Centripetal force
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Introduction
Student Name: WONG Wing Yan
Class and class no. : 6G2 (22)
Date of experiment: 11th March, 2009
Experiment 2  Centripetal force
Objective
In this experiment, we are going the centripetal force for whirling a mass around a horizontal circle; then we compare experimental result with the theoretical value given by the formula.
Apparatus








Setup
Theory
When a mass m attached to a string id whirled around a horizontal circle with radius r, according to the Newton’s First Law of Motion, there must be a force acting on it. It is a centripetal force for maintaining the circular motion. To produce centripetal acceleration, a centripetal force is needed. The centripetal force is given by
where is the angular velocity of the circular motion. The force is provided by the tension of the string and it must be directed towards the centre of the circular path.
We can substitute into the formula for F,
Middle
28
32
35
44
Data analysis and Results
Tabulate the results as follows:
Mass of rubber bung m = 0.01369g
Mass of slotted weight M: 0.05kg
Tension in string T = Mg = 0.05x9.8N = 0.49N
Length of string /m  0.25  0.4  0.5  0.7 
Time for 50 revolutions 50 t/s  28  32  35  44 
/rad  11.22  9.82  8.98  7.14 
0.4309  0.5281  0.5520  0.4885 
Mean = (0.4309+0.5281+0.5520+0.4885) =0.4999 N
Standard deviation = 0.0458
Discussion
The percentage error between the theoretical value of the tension 𝑇 and the experimental value is：
The experimental value is larger than theoretical value tension 𝑇, since there is some source of error in this experiment.
Firstly, the position of the paper clip may not be the same, since the label indicate the length of the string, L fluctuates during the experiment, the length of the string beyond the upper opening is not constant. From the formula :
when the value of L is increased, the experimental result will be larger than the theoretical result. Oppositely, when the value of is decreased, the experimental result will be smaller than the theoretical result. Therefore, the results are affected by different value of .
Conclusion
For the horizontal circular motion:
From the equation,
We can know that when the angular velocity increases, will also increase.
Conclusion
In this experiment, we try to measure the centripetal force by whirling a mass in a horizontal circle for circular motion. We show that regardless of the angle.
We compare the experimental value to theoretical value and find that the experimental one is a bit larger than the theoretical value, which is due to the error of this experiment.
It is also clear to show that is a constant. And from the formula, r, we can know the relationship between m and r, which is .
We can improve the experiment by moving the rubber bung in a constant speed. Also, the rubber bung should be set in a horizontal circular path. We should also keep the length of the string beyond the upper opening constant. The time for more revolutions of the circular motion could be taken for a more precise result.
Reference
 New Way Physics for Advance Level – Book1(Mechanics) ; Manhattan Press (H.K.) LTD, page 172173
 http://en.wikipedia.org/wiki/Centripetal_force
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