It is a demonstration of the ‘Moment of Inertia’.

The mass itself and the distance of the mass from the centre of the cylinder determines how quickly it will accelerate. The effect can be called also “Angular Momentum”.

The cylinder with the mass concentrated towards the centre rolls faster.  Because of the different distribution of the mass, these rollers of identical size and identical total mass behave very differently when rolled down a slope. The cylinder with the mass concentrated towards the outside accelerates much more slowly because the same magnitude of mass must travel a greater distance around the curve of the cylinder. 
Dimensions: 45 x 56mm (dia. x length) – 400gm. 

Instruction Sheet

Warning: Do not drop cylinders.