Why are there holes in the side of a

washing machine?

Uniform Circular Motion

Round, and round, and

round we go!!!

Purpose

To investigate the relationship between force and velocity of an object moving in a circle with a fixed radius.

Hypothesis

Predict how you think the size of a radius will affect the speed at which an object will move in a circle.

Materials

• string (1.5-2.0m), • rubber stopper, • timer, • straw or pen cylinder, • clip, • 10 large washers, • 1 large paperclip

Procedure

• Assemble your apparatus so the rubber stopper tied to one end of the string will rotate in a circle having a radius of 1 m.

• Begin with 6 washers tied to the other end of the string.

• While rotating the stopper at constant velocity, measure the amount of time required for 20 cycles and record in a data table.

• Repeat this process adding 2 more washers (8 total) and then again for 2 more washers (10 total).

Period (T)

• The period is the amount of time needed to complete one revolution.

• Calculate and record the period for each amount of washers using the time needed to complete 20 revolutions.

Radial Force

• Determine the total mass of the washers.• Convert this mass to kilograms (kg). • Calculate the radial force by determining the

weight of the washers. – The downward weight of the washers is equal to

the radial force exerted on the rubber stopper.

Data Analysis# of

washersTime for

20 rev Period (T) Mass (kg)Radial Force 1/T2

6

8

10

Graph it!

• Plot a graph of Force (F) versus 1/T2. • What kind of relationship do these two

quantities have?• Centripetal force is inversely proportional to

the square of the period (T), does this graph verify this relationship?

Force

1/T2

Radial Force

Check the slope!

• Calculate the slope of the plot. • The slope should equal a value close to

m(4π2R) where m is the mass of the stopper and R is the radius of its path.

• Does this verify the equation F = (m4π2R) / T2

(R.E.R.U.N.) CONCLUSION:

Recall what you did during this lab

Explain why you did this lab and what you were trying to find out

Reflect on the lab’s meaning. If you predicted, did it match your hypothesis? Was your hypothesis wrong? Why?

Uncertainty (errors that were in the lab that you could not control [aka: weather problems, measurement mistakes, etc.] or errors that you came across during the lab that you could fix for the next time you perform this lab)

New questions or new discoveries (normally you put at least three)