Density of Helium
A helium-filled balloon moves upwards because the density of the helium gas is less than density of air.
Apparatus
Some irregular solids, 0-500 ml measuring cylinder, top-pan balance is required to perform this experiment.
Measure the mass of the solid object (rectangular blocks) using a top-pan balance.
When the object is first released from a certain height, under the effect of gravity, the only force acting upon it is its own weight. It accelerates downwards with acceleration due to gravity.