We are going to investigate this relationship. We will study how changing F affects the velocity of an object moving in a circle. To do this we will have to keep all of the other variables the same.
- Using the same object for each force value will make sure that the mass of the object remains constant. The object used will be a rubber stopper; it will be attached to the end of a piece of string, which passes through a piece of tubing. The ends of the tubing are polished so that friction is reduced and there is little danger of the string fraying.
- Placing a paper clip just below the grip will ensure the radius stays the same.
The variable I will measure is the velocity of the rubber bung. Using a stop clock the time for 20 revolutions will be recorded. Velocity will then be calculated using
V= 2pi rm
T
Where n is the number of revolutions and T is the time noted. The centripetal force will be altered using 100g masses attached to the end of the string. The lowest mass value will be 100g, it will be increased by adding another 100g mass after each test, the maximum mass value will be 500g.
Apparatus
Plan
- Set up apparatus as shown in the diagram.
- Measure the radius [the distance between the rubber stopper and the top of the rubber tubing].
- Add the correct mass to the end of the piece of string.
- Swing the rubber bung in a horizontal circle at a steady speed, with as little movement of the hand as possible.
- Record how long the rubber stopper takes to do 20 revolutions.
- The number of masses is then increased and the experiment is repeated.
- Repeat the whole experiment three times.
- Calculate the average velocity squared value for each force.
- Plot graph.
Prediction
I believe that when I increase the force acting on the string, the velocity will increase. This is because the force increases the centripetal force; the following equations will prove this. By keeping the radius and force the same, the velocity can be shown using equations.
Force = mass * velocity
Radius
1 = 1v squared 1 = 1v squared = vsquared
radius 1 1
If I double the mass [the force will double], I think V will also double.
For force = 2
2= 1v squared = 2 = 1v squared = 2 v squared
r 1 1
Obtaining
Results table
[Force = mass * gravity, which is 10 N]
Analysis
There is a definite pattern in the results, which is a gradual decrease in time. We have created a graph to prove the pattern. The graph shows a positive correlation, and the plots fit into a line of best fit. There is a simple pattern between the plots, they gradually increase and are almost equally spaced out. However there is an anomalous result.
My prediction was correct, my statement was that if I increase the force acting on string-velocity would increase. This rule is true, as force = mass times velocity divided by radius. If we where to increase mass, force would increase. We kept the radius and force the same, as these would affect the results. I have done calculations in my prediction to prove this theory.
Evaluation
Personally I believe the investigation was well, as we carried it out as planned. The results where good, they where what I expected. However, I did receive one anomaly. It should have slightly lower in time. The anomalous result was slightly lower than expected. The cause of the anomaly could have been many things, from applying too much pressure to a change in the radius. [By accident] I could improve my method to not get any anomalies by the following:
- Have a stronger radius attached [between the string and rubber]
- Measuring beforehand the preasure
- Using a stronger string
- Use glass tubing polished instead of rubber [to reduce friction]
I could extend this investigation by testing the centripetal force in different ways, like at an angle, or at various equilibrium. Or altering the mass of the rubber bung. Altering the mass would be the most suitable way of extending this investigation, we could see what happens if there is a larger centripetal force. [By increasing mass, see if there is still a pattern between even mass changes-e.g. 700 , 800 etc.]
