance equals the force of gravity
This experiment has demonstrated the theory that the more massive an object, the faster it will fall when encountering air resistance.
My prediction supported the results as each time I increased the mass of the parachute, the faster the average speed was.
Below is a diagram which demonstrates this theory.
Graph
This graph shows the results of the experiment.
This graph did require a line of best fit which shows that the results were not so regular and perhaps were not so accurate. They did show though that the bigger the mass, the faster the rate of descent. The gradient was quite gentle which shows that the speed increased gently.
EVALUATION
The procedure seemed to be accurate and to have gone well and produced some results, which backed up the hypothesis. To try and make the experiment as accurate as possible, I measured the time taken to descend three times and then found an average. To show the calculations for the average speed, I should have written down the different results for the time taken to descend. This would support the figure for the average speed, as it would show that I performed the experiment three times for each different weight or surface area depending on the experiment. I got various different people to time the descent as each person has a different reaction time which in investigations where the measurements are so small it is important that I use different people as a split second can make a big difference. There were no results, which were peculiar or stood out in either experiment. The procedure was suitable for the aim, which I had to complete. I felt that the scientific evidence that I collected at the beginning created a strong basis on which to stand.
My conclusion was firm as I was very sure of the theory behind this investigation after having read up about it and seeing it happen in every day life situations. The evidence which I accumulated was reliable as I had made sure that I could attempt to make everything as accurate as possible. I used a variety of seven measurements, which I felt was enough and as I have seen by the results seemed to work well. As there were no strange results, which seemed out of place I can see that the results were reliable. They were also constant, which backs up, the fact that the results were reliable. Although the experiment went well there are various changes, which I can make to get even more accurate results.
- Use even more measurements, as this will provide more results.
- Do each measurement five times instead of three to get a more accurate measurement.
- Make the structure of the parachute better and not so messy.
- Drop the parachutes from a higher height to get a bigger measurement as this will mean that the reaction time of the person dropping the parachute will make a smaller difference. Use a bigger difference of measurements.
- Take more care to find a material, which flows through the air well.
- Use the stopwatch as accurately as possible.
- Do more examples in the preliminary experiment.
Whilst doing the experiment I tried to do as many things to ensure an accurate result but the problem was time. I felt it was rushed so I did not have as much time as I would have liked. The results did seem to be accurate and were constant which shows that the investigation was not too inaccurate and worked well.
∗ metres per second squared
