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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

Ariel, age 10 of San Diego, CA wrote:
Im in fifth grade and my analysis for my Science class said " Increasing the lenght of the Pendulum decreases the number of cycles. Lesser the length = more cycles. My string was 13 cm long and I got an average of 19 cycles in 15 seconds."

Masha, age 10 of Orlando, FL wrote:
When I did the Pendulum Challenge, I discovered that the only factor that does change the number of cycles in which the pendulum performs is the length of the string.

Jill of Denver wrote:
When I did the Pendulum Challenge, it didn't work so well! I put about 4 1/2 cups of sand in it and it only went for3. 9 seconds! I had it at five feet and it still wouldn't go for five seconds!!! How much sand did you guys have? For anyone trying this experiment: tie on you pendulum to something REALLY tall, your gunna need it! Also have someone else help you with the timing and stuff. Make sure you have at least 8 cups of sand, YOU WILL USE ALL OF IT!!! Lastly, do it fairly and a number of times to find an average! DO outside with a cover on it because sand will fall out otherwise! I hope this helped!!! Good luck to all!!!

Chelsea, age 11 of Phildelphia, PA wrote:
it swings perfect lee it was for 5 seconds it was awesome I had it for 2 days it was crazy the sand come out so I had to cover it with a paper did I have to?

Dana, age 8 of Las Vegas, NV wrote:
When I first tried the Pendulum Challenge, the swing went back and forth in a total of 8 seconds, but when I tried it the second time, this time at a higher elevation, it only took 5 seconds to go back and forth, but then I looked at the record, and then I decided that I wanted to beat the record, sooo bad so I tried it a third time and, I couldn't believe it, but I made the swing go back and forth in only 3 seconds!!!

Haley, age 9 of Sacramento, CA wrote:
When I let go of the string, it drew a beautiful flower. But the second one was a 3-D type!

ZOOM Fan of Orlando, FL wrote:
it didnt work at all. it just spun on the string. any one know a way to improve it?

Marci of Mendoza, Argentina wrote:
Salt Pendulum: I did it with my ESL kindergarten class, ages 5-7, and I coated the student's paper with glue, I also used different color papers, after we left the pendulum move for a little while over each paper, we shook it and the designes stayed so they could take their experiment home. It was a blast.

Katrina, age 13 of North Conway, NH wrote:
well when I did it, it didn't really work but it kind of did also it just stayed in place and salt just fell out but it did spin a little but barely

Steven of WI wrote:
I did in school and we tested it! How can it make a shape? I'm in 6th grade so look whats coming to you!

Gimmy, age 14 of Dubai, UAE wrote:
Actually it did work but it wasn't accurate enough. I and my friends had a lot fun while setting this experiment up in our school for the small children to explain how does the pendulum work.

Hannah, age 8 of Mansfield, OH wrote:
it went around five times in one secend

Stephanie, age 12 of Macon wrote:
it just made a pretty little flower and it was very pretty and I want to let you know that I'm your biggest fan

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.

not yet implemented