- 1). Use a knife and cut 3 inches off the end of the straw. The 3-inch piece of straw is the submarine.
- 2). Put a small lump of sticky tack or reusable putty over each end of the straw so the holes are covered. Drop the straw into a glass of water. The straw sinks if you’ve put enough putty over the ends. If it doesn’t sink, add a little more putty so the straw sinks.
- 3). Remove the straw from the glass and remove a tiny piece of putty from each end then put the straw back into the glass. You need to get the weight correct, so when you drop the straw into the glass it initially sinks a little, and then floats back to the surface. Keep removing small amounts of putty until this happens and then remove the straw from the glass.
- 4). Use tap water and fill an empty clear plastic soda bottle so the level of water is nearly to the neck of the bottle. Drop the straw into the bottle. Add more tap water, so the bottle is full and then put on the bottle top and tighten. You see the straw sub floating near the top of the bottle.
- 5). Make the straw sub sink by squeezing the bottle using your hand. You will see the sub start to sink, and if you squeeze the bottle harder, the sub will sink deeper.
- 6). Start to release the pressure slowly, and you see the sub rising to the surface again. The action of squeezing the bottle increases the air pressure inside the straw sub and replicates a real submarine. Compressed air takes up less space, so the sub gets heavier and sinks. As soon as the pressure is released, the air takes up more space making the straw sub more buoyant, so it floats.
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