**Pendulums**

John J. Miller Maine East High School

6801 W. Dempster

Park Ridge IL 60048

(708)825-4484

**Objectives**:

The students will be able to determine what factors effect the period (time

to swing back and forth) of a Pendulum. I use this for my sophomores in high

school but don't let that fool you. This can be used at any level where

students can count to twenty and time something.

**Materials Needed**:

pins

various lengths of string

washers (or any of various weights to hang)

clock with second hand (or anything to time with)

a long piece of cardboard or cork-board with a number-line marking off every

five seconds for up to one hundred seconds

**Strategy**:

Tell the students to grab a length of string, tie a washer to one end and a

loop at the other end of the string. Next have the students time the period of

twenty swings. Have the students hang their washer at the spot on the number

line that corresponds with the time they have found. There should be a pattern

that looks something like this:

| | | | | | ||

O O | | | | ||

| | | | ||

O | | | ||

| | | ||

O | | ||

| | ||

| | ||

O | ||

O ||

||

||

O|

O

Ask the students what factors would affect the period of the swing. With

encouragement, I bet they'll come up with length of string, mass, amplitude (how

wide an arc), whether the hand moves or not, and possiblely some others. Break

the students up into groups and have each group investigate these factors by

keeping all factors constant except the one they are investigating. Have each

group report back to the class with their findings.

**Performance Assessment**:

The verbal report to the group may be graded. I believe the ideas of particular

interest include whether or not the group controlled the variables, did they

actually make accurate measurements and present the data (not just guess or

approximate) and then the actual presentation.

**Conclusions**:

1. Mass of the hanging objects does NOT make a difference.

2. The amplitude does NOT make a difference (for amplitudes less than 40

degrees).

3. Length of the string DOES make a difference. There is a formula if you

wish to check it. (Period=2(3.14)Square-root(Length/gravity) or

T=2pi*sqrt(l/g))

4. Small hand movements do not make a difference extreme hand movements will.

**Reference**:

Me! Call me anytime for help.

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