What do the terms positive buoyancy, negative buoyancy, and neutral buoyancy mean in relation to sinking and floating?

With i really need the correct answer!

Using a wheel and axle, a farmer is trying to lift a bucket of water from the bottom of a well. the larger wheel has a radius of 40 cm compared to the axle that has a radius of 10 cm. if a bucket of water is 50 n, then how much effort is required to raise it? 12.5 n 200 n 2 n 500 n

Describe uniform velocity and variable velocity in short