# Physics equations/06-Uniform Circular Motion and Gravitation/A:device

Date:   /       /       Course: Phy2400     Last, First name: ___________________________ __________

## Lab on uniform circular motion

• Each student should do his or her own write-up to be handed in at the end of today's lab period. If an investigation requires more than one lab period, you will hand in a separate writeup for each lab.
• The labs will be graded on a Satisfactory/Unsatisfactory basis. Unsatisfactory labs will be returned, but may be resubmitted with no penalty.
• Labs are more fun if you have control over procedures. You may take liberties with your investigation, provided it is focused on this topic, and provided it is not an attempt to study material for this or any other course. If any member of your group violates this, please intervene.
1. Work in groups to derive the formula for uniform circular motion: a=v2/r. Carefully define each term.
2. Make a hand-drawn sketch of the centripetal force device, in both 'static' and 'rotating mode'. In static mode, the spring is opposed by a 'hanging weight'. It is very important that in both 'static' and 'rotating mode', the 'support rod' and string be at exactly 90 degrees. Place the 'positioning rod' just below the lower tip of the rotating mass. Label the following items:
rotating mass  hanging mass   support rod   counter weight   orbital radius   spring
3. In 'static mode', measure the following parameters, and record their values in SI units. Include an uncertainty for each measurement.:
rotating mass  hanging mass   radius of orbit   counter weight   orbital radius   spring
4. In 'rotating mode', measure the period of orbit, T. Perform this measurement using at least two different procedures, and for each procedure make at least three measurements. For example a minimal effort might involve:
1. Time to make one revolution, measured three times.
2. Time to make 10 revolutions, measured three times.
5. From our data, select a value of period, T, and use that to calculate the speed of the mass.
6. Use the measured radius of orbit and speed to calculate the centripetal acceleration, a=v2/r.
7. Use the measured rotating mass to deduce the centripetal force, FC=mrota
8. Use the concept of weight and the value of the hanging mass to calculate the tension in the spring, FS=mhangg
9. Calculate the % difference between FC and FS using two procedures:
1. (Big-Small)/Average
2. Big/Small - 1