How to Make Cartesian Bottle Diver?

You may see some sea creatures give off the water when they swim on the surface of the water. Do you know why?  This science experiment Cartesian Bottle Diver will tell you why. Kids are always having fun with this toy.

Age: 5+         Time: < 10 mins

 Safety 

1. Adult supervision.
2. Take care, children may swallow small parts.

 Materials List 

• Water
• Transparent plastic bottle (mineral water bottles, cola bottles, etc.)
• Drinking straws (juice straws, cola straws, etc.)
• Paper clips
• Scissors

 Instruction 

Step 1/3 – Cut out a piece of drinking straw about 5cm (It can be longer. The longer the drinking straw, the more paper clips are required), fold the straw in half, secure both ends with a paper clip. Not to seal both ends of the drinking straw.

Step 2/3 – Place it in the water and see if it can barely float on the water. When it is given a small push from the top, it falls down in the water, and then comes back, floating on the water again. If it dives directly into water and never comes back again, you need to make the drinking straw longer. If it floats on water too high, you need to make a shorter straw or add more paper clips. Whatever, make the diver barely float.

Step 3/3 – Fill a transparent bottle with water to the very top. Put the Cartesian Diver into the bottle and close the lid firmly if you don't want to the lid pop out when you squeeze the bottle. When you squeeze the bottle the Cartesian Diver will dive to the bottom.  It will rise up when you release the squeeze.

  

 Troubleshooting 

Why my Cartesian diver cannot dive into the water when I squeeze the bottle?
— Check if you have done Step 2/3 right. Put more paper clips on the diver or cut the straw shorter.

Why when I put back the lid the Cartesian Diver will directly dive into the water and never come back?

— If you secure the straw in the right way?

— If you put the diver in the water in the right way?

— Reduce some paper clips or cut a longer straw. 

Why does the Cartesian Diver sink to the bottom after playing for a while?
— It is some water that takes up the room where the air stays in the straw. Take out the diver, empty the water in the dropper, and put it back.

 Question to Ask 

1. Why can Cartesian Diver float on the surface?
2. Why when you a force is put on the bottle the Cartesian Diver goes down?
3. In addition to using a straw, what else do you think can make a Cartesian Diver?

 Scientific Description 

The Cartesian Diver is balanced by the buoyancy of the water in the water and the gravity. Archimedes' principle states that the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially submerged, is equal to the weight of the fluid that the body displaces and acts in the upward direction at the center of mass of the displaced fluid. When the Cartesian Diver is placed in the water at first, its buoyancy is almost equal to gravity, just slightly larger than gravity, so the Cartesian Diver can just float on the water. When the bottle is forced hard, the pressure of the water is increased, and the air in the drinking straw is compressed, in another word, the volume of the drinking straw becoming smaller so that the buoyancy of the Cartesian Diver is reduced. The gravity of the Cartesian Diver is greater than that of its buoyancy. The Diver will sink. When the force is released, the pressure of the water returns to its original state, and the buoyancy of the Cartesian Diver also returns, so the Cartesian Diver will rise back.

Cartesian diver and a submarine work in similar ways. When the

submarine wants to go down into the water, it takes water into tanks until the submarine sink. This happens because the water in the tanks increases the density of the submarine to make it sink. When the vessel wants to go to the water surface, lots of air is blown into its tanks, the water is forced out, so the submarine becomes less dense and ascends to the surface. 

 Extensions 

1. You can replace the drinking straw and paper clips unit with a droppers and paper clips unit. Anything that can load some air in the water and suspend in water will be the material for this Cartesian Diver experiment.
2. You can make the Cartesian diver into a marine creature to create a sea world inside the bottle.

 Disposal 

The material is recyclable.

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