1. Buoyancy: This is the upward force exerted by a fluid (in this case, water) that opposes the weight of the object submerged in it. It's the force that makes you feel lighter in the water.

2. Gravity: This is the downward force that pulls you towards the center of the Earth. It's what keeps you from floating away entirely.

The balance between these two forces determines whether you sink or float. If the buoyant force is greater than the force of gravity, you float. If the force of gravity is greater, you sink.