Buoyancy

Buoyancy is kind of like when you fill up a big balloon with air and it makes it look bigger and floaty. That's what buoyancy does too. It's like a magic force that objects have that can make them lighter and float in water or in the air. When an object is less dense than the water or the air around it, buoyancy helps it float. When an object is more dense than the water and air around it, buoyancy pushes it down. That's how boats can float, and how submarines can go underwater.