How does the buoyant force affect a submerged object?
Buoyancy acts against the force of gravity, so it acts to make the object rise. If the force of buoyancy is greater than the force of gravity, then the object floats. If it is less than the force of gravity, then the object sinks. Buoyancy is caused by the change in density of the material displaced by the object (this is why ships list their displacement in tons of water). For example, I am 2 m tall, about 0.5 m in circumference, and mass 75 kg. Thus, I displace a volume of 0.5*0.5*pi*2= 1.57 cubic meters. On dry land, that means I displace 1.57 m^3 of air. If air has a density of 1 kg/m^3, then the total force acting on me on land is equal to gravity less buoyancy or 75 kg*9.8 m/s^2 – 1.57 kg*9.8 m/s^2 = 719 N. In the water, I still displace 1.57 m^3 but it now has a mass of 157 kg so the total force acting on me is now 75 kg*9.8 m/s^2 – 157 kg*9.8 m/s^2 = -803.6 N. Because the total force is negative, that means that I rise to the top of the water – I float!
