Pendulums are very simple and fun to make! These are basically objects that dangle from a fixed point and that sway back and forth under the action of gravity. While they can be used inside watches to manage the hands or to demonstrate the movement of the earth, they actually make for a fantastic experiment too!
Steps
Part 1 of 3: Building a Pendulum
Step 1. Gather all the material
This experiment can be easily performed at home. Everything you need should already be available in your home. This article describes the construction of a single pendulum, but you can make several of different lengths. For this reason, get some twine longer than 70 cm.
- Get two chairs and a row. You will need these objects to build the "frame" of the pendulum, which will be attached to the ruler placed between the two chairs.
- The scissors will be used to cut the twine. Get duct tape in case it helps, such as if you want to use pennies instead of washers.
- The twine should be at least 70 cm long or even more. You can use string or knitting thread, depending on what you have available.
- The stopwatch allows you to record times, such as the period of the pendulum and how it changes according to the angle or length of the pendulum itself.
- You can use five washers or three pennies as ballast. These are objects that are easily found in the home and whose mass is sufficient for your purpose.
Step 2. Arrange the chairs so that the backrests are facing each other
You need to space them about a meter apart, as you will place the ruler between them. Place them with the seats facing outwards, to prevent them from being in the path of the pendulum.
- Place the ruler on the backrests and make sure it is well centered on the chairs. If the row is not in the right position, your readings will be incorrect.
- If the ruler is stable on the backs of the chairs, you can fix it with adhesive tape.
Step 3. Cut a 70 cm long piece of string
This will be part of your pendulum. All that's left for you to do is attach a weight. If you have decided to make several pendulums of different lengths, you will find that the frequency of each (the number of oscillations in one second) depends on the length of the string.
Knot the string in the center of the row; in this way you are sure that the weight will not hit the chairs
Step 4. Tie five metal washers to the free end of the string
These are the weights that make up the final element of the pendulum. You can replace them with three pennies if you prefer, and in that case you will need to secure them with pieces of tape at the free end.
You will find that a pendulum with a higher ballast will move at the same speed as a pendulum with a lighter weight (you can use a foam ball available at home improvement stores), because the acceleration imparted to both objects does not change regardless of their weight., since it is that of gravity
Part 2 of 3: Using the Pendulum
Step 1. Pull the string so that it is straight and forms a certain angle with the ruler
You can do this by grabbing the weight at the end of the string, where the washers or pennies are. Based on the initial angle, the frequency of the pendulum changes.
For example, if you release the pendulum when the string forms a 90 ° angle with the ruler, you would get a different frequency than what is achieved with a 45 ° release angle
Step 2. Let go of the pendulum
Make sure that the ballast does not hit any object during its swing; if this happens, repeat the experiment. The moment you release the weight, you need to detect the time it takes to travel the trajectory, so try to be ready.
Step 3. Record the times
Start measuring the time taken by the pendulum as soon as you release the weight. When the ballast returns to the starting position it stops the stopwatch. It would be helpful to have an assistant present at this stage so that you can concentrate on the pendulum while he checks the stopwatch.
The time taken by the pendulum to complete an oscillation is called the "period of the pendulum". You can also find the frequency by calculating how many swings are made in a second
Step 4. Release the pendulum once more
Time it again to see if you can get the same values found earlier. Try to respect the same starting inclination and observe any changes.
Step 5. Write down your observations
Write down the times it takes to complete an oscillation and the frequency, so you can have some comparison when you start doing "creative" experiments.
- All this allows you to understand the two main applications of the pendulum. The first concerns the measurement of time, the second instead refers to Foucault's pendulum. In the first case, the pendulum is used to manage the movement of the hands of a clock.
- Foucault's pendulum demonstrates the rotation of the earth. In this case you need a very large pendulum (sometimes as much as two floors of a building) so that it sways for a very long time.
Part 3 of 3: Creative Experiments
Step 1. Cut another segment of rope
If you prepare two or even three pendulums, you can demonstrate the special properties of this object. Take a shorter piece of string than the first one or tie it to a different weight.
- Take a 35 cm long string if you want to understand how the length affects the behavior of the pendulum.
- Place the second segment 20-30 cm from the first, so that they do not collide during the swings.
Step 2. Modify the weight
Try pendulums with different weights to understand how this affects the amplitude of the oscillation and the frequency. It records the times to evaluate the presence of any variation and to quantify it.
Do several repetitions (about five) and average the recorded times or oscillations. This way you get the mean period of the pendulum
Step 3. Change the release angle
Although a slight change in angle does not affect the swing of the pendulum, you will have to try large changes to notice changes in the movement of the ballast. For example, try placing one pendulum at 30 degrees from the ruler and the other at 90 degrees.
Again, as you try different angles, you will have to repeat the experiment several times (about five times) to get a reliable data sample
Step 4. Change the length of the twine
Observe what happens when you release two pendulums of different lengths. Time them to see if the one with the shorter twine is moving faster than the other or if there are no alterations.
Do many repetitions and then find the average value of the periods and frequencies of the pendulum
Advice
- Do not use a very fragile or valuable object as a weight because it could break.
- Choose a piece of string that is considerably longer than the diameter of the weight.
