Air is all around us, but because we can’t “see” it, we often don’t realize it’s power and how it affects objects. This simple air pressure experiment is fascinating and might leave you scratching your head and wondering how it works, but the good news you won’t have to wonder for long!
In addition to a short demo video of the experiment, below you’ll find everything you need to try it yourself including the science of why it works, other ideas to test the concept, and more simple air pressure experiments to try.
Be sure to hypothesize what you expect to happen to the ping pong balls before you conduct the experiment and let us know if you were right!
- 2 Ping Pong Balls
- String (2 pieces of string each 2+ feet long)
- Drinking Straw
- Stationary Object to hand strings from (i.e. Door Frame, Shower Curtain, Clothes Drying Rack)
Step 1 – Gather two ping pong balls, and cut two pieces of string that is 2 feet in length or longer (length will depend on where you are hanging the string from).
Step 2 – Tape one end of one piece of string to the first ping pong ball. Tape one end of the other piece of string to the second ping pong ball.
Step 3 – Hang the other end of the string to a stationary object. The objective is for the ping pong balls to hang freely in the air at the same level and about 4 inches apart.
Helpful Tip: We used a clothes drying rack. You could also tape them to a door frame or hand them to a shower curtain rod.
Step 4 – Make sure the ping pong balls hang in mid-air at the same height about 4 inches apart.
Now ask a few questions. What do you think will happen if you blow air between the two ping pong balls? Do you think the air will cause them to move? In what direction? Write down your hypothesis (prediction) and then follow the step below.
Step 5 – Use a drinking straw to blow air directly in between the ping pong balls. Position yourself so the straw is level with the ping pong balls and about 4 to 5 inches behind them. What happens to the ping pong balls when you do this?
Now, take a moment to write down your observations. Was your hypothesis correct? Do you know the reason why the ping pong balls moved toward one another? Find out the answer in the how does this experiment work section below.
Air pressure is the secret to this experiment. Air pressure is the pressure caused by the weight of a column of air pushing down on an area. All objects on Earth are constantly being “pushed on” by this column of air. Air pressure can decrease when air is in motion.
When you blow air between the ping pong balls in Step 5, you cause the air between the ping pong balls to move faster, lowering the air pressure between them. The air on the outside of the ping pong balls is relatively still compared to the moving air between the ping pong balls, resulting in high pressure on the outside of the ping pong balls. This high-pressure air on the outside of the ping pong balls moves toward the lower pressure air between the ping pong balls and it pushes the ping pong balls together in the process.
Fluids (like air or water) flow from areas of high pressure to areas of low pressure. According to Bernoulli’s principle, the faster the fluid moves, the less pressure the fluid exerts.
Other Ideas to Try
Try using empty soda cans instead of ping pong balls. Do the soda cans behave in the same way as the ping pong balls?
More Science Fun
If you are looking for more experiments dealing with Air Pressure then you’re in luck. Check out these other fun and simple experiments we’ve done that show the power of air.
- How to crush a plastic bottle
- Use a simple science “trick” to easily stab a regular drinking straw through a raw potato
- Or turn a Water Glass upside down without spilling the water!
- And you can even make a balloon fly across the room like a rocket
I hope you enjoyed the experiment. Here are some printable instructions: