Whydo things sink or float? The Tub Sub will let you figure it out for yourself!
As a boat, it floats.
As a sub, it sinks.
For a floating boat, push the flexible blue piece down. For a sinking sub, pull the blue part up and fill the bottom with water. Only the periscope (also a handle) will stay above the water!
Encourage thinking and reasoning with this wonderfully fun and creative toy!