Swing Pendulum Swing

Learning Objectives

Students examine the motion of a pendulum and come to understand that the longer the string of the pendulum, the fewer the number of swings in a given time interval. They see that changing the weight on the pendulum does not have an effect on the period.

Associated Curriculum Topic

Systems in Action

Materials

• string
• pencil
• tape
• objects that can be used as masses (i.e. fishing weights, clay, erasers, etc.)
• stop watch (or wall clock)

Introduction/Motivation

In this activity, students will examine the motion of a pendulum. If they have ever played on a swing set, they are already familiar with some of the ways that a pendulum can move. In this lab, students will examine specific factors that might affect the way a pendulum swings. In particular, students will time a pendulum swinging back and forth, and see what factors make it speed up and what conditions make it slow down.

Procedure

• measure and mark a 110 cm long piece of string at every 10 cm interval
• tie the string to the mass (one fishing weight, an eraser, etc.)
• tape the string to a pencil at the 10 cm mark
• place two desks close enough that the pencil can span the gap between desks and the mass can hang below it
• pull pendulum back to 45 degrees, and count the number of times it swings back to its original starting point in 30 seconds
• now hang the object from the 20 cm mark and repeat
• repeat at every 10 cm interval until 50 cm
• have students create a graph with number of swings on the vertical axis and length of string on the horizontal axis
• add some more mass to the pendulum and repeat the procedure
• students should be able to predict results for 60 to 100 cm lengths based on their observations – have them record their predictions on their worksheets and then test and record their results

Investigating Questions

• What effect does string length have on the number of oscillations observed in 30 seconds?
• What effect does mass have on the number of oscillations observed in 30 seconds?
• Where might you find a pendulum in your everyday lives?
• What length of string would result in a pendulum that swings exactly 60 times per minute? How would this be useful? (Answer: A pendulum could be used as a clock if each swing took one second

Adapted from Teach Engineering