# Circular Motion Lab

#### Summary

In this activity students use a circular motion "machine" (made of a stopper, pen casing, string, and weights) to investigate the variables that affect circular motion. The students then graph their data in order to find mathematical relationships between the variables they have studied.

## Learning Goals

The objective of this lesson is to help students understand the relationship between the variables in the equation for circular motion. Students will conduct three experiments. One variable in the circular motion equation will be changed in each experiment. The conclusion of the lab involves deriving the circular motion equation using measured data.

## Context for Use

This lesson is designed for use with conceptual level high school physics students who have already been introduced to differences between centripetal and centrifugal forces and have had practice finding circumference, period, and tangential velocity.

**Subject**: Physics:Classical Mechanics:Rotational Dynamics

**Resource Type**: Activities:Lab Activity

**Grade Level**: High School (9-12)

## Description and Teaching Materials

Lesson Format

- Introduction:

o Class discussion about the variables influencing circular motion

-A force which pulls an object toward the center of a circle is called a ___________ force.

-How much centripetal force needs to be exerted to cause an object to move in a circle?

-The amount of centripetal force that you need to exert depends on:

- 1. the mass of the object you are whirling - heavier objects require more force,

- 2. how fast you are whirling it - going faster requires more force,

- 3. the radius of the circle.

-Lab Background

o Students quick write about the first three lab questions, then share with a partner and revise.

-1. State Newton's first law of motion.

-2. The diagram on the right shows an overhead view of an object moving clockwise in a circular motion. The object is released at point P. Draw the subsequent motion of the body.

-3. What are the two things which must be constant for an object to have a constant velocity?

o Class discussion about the first three questions followed by a demonstration of lab procedure.

o Assign groups and have the class answer questions 4-6 as a group.

o Discuss the answer for questions 4-6 and release students to start the lab.

-Lab work

o Monitor student progress throughout the lab and assist groups that need additional help.

o Assist each group as they apply a best fit line to their graph.

-Conclusion

o Students write the equation for their graph and describe the relationship it shows between variables. Student Handout for Circular Motion lab (Microsoft Word 136kB Aug3 09) Smart Board for Circular Motion Concepts ( 707kB Aug3 09)

- Introduction:

o Class discussion about the variables influencing circular motion

-A force which pulls an object toward the center of a circle is called a ___________ force.

-How much centripetal force needs to be exerted to cause an object to move in a circle?

-The amount of centripetal force that you need to exert depends on:

- 1. the mass of the object you are whirling - heavier objects require more force,

- 2. how fast you are whirling it - going faster requires more force,

- 3. the radius of the circle.

-Lab Background

o Students quick write about the first three lab questions, then share with a partner and revise.

-1. State Newton's first law of motion.

-2. The diagram on the right shows an overhead view of an object moving clockwise in a circular motion. The object is released at point P. Draw the subsequent motion of the body.

-3. What are the two things which must be constant for an object to have a constant velocity?

o Class discussion about the first three questions followed by a demonstration of lab procedure.

o Assign groups and have the class answer questions 4-6 as a group.

o Discuss the answer for questions 4-6 and release students to start the lab.

-Lab work

o Monitor student progress throughout the lab and assist groups that need additional help.

o Assist each group as they apply a best fit line to their graph.

-Conclusion

o Students write the equation for their graph and describe the relationship it shows between variables. Student Handout for Circular Motion lab (Microsoft Word 136kB Aug3 09) Smart Board for Circular Motion Concepts ( 707kB Aug3 09)

## Teaching Notes and Tips

- The students may have trouble at the end of the lab session synthesizing all the equations into one. I have had good luck doing this as a class discussion, depending on student progress.

- Finding the correct fit line for the graphs from lab data will also require some teacher guidance especially if you have not worked with your students on using excel for anything other than linear relationships.

- Finding the correct fit line for the graphs from lab data will also require some teacher guidance especially if you have not worked with your students on using excel for anything other than linear relationships.

## Assessment

Informal assessment of student understanding comes from overseeing their progress in the lab. I also use the SmartBoard file attached as a "pre-test" before the lab and a "post-test" after the lab to gauge student understanding and misconceptions. Further assessment of student understanding of the centripetal force equation is done using practice problem worksheets.

## Standards

Physics 2.2.2.9P Motion of objects for perpendicular forces.