This weeks lab is on work and energy.� Students measure the speed of a mass as it is pulled along a track by a falling mass.� By comparing the kinetic energy of the system� to the work done by gravity on the falling mass they should be able to verify the work energy theorem. � An alternative interpretation is that by summing the kinetic energy and the gravitational potential energy of the falling mass they can show mechanical energy is conserved in this system.
There are two steps the students need to take to ensure their data has no significant influence from friction.� First they need to tilt the track that the sliding mass sits on so that� the mass slides without acceleration (i.e. tilt it down a bit to overcome friction).� Secondly they need to ensure the string that connects the masses touches only the pulley, and not the mechanical stopper at the end of the track.� If the string is routed improperly it will slide along the bottom of the mechanical stopper dissipating energy.��
The measurement of the speed of the falling mass involves the use of a rotation sensor attached to the pulley. To convert between angular velocity and linear velocity students will need to know the radius of the pulley which they can measure using vernier calipers. This slide that is also on transparency in the lab rooms that may be of assistance in explaining how verneir calipers work. There is also an excellent online tutorial through hyperphysics.
Note that the speed measurement using photocells in the video has been replaced with the use of the rotation sensor on the pulley to measure speed