Can you make something sink that floats?

Answer 1

Increase its contact surface area and decrease its mass.

Answer 2

Yes. You could add something in it or on it, you could push it down further into water (works with some objects), or you could add weight to it. For example, if you had a boat, it would float in water. But once you push it down or allow water to flow inside of it, it will sink and it will stay sunk.

In short:

Increase the density of the object or reduce the density of the water in which it floats.

For instance, salt water is more dense than fresh water. If you have an object that floats in salt water, and reduce the salinity of the salt water by adding fresh, the object will eventually sink.

Answer 3

Yes !

Just add a good amount salt.

Depending on the size of the object.