Objective : To measure the centripetal force by whirling it around a horizontal circle, then compare the result with theoretical value FC = m(2r. Apparatus : 1Rubber bung 1Glass tube (About 15 cm long) 1Slotted weights, with hanger 12 ? 0. 02 kg 1Nylon thread 1. 5 m 1Paper marker 1Adhesive tape 1Metre rule 1Stop watch 1Safety goggles Set-up: Procedure: 1. Attach one end of a 1. 5 m length of nylon thread to a rubber bung and thread the other end through a glass tube, a paper marker and a number of weights as shown. . First adjust the position of the marker so that it is about 1 cm near one end of the glass tube, and the length of the thread L from the other end of the glass tube to the rubber bung is, say, 0. 8 m. Fix the position of the marker using adhesive tape if necessary. First start with M = 0. 16 kg (i. e. 160 g). 3. Holding the glass tube vertically, whirl the bung around above your head in a horizontal circle. Increase the speed of the bung gradually and allow it to move out (i. e. et L increases) until the marker is about 1 cm below the lower end of the glass tube. 4. Try to keep the angular speed constant so that the marker is always about 1 cm below the tube throughout. Ask your partner to time 20 revolutions of the bung using a stop watch. Remember to start the stop watch at 0 and stop it at 20. Take one more confirmatory reading and obtain the mean time for 20 revolutions. 5. The ? horizontal? component of the tension T of the string provides the centripetal acceleration of the rubber bung. Theory:

As there is no vertical motion, the vertical component of tension(T ) is balanced by the weight of the bung: Tcos[pic]=mg_____ (1) The horizontal component of the tension provides the net centripetal force: Tsin[pic]=mr(2_____ (2) Substituting r= l [email protected] into equation (2), we can find the tension(T ) in the string. Tsin[pic]=m(L sin[pic])(2 T=mL(2 The tension (T ) is provided by the weight(Mg). By comparing the two values of tension, the expression of centripetal force F =mr(2 can be verified. Precaution & Safety Measures ? Wear the safety goggles during experiment The angular speed of the motion should be kept constant so that the marker was always about 1 cm below the tube. ? Have all observations by standing away as the demonstrator rotates the rubber bung ? Make sure that you have plenty of room and you may rotate horizontal circular path. Also, switch off the fans. ? Ensure the rubber bung hold tightly with the string. ? Ensure the paper marker at the same position during experiment. ? Count the numbers of turns begin at 0. Data: (I)Readings Measure the mass m of the rubber bung. m = 0. 0316kg Length of the string= 0. m |M / kg |Mg / N |Time for 20 revolutions 20T / s |Angular speed |m(2L / N | | | | |(=[pic] / rad s-1 | | | | |1st trial |2nd trial |Mean | | | |0. 12 |1. 18 |16. 03 |16. 47 |16. 25 |7. 73 |1. 511 | |0. 16 |1. 7 |15. 22 |15. 41 |15. 32 |8. 20 |1. 700 | |0. 20 |1. 96 |14. 54 |15. 13 |14. 84 |8. 46 |1. 809 | |0. 24 |2. 35 |13. 50 |13. 56 |13. 53 |9. 29 |2. 182 | Mean m[pic]L: [pic] Data Analysis: I) Equation Tsin[pic]=mL(2 II) Calculations(% of Error) For 0. 12kg, For 0. 16kg [pic] [pic]

For 0. 20kg For 0. 24kg [pic] [pic] III) Graph [pic] Source of error: ? Air resistance exists. ? Friction between the glass tube and the string ? Friction exists when the paper marker contact with the glass tube ? Length of string, L may change during experiment ? Centripetal force is T sin[pic],however, the angle[pic] may not uniform . (T is always Mg) ? Rubber bung may not whirl into horizontal circular path. ? Rubber bung can not whirl with angular speed. ? Reaction time of students exists (Human error). Paper Marker may move along the string and affect the length of L. Improvement: ? Conduct the experiment indoor ? Use a better string and glass with less friction ? Obtain the mean time for 20 revolutions and less than 50 revolutions ? Fix the position of the paper marker dually with pen Conclusion: On account of the errors, the centripetal force which measured in the experiment is greater than the theoretical value. ———————– M paper marker rubber bung of mass m glass tube 1. 5 m length of nylon thread glass tube paper marker slotted weights M rubber bung



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