This is because the swinging motion of a pendulum is due to the force of gravity generated by the earth's size. Other factors, including a pendulum's length, can also affect its motion. Background A pendulum is an object hung from a fixed point that swings back and forth under the action of gravity. In the example of the playground swing, the swing is supported by chains that are attached to fixed points at the top of the swing set.
When the swing is raised and released, it will move freely back and forth due to the force of gravity on it. The swing continues moving back and forth without any extra outside help until friction between the air and the swing and between the chains and the attachment points slows it down and eventually stops it.
The time it takes a pendulum to swing back to its original position is called the period of the pendulum. For example, this is the time it takes a child being pushed in a swing to be pushed and then return back for another push. The period of the pendulum depends on the force of gravity, as well as the length of the pendulum. Space them about one meter apart. Lay the meter stick on the backs of the two chairs, centered on the back of each.
Cut a second piece of string to a length of 35 cm. Tie one end of both strings to the meter stick, toward the middle of the stick. Space the strings about 20 to 30 cm apart on the meter stick. Alternatively, if you are using pennies and tape, securely tape three pennies to the free end of each string.
Drop the longer pendulum and, at the same time, have the assistant start the stopwatch. Then have the assistant stop the stopwatch when the pendulum returns back to its original position. If the pendulum hit anything as it swung, such as the wall, readjust your setup and try timing the pendulum again. How long does it take the longer pendulum to swing back to its original position? Now, based on these observations, determine what conclusions students can make about the nature of gravity. Students should conclude that gravitational force acting upon an object changes its speed or direction of motion, or both.
If the force acts toward a single center, the object's path may curve into an orbit around the center. Assess the students' understanding by having them explore the Pendulums on the Moon lesson, found on the DiscoverySchool.
Students should click the link for "online Moon Pendulum," found under the "Procedure" section of the lesson. This activity simulates the gravitational force on the moon. Students should experiment for approximately minutes, changing the mass, length, and angle to observe the effect it has on the pendulum.
Make Coupled Resonant Pendulums This experiment demonstrates that two pendulums suspended from a common support will swing back and forth in intriguing patterns if the support allows the motion of one pendulum to influence the motion of the other. The directions for this experiment are on the Exploratorium website.
Measuring Falling Time When Galileo was studying medicine at the University of Pisa, he noticed something interesting about the periods of a pendulum. In church one day, he watched a chandelier swing back and forth in what seemed like a steady pattern of swings.
He timed each swing and discovered that each period was the same length same amount of time. In the previous activity, students measured the periods of their pendulums using either digital watches or stopwatches.
Galileo did not have these tools, so he used his pulse. In this activity, students will time the periods of their pendulums using their pulses and compare their results with those obtained with a watch. Show students how to find their pulse by pressing two fingers on the artery next to their wrist. Make sure that students have been at rest for several minutes before doing this so that they can obtain a steady pulse rate. Working in teams, have one student set the pendulum in motion while another measures the pulse beats that occur during five complete swings and then ten complete swings.
Students should reproduce the distances they used in the earlier experiment, Testing Falling, for the amplitude and length of string. Record the number of pulse beats. Repeat this procedure with different students measuring their pulse rates. Then have students measure and record five complete swings and ten complete swings using a stopwatch or digital watch. Share each group's results with the entire class. How do the pulse beat measurements compare with those timed with a watch?
What are the advantages of using a stopwatch or digital watch over counting pulse beats as a method of timing? See the Tool. See the Collection. See the Lesson. Where do you see pendulums in everyday life? How are they useful? Pendulums can be found in swing sets, grandfather clocks, swinging a baseball bat, and the circus trapeze. Pendulums are useful in timekeeping because varying the length of the pendulum can change the frequency.
After your discussion, have students explore these websites: Pendulum What is a Pendulum? Explain the features of this demonstration to your students: In this demonstration, you can vary the length of the pendulum and the acceleration of gravity by entering numerical values or by moving the slide bar.
To participate in this demonstration, students should follow these steps: Press the "Start" button of the stopwatch just at the moment when the pendulum is going through its deepest point. Count "one" when it goes again through its deepest point coming from the same side. Repeat counting until "ten. Dividing the time in the display by ten yields the period of oscillation. Ask students: What is meant by the period of oscillation? It is a way of measuring the back and forth swing of the pendulum.
How does changing the length of the bob affect the period of oscillation? The longer the length of the bob, the longer the period of oscillation will be. When the swing is raised and released, it will move freely back and forth due to the force of gravity on it.
The swing continues moving back and forth without any extra outside help until friction between the air and the swing and between the chains and the attachment points slows it down and eventually stops it. Make sure the clock hands are not touching the glass. The reason a clock pendulum often stops swinging, after being moved, is because the clock case now leans at a slightly different angle then it did at its former location. The pendulum bob stops oscillating after sometime due to the air resistance offered to it and due to the friction at the point of support.
The same thing happens in freefall motion, where all things of all weights fall at the same rate. The period of a pendulum does not depend on the mass of the ball, but only on the length of the string.
Two pendula with different masses but the same length will have the same period. Two pendula with different lengths will different periods; the pendulum with the longer string will have the longer period. When you add a weight to the bottom of the pendulum on the right, you make it heavier.
When you add a weight to the middle of the other pendulum, however, you effectively make it shorter. The gravity of pendulum never stops, it always accelerates. So the gravity affects the pendulum acceleration and speed.
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