Can you pick up a ball with an open jar? It doesn’t seem possible at first, but with the magic of centripetal force, you’ll be able to make it happen!
This quick science experiment only requires two items and a little practice. Helpful tips, a demonstration video, printable instructions and a simple explanation of how it works are included with this super fun experiment.
- Small Ball (we used a bouncy ball)
- Jar with a mouth that is larger than the ball (we used a pint canning jar)
Step 1 – Gather a small ball and a jar with a mouth that is bigger than the ball. Set a ball on the table and ask some questions. Without using your hands to touch the ball, do you think it is possible to pick up the ball with the jar?
Helpful Tip: Bouncy balls are great for this experiment, as are pint-sized canning jars.
Step 2 – Next, attempt the pick up the ball using the jar. You notice that it is difficult to do so, but you may be able to figure out the experiment with a little trial and error.
If you can’t pick up the ball, start again. This time place the jar over the ball on a hard surface.
Step 3 – Next, begin to move the jar in circular motions around the ball. The ball will eventually begin moving along the rim of the jar. As this happens, begin moving the jar faster and faster until the ball moves up into the jar.
Helpful Tip: This step will take practice and patience, but if you take your time you will eventually get the ball to move up into the glass.
Step 4 – Continue moving the jar in a circular motion and lift it off the table. You have just successfully picked up the bar, using just the jar. Now, take a moment to write down your observations. Do you know the reason why you were able to pick up the ball with the jar? Find out the answer in the how does this experiment work section below.
Helpful Tip: While this experiment looks easy to perform, it does take practice to get it down. Don’t get discouraged if you can’t do it the first time. Instead, keep practicing and you will eventually be able to pick up the ball.
When you spin the jar in a circle, the ball will begin to move in a circle along with the jar. This is because the ball is accelerating due to its constant change in direction. With the ball and jar both moving in the same direction, the jar pushes against the ball and the ball pushes against the jar. This creates a centripetal force which is greater than the force of gravity pulling down on the ball.
Centripetal force is any force that causes an object to move in a circular path. This centripetal force allows you to pick up the ball with the jar. Newton’s First Law of Motion states that an object at rest will stay at rest, and an object in motion will stay in motion unless acted on by an outside force. As long as you continue to spin the jar at a constant rate, the ball will continue to spin at the same rate allowing you to pick up the ball with the jar.
If you stop (or slow down) the circular motion of the jar, the force of gravity will become greater than the centripetal force and the ball will fall out of the jar. In the case of Newton’s First Law, gravity is the force acting on the ball that will stop its motion.
I hope you enjoyed the experiment. Here are some printable instructions: