Why do Boats Float? (Buoyoncy for Kids)

Thursday, June 14, 2018

Why do Boats Float? (Buoyoncy for Kids)

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After you've learned about density for kids including what mass and volume are and why they are needed to find an objects density you are ready to explore this weeks lesson on why boats float.

Boats for Kids

Now that we understand the principles of why boats floatlet's take a peak at the history of boats. Start by reading:

Why do Boats Float

Start off by taking a blob of clay and dropping it into a bin of water. What happens? It sinks - it has a high density.

Now take another lump of clay that is the same weight and make a boat from it. What happens when you put it on the water? It floats because the boats shape makes it have less density. NOTE: I suggest letting the clay boat dry first.

Boats & Cargo

Now using your clay boat (or a plastic lid) try putting pennies in the boat. Keep adding coins (CARGO) until the boat float.

Why did the boat sink?

You increased the mass (weight) without increasing the volume (size). So now try making a longer or wider boat (increasing the volume) and put the same number of pennies on the boat. Did it float now?

HINT: You can build your boat out of aluminum foil too)

For this experiment you will need an ice cube tray. Each compartment is a bulkhead on a ship - which means a compartment of air.  Now when the Titanic hit an iceburg water started entering the front 2 bulkheads.

Have kids place the ice cube tray in water and fill the front 2 compartments. What happened?

As the tray is filled with water it tilts more, the more water fills more bulkeads and it tilts even more. The extra water makes the ship have more mass and thus a higher density. So eventually, when enough water got in, the ship no longer floated.

Submarine Experiment for Kids

You can help kids understand how submarines use air and water ti give and surface.
Supplies Needed:

• 20 oz soda bottle
• scissors
• waterproof tape
• 8 quarters
• flexible straw
• modeling clay
• long plastic tube
First cut three holes in the side of a bottle and one in the cap. Then tape four quarters to the bottom of the bottle at either end.

Place the short end of the straw in the cap of the bottle and use clay to hold it in place. Attach the other end, pointing up, to the plastic tube.

Now place the bottle in the water, making sure to hold the plastic tube above the water. As the bottle fills with water it will get heavier and sink. (in a real submarine the whole ship doesn't fill with water, just the ballast tanks)

Now to submerge your submarine blow hard into the plastic tube. Your submarine will rise to the surface as the air is pushing the water out of the bottle. Now your submarine is less dense than the water so it will float on the surface.

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