To investigate how the weight of an object affects its terminal velocity as it is falling

Aim

To investigate how the weight of an object affects its terminal velocity as it is falling.

Prediction

I predict that when the weight of a falling object is increased the terminal velocity will also increase.

I think this because as you increase an objects weight it has a larger downwards force. In order for the object to travel at a constant speed, i.e. terminal velocity, another force must match the downward force. This force is air resistance. So to make air resistance the same size as the downward force, the object has to be travelling at a fast enough velocity. A heavier weight will accelerate to a higher terminal velocity before these two forces are balanced than a lighter one. This is because air resistance increases when velocity increases as more air particles collide with the object, which slows the acceleration of the object down. So the heavier the object the larger the downward force so more air resistance is needed to balance the two forces so a higher velocity is needed.

If the weight of the object is doubled I predict that the terminal velocity will also be doubled. I think this because when the weight of an object is doubled it has a twice as large downward force. So in order to balance this doubled force air resistance has to produce the size force as it, (this is when the object reaches its terminal velocity). In order for this to do this, the object must double its speed so air resistance doubles and so matching the downward force.

Falling Masses

Method

In this experiment we are going to drop a paper cone with different sized weights in it from a height. Using a stopwatch we will time how long it takes for the cone to reach the floor. A stopwatch is used because it is very precise to the nearest 1000th of a second whereas a clock only times to the nearest second. The faster the object is falling the less time it will take to reach the floor.

Apparatus

For this experiment we will need:

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Falling Masses

Method

Apparatus

For this experiment we will need:

A4 sheet of paper
Compass
Scissors
Plasticine
Metre ruler
Stopwatch
Glue
Scales

Preliminary Work

The aim is to find a suitable size for the paper cone and a good weight of plasticine to use.

We did this by experimenting with different sized cones and masses. If the cone were too small it would drop too quickly making the time on the stopwatch inaccurate. This is because of the human reaction time, which is about 0.2 seconds. It would have a large effect on the short times that the cone took to reach the floor. If the cone were too big it ‘flutters’ down making the falling time very inaccurate. We found that a suitable size for the cone was one with a diameter of 20 cm. Also the cone shape had to be considered as to whether it was to be a shallow or deep cone. If the cone was to shallow the cone would fall much to slowly and it would ‘flutter’ down and if the cone were too deep it would fall too quickly making the times inaccurate.

If the weight were too large, the cone would drop too quickly for the timer and if it were too light it would not make much difference between the falling times. We found that using one-gram masses were suitable.

For this experiment a 20 cm (diameter) cone and one-gram masses will be used. I think the cone should be dropped from a height of 2.00 metres, as this is a good distance to time without a large effect from reaction times.

Cone Making

A circle is drawn (using a compass) with a diameter of 20 cm and then cut out. A straight line is drawn from the centre of the circle to the edge and then cut along. Section A is put over section B and stuck down to make a cone shape. If sections A and B are small the cone will be quite shallow so there will be more air resistance making it easy to time its falling time.

Method

To do this experiment, make a cone as instructed above and prepare 5 pieces of plasticine using the scales to make them roughly 1 gram each. Measure and record the weights of each piece using a set of scales precise to a hundredth of a gram. This means that the results will be accurate.

Measure 2.00m on the wall with a metre ruler, which is the height the cone will be dropped from.

Put the first of the plasticine masses in the cone. The exact weight is needed for accurate results. Hold the cone so that the tip is on the 2.00m mark. Let it drop. The stopwatch should be started at this point and then stopped when the tip of the cone hits the floor. Record the time given by the stopwatch.

Repeat this five times but put another of the plasticine pieces in each time so you have five pieces of plasticine in the cone on the fifth drop. Remember to weigh and record the weights of all the plasticine in the cone.

Diagram

Fair Test

In order to make this experiment a fair test it must be precise and reliable.

Only the plasticine weights should be changed. Each time the weight is increased it should be weighed to get accurate results.

The cone has to be dropped from exactly the same height (tip of cone at the 2.00m point) every time to make a fair test. Also, make sure the cone does not come into contact with anything while it is falling, as this will alter the results.

So that this experiment is reliable it should be repeated at least twice. This is because times may be different, caused by reaction times. An average time can be made for each weight. The more repeats that are made the more reliable this experiment is going to be. When repeating, the weights have to stay exactly the same as the first time so not to make the results inaccurate.

Results