What is a pendulum used for?
Know that a pendulum is a weight hanging freely at the end of a string. Before you start using a pendulum, you need to know what it is and how it works. Luckily, a pendulum is no more than a hanging weight allowed to swing back and forth. The string is attached to a fixed point so that only the weight and string are moving.
- Hold the end of pendant necklace or yo-yo between your fingers and move the "weight" at the bottom. You've made your first pendulum!
- A common example of a pendulum is the large swinging weight in a grandfather clock.
AdTo use a pendulum, pull the weight back and let go. Make sure you keep the string taught and release the weight without pushing it. The weight will swing back and forth, returning to roughly the same height you dropped it from.
- A pendulum will swing forever if nothing happens to slow it down or change its direction.
- In reality, outside forces like friction and air resistance will slow down a pendulum.
- Tie one end of a string to the middle of a yardstick or poll.
- Tie the opposite end to a battery or other small weight.
- Balance the yardstick on the backs of two identical chairs so that the battery hangs freely between them and can swing without hitting anything.
- Pick up the battery, keeping the string taut, and release it so that it swings back and forth.
- Amplitude: The highest point the pendulum reaches.
- Bob: Another name for the weight at the end of the pendulum.
- Equilibrium: The center point of a pendulum; where the weight rests when it is not moving.
- Frequency: The number of times a pendulum swings back and forth in a set amount of time.
- Period: The amount of time it takes a moving pendulum to return to the same spot.
Method 2Using Pendulums to Teach Basic Physics
- Know that pendulum experiments are a great way to teach the scientific method. The scientific method has been the backbone of scientific research since the ancient Greeks, and pendulums are easy to tinker with and see instant results. When conducting any of the following experiments, take the time to formulate a hypothesis, talk about which variable you are testing, and compare the results.
- Always do the experiment 5-6 times to make sure your results are consistent.
- Remember to only try one experiment at a time- otherwise you won't know what changed the pendulum's swing.
- Change the weight at the end of the string to teach about gravity. One of the simplest ways to learn about gravity's effects is through a pendulum, and the results may surprise you. To see the effects of gravity:
- Pull back the pendulum 10 centimeters and release it.
- Use a stopwatch to time the period of the pendulum. Repeat 5-10 times.
- Add a heavier bob to the pendulum and repeat the experiment.
- The period and frequency will be exactly the same! This is because gravity affects all weights equally. A penny and a brick, for example, will fall at the same speed.
- Change where you drop the weight to learn about amplitude. When you pull the string higher you've increased the amplitude, or high point, of the pendulum. But does that change how fast the pendulum returns to your hand? Repeat the above experiment, but pull the pendulum back 20 centimeters this time instead of changing the weight.
- If you did everything correctly, the pendulum period will not change.
- Changing amplitude does not change frequency, a fact that will come in handy in trigonometry class, the science of sound, and many other fields.
- Change the length of the string. Repeat the experiment above, but instead of changing how much weight you've added or how high you've dropped it, use a much shorter or longer string.
- This time you will definitely notice a change. In fact, changing the length of the string is the only thing that will change the period and frequency of a pendulum.
- Dive deeper into pendulum physics to learn about inertia, energy transfer, and acceleration. For older students or aspiring physicists, pendulums are a great way to learn the relationships between acceleration, friction, and trigonometry . Search for "pendulum equations, " or devise your own experiments to find them. Some questions to consider:
- How fast is the bob moving at the lowest point? How do you find the speed of the bob at any point?
- How much kinetic energy does the bob have at any point in the pendulum? For help, use the equation: Kinetic Energy = .5 x Mass of Bob x Velocity2
- How can you predict the period of a pendulum based on the string's length?
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