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Science Boonies: Lil' Silver Submarines


Did You Know?

Did you know that submarines use something called "sonar" to help drive it? If you think about it, since submarines are in the water, you can't see things that are far away very well. So they use sonar to figure out what path they need to take. Sonar is just a fancy word for sound waves. When we talk (out loud) we emit 'sound waves'. We can't see them but trust me, babies, they're there! These sound waves hit the objects around them and then bounce back (kind of like a boomerang). We can use science and math to calculate how far those objects are based off how long it takes for the sound waves to come back to us! With that, the submarine can tell us how far away obstacles are so we don't accidentally smoosh them. Sonar helps keep us and the fish safe!

Today, we're going to make our own submarine and figure out what things we have around the house that will sink or float! The first thing you need to do is read through this whole experiment! It's important that you read through it all and make sure you understand so you don't get lost in the sauce (confused)!



  • Tinfoil

  • 5 - 10 small objects you want to test

  • A basin or bathtub

  • A large cup

  • Table salt

  • Water

  • Coins


Step One - get your tinfoil and try to form it into the shape of a ship. Remember babies, the larger the flat part (the deck) is, the more stable the boat will be. If you make the walls super big, that can make the boat unstable so be careful!

Step Two - put your boat in the water. Does it sink? Does it float? What do you think are some reasons the boat might sink? Now try adding coins (one at a time) to your boat until it sinks! How many coins did it hold?

Step Three - get your testing objects and place them in the water, one by one. What sinks and what floats?

Step Four - for the objects that sink, fill a cup up with water and put your sinking object in it. If you add a tablespoon of salt, does your object now float? Try this with all of your objects that sank. If they didn't float, try adding more salt! Eventually, they should float (unless they're super heavy or dense).

Big Boon Brain Explanation:

What in the world could the salt be doing to make the objects that used to sink, float?! When we add salt to the water, we increase the waters 'density'. Density is just a mathematical way of describing how much air is in something. If an object has a lot of air (like a sponge) we say it has a low density. If an object has very little air (like a rock), we say it has a high density.

Now, babies, I hear you! You're confused 'if we increase the density of the water, how exactly does that help us make stuff float?' great question! Let's say I placed a pebble in the water and sank. The reason it sank was that the rock was more dense than the water. This should make sense - if you place a ping pong ball in the water it will float. Why? Because the inside is completely air. The reason floaties float is they're like 90% air! So if we increase the density of the water by adding salt, then there's a chance that the water will now be more dense than the object. The more salt we add the closer the object should be to floating!

Here's a diagram to help explain - note: this is fancy middle stuff here but any curious littles can feel free to read it as well :)

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