Put your cannons and history books away, this Wonder of the Day isn’t about that old black metal piece of ammunition. Instead, we’re taking a closer look at a signature move you’ll see at pools all over the country during the summer.

Playtime at the pool is a summer tradition. When the temperatures climb and the streets feel like ovens to bare feet, millions of families head to a local pool or lake to cool down in the water.

Of course, one of the most fun features of a pool or a lake is the diving board. Who doesn’t love to use a diving board to launch themselves toward the sky, only to — kersploosh! — land in the water with a huge splash?

For who-knows-how-many years, one of the favorite dives of children and even some adults has been the cannonball. Go to any pool or lake with a diving board, and you’ll most likely find a group of children trying to impress each other with their cannonball techniques and the size of their splashes.

To do a cannonball, just jump out from a diving board (or even the side of a pool) as high as possible. While you’re in the air, bring your knees as close as you can to your chest.

Grab and hold onto your knees with both arms, like you’re hugging them. Tuck your chin and plunge into the water like a cannonball.

The goal is to hit the water with your body shaped as much like a sphere as possible. The more like a cannonball you are, the bigger your splash will be.

If you’ve ever wondered why cannonballs make such big splashes, physics holds the answer. When your body shaped like a cannonball hits the water, it displaces a lot of water very quickly. As you plunge into the water, your body’s moving force pushes the water away from it in all directions.

As you sink below the surface, your body makes an air cavity in the water. The cavity is about the size of the object (you) entering the water. Almost as soon as the cavity forms, pressure from the surrounding water causes the cavity to collapse inward. All of this happens in the blink of an eye.

As water continues to rush in to fill the cavity, some of it is pushed upward as the cavity is quickly filled. This is the huge splash that you see after a really good cannonball!

Scientists say that the keys to big splashes are the size of the object, the weight of the object and the speed of impact. You can’t do anything about your size, so focus on perfecting your form if you want to be the best cannonballer at the pool this summer.

The higher you jump before hitting the water, the faster you’ll be traveling when you hit the water. The tighter ball you form with your body, the more like a sphere you’ll be when you go kersploosh! As always, practice makes perfect, so get out there and get your splash on!


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    • Thanks for letting us know you thought the video for this Wonder was AWESOME, Julie! We think YOU are AWESOME for visiting Wonderopolis today and leaving us a comment (and we like your animated smiley face, too)! :-)

  1. To make the animated smiley face i put in my comment, you put a
    colon. Then with no spaces,spell lol(lowercase)
    Last but not least,put the colon on. When you postested the comment, you have a animated smiley :lol:

    • Hey David, cannonballs are lots of fun to do in a deep pool! What a splash they create! We hope you will give the dive another try, perhaps with the help of a lifeguard! :)

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Have you ever wondered…

  • What is a cannonball?
  • How do you do a cannonball?
  • Why does a cannonball make such a big splash?

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Try It Out

Ready to get wet? When the sun is out and the heat is on, there’s no better way to cool down and have fantastic fun with your friends than to head to the local pool or play water games in the backyard.

If you go swimming at a local pool or lake with your friends, take turns doing cannonballs! Who can get the biggest splash? What other dives can you make up?

If you can’t make it to the pool, head out to the backyard and grab the hose. Try some of these splash-tastic games:


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