Theory
To keep the body moving in a circle, the centripetal force is required. It is provided by the external resultant force towards the centre. To keep the radius unchange, the cantripetal force should alter the angular speed of the object. However, it does no work on the body and the kinetic energy of the body remains unchanged.
By comparing the horizontal and vertical component of the tension, the expression of tthe centripetal force can be deduced. We can find out that the centripetal force=Tsinθ=mω(lsinθ), so T=mlω2. Moreover, ω=, where m=mass of the rubber bung,l=length of the nylon thread, ω=angular speed and t= time taken for complete revolution.
Procedure
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First, weigh and record the mass of the rubber bung(m) in table 1.
- Construct the experimental setup as shown in Figure a.
Figure a
- Then start to whirl the bung. The speed of the bung is then increased until the paper marker on the string is just below the tube about 1cm.
- When the speed become constant, start timing for 30 complete revolutions and record the time in tabe 1. Then repeat the experiment 3 times.
- Repeat the experiment(step1-4) by addind slotted masses to the hanger.
Results and discussion
The rubber bung cannot exactly circle in a horizontal plane because the vertical component has to balance the weight. If the this is exactly horizontal, the vertical component of the tension will be 0N.
The tension T and the weight should be theorectically the same. However, those in table 1 are not the same because of the experimental error. For example, the fan maybe turning on when performing the experiment. There is friction acting on the opening of the glass tube. And the rubber bung cannot be exactly whirled in constant speed and horizomtal plane. Besides, there maybe counting errors of the number of revolutions of the circular orbits made by the rubber bung.
To improve the experiment, we can close the windows and turn off the fan to ensure there almost no wind to influence the result. After eliminating those errors, we can get a result approximately to the theorectical result.
From Figure b, we can also know that the higher the angular speed, the higher the tension. Since the nylon spread is assumed to be on a horizontal plane, so the centripetal force equals to the tension. Hence the higher the angular speed, the higher the centripetal force can be deduced.
Take g=10ms¯²
Table 1
Figure b
Conclusion
From the experiment, we can conclude that the higher the angular speed, the higher the centripetal force. Also, the formula of cenntripetal force=mlω2 can be deduced.
