Prediction
I predict that as I increase the surface area of the canopy the time at which the weight takes to fall the distance of 4.5 metres (4500 millimetres) will steadily increase therefore the speed will decrease. Based on my preliminary results by using a suitable a range of canopy sizes I will be able to prove this statement.
Hypothesis
Terminal velocity is when an object has equal forces acting on it as it falls. When the parachute falls the two forces acting on it are air resistance (pushing upwards) and the weight of the object (pushing downwards). An object can only reach its terminal velocity when the forces of air resistance and weight are balanced. Because I am changing the surface area of the canopy the larger the canopy the more resistance there will be.
Changes based on prelininary results
In the prelininary experiment I used parachutes with the following measurements:-
- 25cm by 25cm
- 35cm by 35cm
- 45cm by 45cm
These three were going to be the largest of my parachutes (the other 2 were measured as 5cm by 5cm and 15cm by 15cm). By looking at the parachutes perfomance in my preliminary experiment I noticed that parachute 1 was barely creating enough drag for the object to reach its terminal velocity. By looking at my results below you can see that the results for the 25cm by 25cm parachute was over a larger range, this implies that it is unreliable.
I realised that if a parachute of 25cm by 25cm wasn’t creating enough drag then my 2 smaller parachutes wouldn’t stand a chance, they would be very unreliable and I wouldn’t get suitable results from them. I decided to use 2 larger canopies 55cm by 55cm and 65cm by 65cm.
Equipment
For this investigation I will need the following list of equipment:-
- Scissors
-
Plastic Bag (large enough to make 5 parachutes with measurments of 25cm2, 35 cm2, 45 cm2, 55 cm2 and 65 cm2)
- Plastecine (aproximatley 30.0 grams)
- Scales (to weigh the plastecine)
- Metre rule
- String
- Stop clock
- Compass (to pearce the canopy and place the string)
- Pencil,Pen and Paper etc
Method
Prepare and make 5 parachutes with measurements 25cm by 25cm, 35cm by 35cm, 45cm by 45cm, 55cm by 55cm and 65cm by 65cm:-
- Use the plastic bag, scissors, metre rule and pen
- Cut 20 pieces of string and attach them to the canopy
- Prepare the plastecine and weigh it on the top pan balance (record the weight0
- Attatch the plastecine to the parachute – its ready for flight.
Find a suitable space with plenty of height to drop the parachute from (a stair well would be adequate) measure the height and ensure that it is reasonable enough for the parachute and object to be able to reach its terminal velocity.Drop the parachute from the same place each time to make sure the investigation is fair.
Drop each parachute and time it with the stop watch until it falls to the ground, record the time and repeat 5 times. Record all results in a suitable table and calculate an average for each set.
To guarantee that the experiment is fair do the following:-
- Make sure the plastecine weighs the same (weight will encourage a different effect on the parachute, if it is heavier it the time at which it will reach its terminal velocity will decrease, if it’s lighter the time at which the terminal velocity is reached will increase).
- Drop the parachute from the same point, same distance (a longer distance will take a longer time to fall and vicer versa).
- The length of the parachutes strings will be kept constant (if the
- There will be a clear passage for the parachute to fall (any interfearance will cause the experiment to be classed as void and repeated).
- Windows and doors will be kept closed (to prevent a draft from swaying the course of the parachute).
Results
After getting my results I calculated the speed at which the parachute was falling each time. I used the average speed and the following formular:-
Speed = Distance ÷ Time
Anaylisis
My results clearly show how the suface area of the canopy of the parachute affects the speed at which the object falls. I can see that as the surface area increases the speed at which the parachute falls decreases and the time it takes to fall increases. This is because the larger the surface area of the canopy the more air resistance it provides.
Air resistance is friction between the air and the canopy, another way of saying this is theamount of air caught by the canopy. Obviously with a larger canopy you will catch more air whilst falling and so with a larger canopy the time the parachute takes to fall will increase and the spead will decrease.
When there is a large amount air resistance the weight is balanced quicker therefore the object reached its terminal velocity quicker and will fall at a steady speed to the ground. There is a difference of 1.59 seconds between a parachute with a surface area of 25cm2 and a one of 65 cm2 takes to fall the distance of 4.5 metres. The parachute with the larger canopy must have reached its terminal velocity faster and so fell at a steady speed.
The graph on the following page shows the relationship between surface area and terminal velocity. As you can see the line increases steadily showing that as the surface area increases so does the time it takes to fall. We could say that as the canopy size increases the level of air resistance also increases and so the time taken for the parachute to fall will alos increase.
The next graph shows the relationship between surface area and speed. I can see that the line steadily falls. I could say that as th surface area of the canopy increases the amount of friction between the canopy and the air also increases and so the speed falls.
I was correct in my prediction as the time taken for a parachute to fall increases with the increase in surface area of the canopy and the speed that the parachute falls at decreases with the increase in surface area of the canopy.
Evaluation
I think I would be right to say my results were acurate enough to be relaible and support my findings, but of course there is far more tecnologically advanced equipment that can be used to give my results a higher degree of accuracy for example instead of using stop clocks I could use an electronic light gate, because of reactions times time is added on even if it is only minor the average time can be much higher than it should be.
On my first graph I experienced 1 anomalous result; the parachute with a surface area of 45cm2 took 2.56 seconds to fall according to the line graph it should have taken 2.42 seconds. On the second graph there was also an anomalie, it was for the same parachute the speed at which the parachute fell was 1.76m/s where as it should have been 1.86m/s. The anomalie was from the same parachute because the graphs are dependant on each other, the second graph depends on numbers used on the first i.e average time.
Possible reasons for the anomalies are as follows:-
- Weight change (Pieces of plastecine could have fallen off during flight, the top pan balance may not be acurate enough – because the parachute is lighter it would take longer to fall, falling at a slower speed)
- The distance may have been altered slightly (if the distance was extended then it would take longer to fall, therefore the time recorded could have been extended)
- The parachute strings could have been altered (when attaching, the string length could have been shorter making the object more bulky and creating more air resistance)
- Minor interfearances I.e bumping into things but not stopping (to the spectator a minor interfearnce could seem as nothing because the object does not stop but colliding causes the parachute to fall at a slower rate taking more time)
- Slight drafts could have caused the parachute to sway off course (diagram above)
The list above causes me to realize factors that could have affected my results and so I must take into account this and how it could affect my conclusion.
My results were over a suitable range, if I was to extend this particular experiment I would add extra parachutes such as 75cm2, 85cm2 and 95cm2 to see whether the pattern continues.
Now that I have investigated how the surface area of the canopy affects the rate at which the parachute falls I could look into the weight of the object to see how this affects the speed at which the parachute falls. I would have to take into consideration a suitable size canopy to make sure that the parachute will be able to reach its terminal velocity.
I could look into the length of the parachute strings to see what affect this has on the speed at which the parachute falls. I could look at the height at which the parachute is dropped, obviously if it is higher it will take longer to fall but would the parachute travel at its terminal velocity for a longer period of time?
The material of the canopy can make a difference also; different materials have a different weight, some materials are more streamlined than others. Parachutes with a less streamlined canopy would have more air resistance; this would cause the parachute to fall slower therefore affecting the rate at which the parachute falls.