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Author:
Jack Bauer

Student Exploration: Energy of a Pendulum

Vocabulary: conservation of energy, gravitational potential energy, kinetic energy, pendulum, potential energy, velocity

Prior Knowledge Questions (Do these BEFORE using the Gizmo.)

A toy car is about to roll down a track, as shown below. At what point do you think the car will reach its greatest speed?

Mark this point on the image.

A pendulum consists of a weight that is suspended from a pivot. At what point will the pendulum below move fastest?

Mark this point on the image.

What do these two situations have in common?

Gizmo Warm-up

Objects have several types of energy. Potential energy depends on an object’s position or shape. Kinetic energy is the energy of movement. The Energy of a Pendulum Gizmo™ allows you to explore how the amounts of these types++- of energy change for a pendulum in motion.On the DESCRIPTION pane, change the initial angle (θ) to 40 degrees. Click Play (). How does the velocity (speed and direction) of the pendulum change as it swings from right to left?

On the image at right, mark the point where the pendulum swings fastest with an X. Then, circle the two points where the velocity is zero.

Activity A:

Potential and kinetic energy

Get the Gizmo ready:

Click Reset ().

Check that m is 0.5 kg, L is 2.0 m, g is 9.8 m/s2, and θ is 40 degrees.

Introduction: An object that is a certain height (h) above the ground has the potential to do work, and therefore has potential energy. This type of potential energy is called gravitational potential energy (GPE, or PE for short). The unit of energy is the joule (J).

Question: How are potential and kinetic energy related?

Observe: Select the BAR CHART tab. Click Play and observe. What do you notice about the gravitational potential energy (PE), kinetic energy (KE), and total energy (TE)?

Measure: Click Reset. Turn on Show numerical values.

What is the gravitational potential energy?

What is the kinetic energy?

What is the total energy?

Measure: Click Play, and then try to click Pause () when the pendulum is in the middle of its swing. (This might require several tries.)

What is the gravitational potential energy now?

What is the kinetic energy now?

What is the total energy?

Analyze: At any given time, what can you say about the total energy of the pendulum?

This illustrates the principle of conservation of energy. In a closed system, energy can be converted from one form to another, but the total amount of energy remains the same.

(Activity A continued on next page)

Activity A (continued from previous page)

Tutorial