Uncle Tony’s cool science experiment

related to My Imaginary Week.

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Items you will need:

1. table salt
2. 8-ounce, plastic glass
3. permanent marker
4. spoons for stirring and measuring
5. liquids measuring cup
6. 8 small marbles
7. miniature marshmallows
8. blueberries the same size as the marbles & marshmallows
9. tapwater

When Annabelle & Andrew sailed with their family, Annabelle secretly worried that Uncle Tony’s boat would sink when they boarded with their tummies full of a big dinner. Maybe we’re too heavy for this little sailboat, now, she thought. Later, Uncle Tony showed them an experiment about buoyancy & density.

You may already know that objects fall to the ground when the force of gravity pulls them down. You may also have noticed that certain things float on top of water, but other things (like your body) may sink! That is why it is very important to learn how to swim!

But, do you know why some very heavy boats don’t sink?

The answer is that gravity is not the only force working on the boat. The force of buoyancy pushes up from the water while gravity pulls down. Which force will win? It depends upon the density of the boat (and its cargo) compared to the density of the water on which the boat rests.

Annabelle and Andrew learn a lot about balance in My IMAGINARY Week. This is another kind of balance. Here is how you can try Uncle Tony’s experiment with an adult:

1. Assemble the items in the list and picture above.
2. Using warm water from a faucet, fill a liquid measuring cup to the 4-ounce mark.
3. Pour that water into a clear, 8-ounce, plastic glass.
4. Mark the water line (near halfway up) with a permanent marker and label it #1.
5. Slowly add the 8 small marbles to the glass.
6. Mark the new water line and label it #2.
7. Carefully remove the marbles. Check to make sure the water level has returned to #1. If you have accidentally removed some water with the marbles, add a few drops to bring the water back up to the original level.
8. Add blueberries into the glass until the water rises to mark #2. When Annabelle & Andrew did this, it took 8 blueberries for the water to rise to the same mark. That meant that the density of the blueberries (like the density of the marbles) was more than the density of the water. Even though they were softer than the marbles, the berries contained moisture that added to their weight. Both the marbles and the blueberries were heavier than the water, so they dropped to the bottom of the glass.
9. Carefully remove the blueberries and check the water level, again. See how many marshmallows are needed to bring the water level up to the #2 mark. When Annabelle & Andrew did this, it took 13 marshmallows. Their marshmallows puffed up and floated on top of the water because the denser water pushed them up with the force of buoyancy. The density of the marshmallows was better balanced with the density of the water, so they floated like Uncle Tony’s boat.
10. Now you can make the water denser with salt — like the water in the ocean. Start with 4 ounces of warm water in the measuring cup.
11. Add one teaspoon of table salt. Stir. Pour just enough into the plastic glass to reach the #1 mark.
12. Repeat the steps of the first experiment .
13. When Annabelle & Andrew did this, they found that the marbles acted the same because they were denser than the saltwater. Then, 6 of their blueberries floated because those berries were balanced with the water and slightly less dense the other berries (7 berries sank to the bottom of the glass). Thirteen of Annabelle & Andrew’s marshmallows floated to the top at the #2 mark, as before, because they were still balanced with the water.

Uncle Tony explained why, when you put marbles into his boat, the boat will float. It is because the boat covers a large area of water and the boat contains a lot of light air. The big, air-filled boat acts like the marshmallows; it spreads its weight across a big amount (volume) of water, so the weight of all that water underneath is more than the weight of the boat and its cargo. The big amount of water pushes up the boat with the force of buoyancy, even though the force of gravity is pulling down at the same time. Unless a boat is too heavy for its size, the force of buoyancy wins. If Uncle Tony had piled in all the people he knew, his boat probably would have sunk and they would have had to swim to shore!

(Of course, without the force of gravity, the boat would float up into the air!)

Now that you have worked hard on this experiment, you may eat any leftover blueberries and marshmallows!

Coming soon:

Grandma Merriday’s shell craft.