This Wednesday was the East Oahu Robotics Tournament. It was a lot of fun and the day was filled with physics. The competition was in the Iolani Lower Gym, so afterward we stayed to help clean up. Our task was to roll up the floor coverings and put them into a box located by the door. It turns out that those mats are pretty heavy and take at least two people to lift one.
The mat has a weight (mass times gravity) directed downward and when it is on the ground, a normal force pointing upwards that is equal (but opposite) to the weight. In order for a person (or two
) to lift this mat they have to apply a force that is greater than the weight, thus resulting in an upward acceleration of the mat. This is shown in Newton's second law, F=ma (force =mass times acceleration.
However, once the mat is in the air a force equal and opposite to the weight must be applied to keep the mat stationary (F=ma, a=0, when upward and downward forces are equal). Also, though it may seem as though work is being done as the mat is moved to its box, the force is applied perpendicularly to the motion of the mat so no work is being done.
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