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# Galileo: A Different Thinker

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### Overview

In this lesson, students examine four of the experiments that Galileo used to discover the effects of gravity and inertia on moving objects. Galileo challenged the thinking of his day by studying falling objects, projectiles, objects rolling down inclined planes, and swinging pendulums. His observations are the basis for much of current classical physics. Students will use a combination of interactive activities, video segments, and readings to study Galileo's ideas.

### Objectives

• Discover that the rate at which an object falls is independent of its mass
• Understand that horizontal motion does not affect the rate at which an object falls vertically
• Learn that the speed of a falling ball is dependent on the vertical height from which it is dropped
• Discover that the time a ball takes to reach the bottom of an inclined plane is dependent on the slope of the plane
• Understand that the period of a pendulum's swinging motion is dependent on the length of the string

### Suggested Time

• Three class periods

### Materials

• string
• washers or other small masses that can be easily tied to the string
• something tall and sturdy to hang the pendulum on
• stop watch or something to keep time

### Part I: Horizontal and Vertical Motion

1. Have students read the introduction to the Galileo: His Experiments interactive activity and discuss the following:

• What do falling objects, inclined planes, and pendulums have in common?
• What phenomena in our daily lives are similar to the objects in Galileo's experiments?
• Why were Galileo's thoughts about science so revolutionary in his day?

2. Have students do the Falling Objects experiment in the Galileo: His Experiments interactive activity. Discuss the effect of mass on the rate of a falling body. Have students brainstorm several daily events in which one can observe the independence of mass on acceleration of a falling object due to gravity.

3. Have students do the Projectiles experiment in the Galileo: His Experiments interactive activity. Discuss the horizontal and vertical components of motion for a projectile. Have students brainstorm several daily events in which one can observe projectile motion.

4. Show the video Galileo's Thought Experiment. Discuss the concept of frames of reference and other examples of relative motion that are analogous to the horse rider dropping a ball. Examples include a passenger in a train or car throwing a ball up in the air.

### Part II: Inclined Planes

5. Have students do the Inclined Planes experiment in the Galileo: His Experiments interactive activity. Discuss the effects of height and inclination on the velocity of and length of time traveled by an object rolling down an inclined plane. Have students brainstorm several daily events in which one can observe objects moving down inclined planes.

6. Show the video Galileo's Inclined Plane. Have students discuss why Galileo used inclined planes to study the effects of gravity and what he discovered through his research.

### Part III: Pendulums

7. Have students brainstorm several daily events in which one can observe pendular motion. Have them predict which variables determine the period of the swing.

8. Have students do the Pendulums experiment in the Galileo: His Experiments interactive activity. Discuss the effects of the mass of the swinging object and the length of the string on the period of the swing.

9. Distribute the materials and instructions for the Experimenting with a Pendulum activity. Have students test variables to determine which affect the period of the swinging motion. For example, while keeping the length of the string constant, have students vary the mass of the swinging object by using 1, 2, and then 3 washers at the end of the string. Then, while keeping the mass constant, have them vary the length of the string. For each trial, have them measure the period of the swing -- one complete back-and-forth swing of the pendulum. It is typically easiest to measure the time for 10 swings and divide by 10 to get the average period per swing.

### Check for Understanding

Have students discuss the following:

• In what ways are Galileo's experiments helpful in understanding the relationship between mass, height, velocity, and gravity?
• To measure the motion of an object rolling down an inclined plane, Galileo put markers along the plane to identify the points where the ball passed at equal intervals of time. Why weren't the markers placed at equal distances along the plane?
• Suppose a projectile is fired parallel to the ground and another is dropped straight down at the same time. Which object will land first? Why?
• Does the period of a pendulum depend on the mass of the swinging object? Explain how this result relates to Galileo's other experiments.

### Related Resources to Check Out

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