This demo is to show that a block sliding down an inclined plane increases its velocity and acceleration and does not travel at a constant velocity.  Set the angle of the incline so that the block slides easily down the ramp (Waxing the ramp to remove the dust and dirt may be necessary).  Place the motion detector at the top of the ramp on the Velcro strips.  Place the double block system at the top of the ramp and start the interface (The double block is necessary to get a good signal by the motion sensor).  Plots of velocity or acceleration or both are possible.