Background information
Explain that buoyancy force is the force a liquid exerts on materials placed in it. This force opposes the weight of the object. An example of this is a beach ball in a pool. It is difficult to push the ball under the water due to the buoyancy force the water is exerting upward on the ball. This force is much greater than the force the ball in exerting downward on the water due to its mass. That is why the ball floats. When the mass of the object on the water increases to where it is exerting a force greater than the buoyancy force of the water, the object sinks. F=m x g. You can also discuss Archimedes principle: The buoyancy force exerted on a body placed in a fluid is equal to the weight of the fluid the body displaces.
For the second part, we will prove objects move when unbalanced forces act on them. Newton’s first law says objects remain at rest or remain moving until an outside force acts upon them. The boats will remain stationary until acted upon by an outside force. This principle will be used to move the boats with a sail and fan, where the fan will be the outside unbalanced force operating on the boat. We will measure how far that force moves the boat and discuss the forces that moved and stopped the motion of the boat.