Factors affecting the terminal velocity of a falling cone

When a cone is dropped from a certain height, a force known as air resistance is acting on it to try and slow down its rate of descent. When an object is first dropped the only force acting on it is its own weight pulling it down. Because no force is acting against it, it accelerates. As it accelerates air resistance begins to act upon it but the forces are still unbalanced so the cone still accelerates. As the two forces, weight and air resistance, balance the object reaches terminal velocity and is at a constant speed and not accelerating. This is what will happen to the cone as it is dropped in this experiment.

Factors that could I could change

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To affect the terminal velocity of my falling cone I could change many factors:

* The weight of the cone- adding pieces of plastercine

* Air resistance- reducing the surface area of the cone

* Speed-start the timer as soon as we drop it

We have chosen to change the Air resistance on the cone by reducing the surface are. We will do this by making 1cm in diameter holes in the cone by using a hole punch.

Variables

The variables that I will have in my experiment are:

* Measuring- time

* Changing- Air resistance (surface area of cone) that I will be changing with a hole punch.

I will keep constant:

* Height – dropping from ceiling, 3 metres

– measuring from 2 metres

* Same place in room

* Same day- same conditions

* Same person dropping the cone

* The holes are the same size

* The same cone

Prediction

I predict that as more holes get added into the cone the quicker it will fall. This is because adding holes reduces the surface area of the cone which reduces the air resistance. Therefore the cone will accelerate for longer before it reaches terminal velocity, therefore reaching higher speed at terminal velocity, which will mean it goes faster.

Apparatus

* Metre ruler- to measure one meter from the ceiling

* Stop clock- to measure the time taken for the cone to reach the floor

* Hole punch- to make the holes in the cone

* Paper- to make the cone

* Glue- to glue the cone together

Method

In our experiment we will drop cones from the ceiling which is 3 metres high, we will let it accelerate for 1 metre then time how long it takes for it to fall the remaining two metres. We will drop the cone three times then record the average. The first time we drop it, it will have no holes in but we will add one extra hole after we have taken the average of the times of the last 3 drops and see what difference it will make. The holes will be 1cm in diameter and will be made with a hole punch, and the cone will be 20.5 cm in diameter and will be made out of paper.

No. of holes

1 (seconds)

2 (seconds)

3 (seconds)

Average (seconds)

Speed

(m/s)

0

1.17

1.23

1.11

1.17

1.70

1

0.99

1.02

1.02

1.01

1.98

2

1.05

0.92

0.97

0.98

2.04

3

0.93

0.97

0.95

0.95

2.11

4

0.91

0.93

0.98

0.94

2.12

5

0.80

0.74

0.77

0.77

2.59

6

0.71

0.76

0.75

0.74

2.70

7

0.79

0.76

0.73

0.76

2.63

8

0.68

0.65

0.74

0.69

2.89

9

0.63

0.67

0.74

0.68

2.94

10

0.61

0.68

0.69

0.66

3.03

Conclusion

My results support the prediction that as the number of holes increased the speed of the cone would also increase, due to reduced air resistance. This is because as every hole was added the air resistance became lower, therefore it took longer to balance out the two forces acting on the cone. The force of weight acting down on the cone was greater than the air resistance acting upwards, therefore the cone accelerated. As the air resistance the cone accelerated for a longer period of time, as it took longer to balance out the uneven forces. Therefore as the number of holes increased, the cone accelerated for longer before reaching terminal velocity. For example, a cone without one hole would accelerate for a shorter period of time before reaching terminal velocity than a cone with 7 holes. The cone with 7 holes

would accelerate for longer and then reach a faster constant speed, which would also increase the overall speed at which it fell.

Evaluation

There are many positive procedures during this experiment, dropping the cone 3 meters and measuring it 2 metres allowed the cone to reach terminal velocity.

When adding holes to the cone the same hole punch was used ensuring that all the holes were the same size.

One person dropped the cone and another person timed it, these stayed the same therefore reducing the variables. Each drop was then repeated three times and an average was taken, this increased reliability. However when the holes were punched they were unevenly spread out which affected the way the cone fell. If I did it again I would spread the holes out evenly.

The results from my experiment are reliable and sufficient. I know this as there is just the one odd result, this occurred when the cone had 7 holes in it. This could have been for two reasons, there could have been a door or a window opened somewhere in the room or the person timing could have lost concentration. Despite this my results were sufficient enough to support my prediction. There is also constant pattern in that as the number of holes increased so did the speed that it fell which meant a strong positive correlation on my graph.

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