Jump to main content

Centripetal Force

904 reviews


What keeps you in your seat of a giant loop-de-loop roller coaster? Surprisingly, it is not the seatbelt but the seat! It works because of something called centripetal force and it does much more than make a great roller coaster. It keeps a satellite in orbit and you in your bicycle seat during a turn. How does it work?


Areas of Science
Time Required
Short (2-5 days)
Material Availability
Readily available
Very Low (under $20)
Adult supervision is required for making the JELL-O. Be careful when working with the boiling water.
Sara Agee, Ph.D., Science Buddies
Teisha Rowland, Ph.D., Science Buddies
  • JELL-O is a registered trademark of Kraft Foods. All rights reserved.


Investigate the movement of an object during circular motion and determine what the centripetal force is.


You have probably heard the famous story about Sir Isaac Newton and the discovery of gravity where an apple fell on his head while he was sitting beneath an apple tree. Whether or not this story is true, Newton was a careful observer of the world around him. His genius was to use mathematics and science to describe natural phenomenon which, at the time, were not understood.

Newton made many discoveries: the laws of gravity, colors, prisms, advanced mathematics and motion. Newton's Three Laws of Motion are still in use today, and these principles can be found in almost any modern moving technology. Newton's First Law of Motion is often stated as "objects at rest stay at rest, and objects in motion stay in motion." This simply means that once you are still, it is hard to get moving, and once you are moving, it is hard to stay still.

Newton discovered that to get an object to move, the object must experience a force that makes it move in a certain direction. Once the object experiences this force, it is set in motion and will continue this motion until it experiences an opposite force that causes the motion to stop. You have felt this phenomenon when riding in a car. When the car starts moving you rock backward because your body wants to stay in its stationary position. But after you are moving, if the car suddenly stops you will rock forward because your body wants to keep moving forward at the same speed and direction.

This example describes what happens when you experience motion in a straight line, but what about other types of movements? Newton realized that when things move in a circle that the object wants to move out, away from the center of the circle. For example, when you are riding in a car and it makes a turn, you experience this circular motion as your body moves to the outside of the turn, away from the direction of the turn.

So if your body wants to move away from the center of the circle, what keeps you moving in a circular path? This force is what Newton described as centripetal force, or a force that makes an object move, or accelerate, towards the center of a circle. Without centripetal force the object would move in a line. In the car example, the weight of the car, gravity, and the friction of the road keep you in your seat moving in a circle.

Now back to the loop-de-loop rollercoaster. The tracks are moving in a circle, and we move along with it, but what is keeping us in our seat? Gravity is a force that pushes us down toward the ground, which may help us stay in our seat at the bottom of the loop, but it probably does not help us stay in our seat at the top of the loop! The force from our seat belt may help us stay in our seat, but just mostly at the top of the loop. Centripetal force is a force that must be constantly pulling us towards the center of the loop, not just at the bottom or top of the loop. What other forces are acting on us while we move in the loop? Could it be the force of the seat itself that is holding us in our seat? Which force is the centripetal force when we ride in the loop-de-loop?

In this physics science project, you will use plastic cups, marbles, and two different colors of JELL-O® to investigate the movement of an object during circular motion and determine what the centripetal force is that keeps the object moving in a circular way. Which way will the marble go?

Terms and Concepts



Materials and Equipment

Experimental Procedure

Making the Centripetal Force Test Chambers

In this part of the science project, you will make 6 centripetal force test chambers using JELL-O, cups, and marbles. You will want to make more than one to have replicates, or copies, of your data.
  1. Make a package of JELL-O by following the instructions on the box, except use more cold water than is recommended.
    1. Making JELL-O using more water will make it less thick and liquidier. This will make it easier for the marble to move when you test it later.
    2. On the stove in the cooking pot, have an adult help you boil the appropriate amount of water according to the instructions on the box.
    3. Continue following the box's instructions by adding the JELL-O mix to the boiling water. Stir the JELL-O mix in the water for 2 minutes while keeping the pot on the hot burner.
    4. After stirring for 2 minutes, the JELL-O should be completely dissolved and no particles of JELL-O powder should be visible. It should look clear. The JELL-O should also barely start boiling again.
    5. Take the JELL-O off of the hot burner and add 1.5 times the amount of cold water that is recommended on the box's instructions. Use cold tap water and stir it in as it is added.
      1. For example, if the instructions say to use 1 cup of cold water, use 1.5 cups of cold water instead.
  2. Pour the JELL-O into six of the plastic cups, filling each cup a little less than halfway full. These will be your centripetal force test chambers.
    1. Use a permanent marker to label these cups #1-6.
  3. Place the cups in the refrigerator and refrigerate them for 4 hours.
    1. Because you used more water than is recommended in the box's instructions, the JELL-O will not be very firm after 4 hours, but it should be firm enough to support the marble in the next step.
  4. In each cup, place a marble on the top of the JELL-O in the center of the cup. Gently press into the JELL-O just until the marble is secure and will not move around. Why do you think it is important that the JELL-O is firm enough to support the weight of the marble?
  5. Make the second batch of JELL-O by preparing it as you did in step 1. Why do you think the second batch should be a different color from the first?
  6. After adding the cold tap water to the JELL-O, place an oven mitt in the refrigerator and have an adult help you place the pot with the JELL-O on the oven mitt. Refrigerate the pot of JELL-O for 30 minutes.
    1. This second batch of JELL-O will be added to the JELL-O already in the plastic cups. However, if the second batch of JELL-O is not refrigerated before it is added, it may be too hot and melt the first layer of JELL-O.
  7. After refrigerating the pot of JELL-O, slowly and carefully pour the JELL-O into the cups, covering the first layer of JELL-O and the marble, until the cups are almost full. Leave about 2.5 centimeters (cm) (1 inch) at the top of the cups.
    1. It is important to slowly and carefully pour the second layer of JELL-O on top of the first layer because otherwise the second layer may damage the first layer.
    2. Do not worry if the two layers of JELL-O mix together a little where they meet. However, check to make sure that the marble stays roughly in the middle, between the two layers. Do not use any cups in which the marble is not near the middle.
      1. If multiple cups have marbles that are not near the middle, try repeating steps 1-7 but use less cold water in step 1e, such as 1.25 cups instead of 1.5 cups.
    3. Your cups should look similar to the one in Figure 1, although your layers of JELL-O may be different colors.
A cup contains two layers of different colored JELL-O that has a marble trapped between the two layers

Figure 1. Once you have poured two layers of JELL-O into your cups, they should look similar to this one, with the marble in between the two layers.

  1. Place the cups in the refrigerator and refrigerate them for 4 hours.
  2. While your JELL-O solidifies, prepare your centripetal force generator. You will be testing your test chambers inside of the generator.
    1. Take an empty plastic cup and use the scissors or one-hole puncher to make a small hole about 2.5 cm (1 inch) from the top rim of the cup. Make a second hole on the opposite side of the cup.
    2. Put a small piece of electrical tape or duct tape on the edge of the cup, just above each hole. Fold over the tape so it is on the outside and inside of the cup, but not blocking the holes. This will help prevent the string, which you will attach next, from detaching.
    3. Attach the string to the top of the cup, tying one end of the string through one of the holes at the cup's top and the other end through the other hole.
    4. Your cup should now look like the one in Figure 2. This cup will be your centripetal force generator. Test to make sure that the string is strongly attached to the cup by holding on to the string and pulling down on the cup.
A plastic cup is given a handle by taping a piece of string across the top

Figure 2. Prepare your centripetal force generator cup, as shown here, by making two holes in the top of the cup, placing electrical or duct tape above the holes, and tying string through the holes.

Testing the Centripetal Force Test Chambers

  1. After refrigerating the cups, take one of your test chambers and place it in the centripetal force generator by stacking the plastic cup with the JELL-O into the plastic cup with the string.
    1. Do not use any cups in which the marble is not near the middle. If multiple cups have marbles that are not near the middle, try repeating the section titled "Making the Centripetal Force Test Chambers" but this time use less cold water when making the JELL-O in steps 1e and 5, such as 1.25 cups instead of 1.5 cups.
  2. Take the stacked cups outside to an open area.
  3. Now hold the string and quickly twirl the cup around your head for 20 revolutions, counting each time the cup makes a complete circle, making as wide a circle as you feel comfortable with. You must spin the cup hard and fast to get enough centripetal force for the marble to move!
  4. After 20 revolutions, stop spinning and remove the inner cup from the outer cup.
  5. Observe the JELL-O, and the position of the marble relative to the two different colors of JELL-O. Remember that the marble started out right at the dividing line between the two colors. Where did the marble move to? Make observations, drawings, and record data in a data table in your lab notebook similar to Table 1.
    1. If you have trouble locating the marble, try backlighting the marble by shining a flashlight through the back of the cup, toward you.

      Test ChamberWho swung it? Where did the marble move to? Was the test chamber spun more than once to move the marble? Other Observations
      #4Adult helper   
      #5Adult helper   
      #6Adult helper   

      Table 1. In your lab notebook, make a table like this one to record your observations and data.
    2. If the marble did not move, the JELL-O may be too firm. First try spinning it around for 20 revolutions again, but this time spin it harder.
    3. If the marble has still not moved, either let the cups sit out at room temperature overnight to soften the JELL-O or repeat the section titled "Making the Centripetal Force Test Chambers" but this time use more cold water when making the JELL-O in steps 1e and 5.
  6. Repeat steps 1-5 with two other cups. Then have your adult helper repeat steps 1-5 with a total of three cups.
    1. If your adult helper spins the cup harder than you did, how do you think this will affect how the marble travels?
  7. Did you notice any patterns of movement? Did the marbles always move in the same direction? Did they move in the direction you thought they would? How far did they move? Did they move differently when you spun the cups compared to when your adult helper spun them?
    1. Based on where the marbles went during circular motion, what do you think is the centripetal force that keeps the marbles moving in a circular way, and prevents them from flying off in a straight line?
icon scientific method

Ask an Expert

Do you have specific questions about your science project? Our team of volunteer scientists can help. Our Experts won't do the work for you, but they will make suggestions, offer guidance, and help you troubleshoot.


  • One of Newton's other laws says that there is a relationship between the motion of an object and its mass. Try a similar science project with small objects of different weights to see if this has an effect on the amount of movement an object makes due to a centripetal force. Instead of marbles, try lead fishing weights, beans, quarters, beads, etc. Do you notice a difference in motion between objects of different weights or sizes?
  • How fast did you swing your centripetal force generator? Is there a relationship between speed and circular motion? Try using a metronome to guide your speed of rotation, setting the metronome at fast and slow speeds. Do the cups move differently at faster speeds than they do at slower speeds?
  • There are many ways to experience Newtonian motion. Try taking some of your pre-made test chambers with you for some on-site experimentation. What happens to the marble when you take it on a swing, slide, merry-go-round, rollercoaster, car ride, bike ride, rollercoaster, or anywhere else you are curious to find out about?


If you like this project, you might enjoy exploring these related careers:

Career Profile
Mechanical engineers are part of your everyday life, designing the spoon you used to eat your breakfast, your breakfast's packaging, the flip-top cap on your toothpaste tube, the zipper on your jacket, the car, bike, or bus you took to school, the chair you sat in, the door handle you grasped and the hinges it opened on, and the ballpoint pen you used to take your test. Virtually every object that you see around you has passed through the hands of a mechanical engineer. Consequently, their… Read more
Career Profile
Physicists have a big goal in mind—to understand the nature of the entire universe and everything in it! To reach that goal, they observe and measure natural events seen on Earth and in the universe, and then develop theories, using mathematics, to explain why those phenomena occur. Physicists take on the challenge of explaining events that happen on the grandest scale imaginable to those that happen at the level of the smallest atomic particles. Their theories are then applied to… Read more
Career Profile
Our universe is full of matter and energy, and how that matter and energy moves and interacts in space and time is the subject of physics. Physics teachers spend their days showing and explaining the marvels of physics, which underlies all the other science subjects, including biology, chemistry, Earth and space science. Their work serves to develop the next generation of scientists and engineers, including all healthcare professionals. They also help all students better understand their… Read more
Career Profile
You use mechanical devices every day—to zip and snap your clothing, open doors, refrigerate and cook your food, get clean water, heat your home, play music, surf the Internet, travel around, and even to brush your teeth. Virtually every object that you see around has been mechanically engineered or designed at some point, requiring the skills of mechanical engineering technicians to create drawings of the product, or to build and test models of the product to find the best design. Read more

News Feed on This Topic

, ,

Cite This Page

General citation information is provided here. Be sure to check the formatting, including capitalization, for the method you are using and update your citation, as needed.

MLA Style

Science Buddies Staff. "Centripetal Force." Science Buddies, 8 May 2023, https://www.sciencebuddies.org/science-fair-projects/project-ideas/Phys_p018/physics/centripetal-force. Accessed 24 Feb. 2024.

APA Style

Science Buddies Staff. (2023, May 8). Centripetal Force. Retrieved from https://www.sciencebuddies.org/science-fair-projects/project-ideas/Phys_p018/physics/centripetal-force

Last edit date: 2023-05-08
Free science fair projects.