Year 10 Air resistance experiment 1

I got a plastic sandwich bag from the kitchen and taped a piece of string to it. I made a loop in the string so I could hang paperclips from it.

Then I held it up as high as I could, making sure the bag was open as much as possible to catch the air. I timed how long it took to fall to the floor.

I started with no paper clips on the string at all. When an object is falling in the air, the weight (gravitational attraction) is pulling it downwards as its driving force. The air resistance acts as a counter force to try to stop this happening. Air resistance depends on both area and speed. As the bag falls, the weight makes it go faster. This increases the air resistance. When the air resistance becomes as big as the weight, the speed stops increasing. It carries on down at steady speed which is called the TERMINAL VELOCITY. When I started adding paperclips the weight got bigger so it had to fall further and was able to go faster before it reached terminal velocity. So adding more paperclips makes the time for the fall decrease as shown on the graph of my results below. Notice that it is levelling off. If there was no air in the room, it would have taken 0.66 seconds to hit the ground.

 The results table for the experiment is below.

The number of paperclips was the independent variable because it was the thing I deliberately chose to change. It is the independent variable because I can write in the numbers on the table before I even start.
The time is the dependent variable because these are numbers that I can only find out by doing the experiment.
I kept the height of fall the same throughout the experiment so that was a CONTROL VARIABLE.