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Science Rocks!

Pendulum Challenge


your results

Sent in by:
Mallory of Shelton, CT

Make this thing swing back and forth in 5 seconds.

Materials Needed

  • string
  • cup or small pail with a handle
  • sand, for weight
  • something tall and sturdy to hang your pendulum on
  • stop watch or something to keep time



  1. To make the pendulum, tie some string to the handle of a small pail. If you're using a paper cup, make a handle by poking two holes opposite each other close to the lip of the cup. Put a piece of string through the two holes and tie a knot at each end.
  2. Then tie a longer piece of string to the handle of the pail or cup.
  3. Next, tie the other end of the long string to something tall like a branch. Make sure you have enough room to really swing your pendulum back and forth.
  4. Once you fill the pail or cup with some sand your pendulum is ready for experimentation.
  5. Now, see if you can get it to swing back and forth in five seconds. What will you need to change? The weight? The length of the string?

Try this at home. Think of a question that you want answered. Like, what happens if you change the weight of the pendulum? Here's a clue that'll help you answer this question: think about what happens when a big person and a small person swing on a swing set at the same time. Write down what you thought was going to happen and what actually did happen. And then, send your reports to our special feedback area. Every week, we'll publish a whole bunch.

Some of your Results

Chris, age 10 of S. Attleboro, MA wrote:
I put in Salt And It Went Slowly

Simran, age 9 of New York City, NY wrote:
It was so cool. I was aazed that the shorter the string the more time it swings. I didn't think that was going to happen. In fact my science teacher was wacthing your show and she did it with our class.

Suzie, age 5 of IA wrote:
I made them look like flowers, it was cool!

Madison, age 10 of Calgary Place, GA wrote:
I put different weighted objects in and it all made some result different.

Paul, age 8 of Westerville, OH wrote:
It was really cool because I hung it from the celling & put dominoes next to it & every hour a dominoe fell.

Linda, age 13 of Florence, SC wrote:
I didn't try the chalenge yet but I will. Here is another idea: you do the same procedures as if you were doing the pendulum but this time you poke a hole in the bottom. Now you push it foward and watch the floor as the sand pours out. It is really cool.

Kellie, age 11 of Woodland Hills wrote:
Well, what happened was that my teacher did it as a science project in our classroom. We had partners, my partner and I got 28 swings. What we did was we made it short and did not raise it that high.

Zhijiang, age 12 of San Jose, CA wrote:
If you have one of those rotation devices, you can make the same pattern the pendulum makes!

Jason, age 12 of Ruth, MI wrote:
When I tried the pendulum challenge I put pennies in mine and tried to throw them at a target. My pendulum worked really good to. My penny hit the bull's eye "After a while".

Magali, age 11 of Salt Lake City, UT wrote:
It did circals 2 times and then it made the flower.

Robin, age 11 of Deer Lodge, TN wrote:
It will go in a circle then it goes to the right and to the left.

Christian, age 5 of Birmingham, AL wrote:
We tried it using my mama's necklace first, then on the ZOOM website. And I think it's pretty cool and that you might like my idea. You'll need a pen, some string, and a paper cup. Use the pen to poke a hole in the cup, then tie the string around the pen so the cup is hanging at the end and the pen is at the top. Now you have your own pendulum to experiment with and make predictions to check against the ZOOM website. That's it!

Allison, age 13 of Chicago, IL wrote:
I measured the amount of swings in 20 seconds. I used all of your varablies that you have on the site. The only thing that changed the amount of swings was the length of the string. As the string got shorter the amount of swings increased. If you want to try changing something else you can change the thing at the end of the string. Also known as the Bob mass.

Roxi, age 8 of Ellicott City, MD wrote:
The lenth of string made a significant differance. Not the thickness of the string or the weight of the bob.

Grace, age 12 of Perry, MI wrote:
When I put a lot of sand in it it went faster, also when the angle got greater the circles got bigger.

John, age 10 of Baldwin, NY wrote:
I found that the the weight played no role in the period of the pendulum, rather the length, proved by Newton's second law of rotational systems. In order to make the pendulum swing for 5 seconds, I would have to adjust the length of the string to make the equation, Time(for one oscillation)=2π √(length/gravitational acceleration), so that Time would equal 5 seconds. Now, plugging it into the equation, we have 5sec= 2π √(length/9. 81m/s². After solving for length, and arriving at an answer of 6. 21 m, I made my string's length accordingly, placed a fishing weight on the end, and finally timed it, and got exactly 5 seconds.

Thomas, age 11 of West Melbourne, FL wrote:
At first I used 5 feet of string and 1 pound of sand. But it worked with 1 pound of sand and 3 feet of string.

Krisina, age 10 of New Haven, CT wrote:
When I tried to do the Pedulum Challenge, I went outside and I made the Pendulum, then I stuck it on a branch, at first it swung for 7 seconds. But when I cut the string, 5 inches shorter, it went for 5 seconds!!! I used a plastic cup and filled it up with water.

Shelby of San Luis Obispo, CA wrote:
I went on to the home page and made a perfect circle by setting the string length to twenty one meters. The gravity was on the moon or 1. 626m/s2. The rotation was 3 degrees/s. The starting angle was sixty degrees.

Holly, age 8 of Athens, GA wrote:
My whole family tried the Pendulum of Fear. It scared us but no one was hit. My brother wanted me to make him one in his room today. It was fun!

Dustin, age 6 of Knoxville, TN wrote:
The one where you hang a cup from a branch with a string. My Sister Monica helped me, and we made the pendulum swing for 10 seconds.

Ashley, age 9 of Northampton wrote:
I put some sand and dirt in mine and it swung like crazy.

Meagan, age 13 of Zeeland, MI wrote:
I experimented with the pendelum, and I found out that it is really hard to make a perfect circle. I tried a lot and got really close. I also found out that when you change the gravity, the whole design and size changes. For an episode, I think it would be cool to expiriment with the pendulum and show people how it works. Also, can you show us how to make our own pendulum to expiriment with at home?

Tyson, age 12 of Jacksonville, FL wrote:
I put 2 cups of dirt in mine. It made some cool shapes. Then I put in 2 more cups of dirt and it barely moved.

Emily, age 11 of Richmond, KY wrote:
I put 2 cups of sand in mine and it swung a lot slow but when I put a cup of sand it went faster. It made a star. When I swung it another way it made a hart. That is what happened when I made one.

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