M-EngMom6: Conservation of Mechanical Energy; example: rollers on inclined planes.

PIRA: Unknown

Equipment: Roller and inclined plane with large groove down center (same as used in M-K7), steeper incline with sandpaper track of similar design, stand rod about two feet long, short stand rod that has been forced into a rubber tube to make a rubber-tired roller. This is located in Set 7, Cabinet 3, Shelf 2.

Procedure: The inclined planes are fitted together at the low ends of each and aligned as shown in the photo. The disc roller is placed against the stops at the top of the long incline and allowed to roll down, up the steep incline, back down the steep incline, and up the shallow incline. Note by a mark the highest position attained on the long incline on the roller's return. Most students are surprised that this position is so near that of the starting point, especially as the disc is so leisurely in its travel.

Repeat, using the stand rod instead of the disc on a shaft. The journey is quick, but the return is not as near the starting point as in the previous experiment. Much of the mechanical energy degradation in the second case is due to windage: a longer rod has more windage and further degrades the mechanical energy of the system.

Repeat again, using the rubber-tired rod. Even more degradation of mechanical energy is noted -- converted to heat in the rubber by plastic deformation. Oftentimes this last run is difficult to make because the rubber-tired roller does not roll straight. However, it is worth a try.