This is a kit for demonstrating Archimedes' principle and comprises a tub having an overflow spout, such that when a fluid level reaches the overflow spout, all additional fluid added to the tub will flow out of the overflow spout; and a stable boat sized to float in the tub without touching the sides of the tub. The kit may further comprise a balance beam which can balance on an edge of the tub, wherein one end of the balance beam has an attachment mechanism for attaching a counter weight, and the other end has an attachment mechanism for attaching a sample weight such that when the sample weight attached to this end, and the balance beam is balancing on the too edge of the tub, the sample weight will be submerged in the fluid in the tub. There is also provided a method for using this kit to demonstrate Archimedes' principle both for the buoyancy of a floating body, and the buoyancy for objects that do not float.