Opening Jars

When I was visiting my aunt in Minnesota, my younger counsins wanted nutella sandwiches for breakfast. To open the jar of nutella, my aunt used a jar opener much like the one featured here (I didn't have my camera at the time). I instantly connected this with the concept of torque. In order to open the jar, she needed to exert a torque, or force causing rotation, on the lid. Her torque was insufficient to open the lid without the help of the jar opener. How did the jar opener open the lid if the amount of force my aunt exerted was the same? It increased the lever arm, or distance from the axis. Increasing the distance is the only other way to increase torque other than increasing force.

My friend Wathsala, for no apparent rational reason, decided to go sky-diving. Why anyone would do something as counterintuitive as jumping out of a moving air plane hundreds of feets above the ground I can't explain but I can explain the multiple forces acting upon Wathsala as she falls. First and most obviously is gravity, as Newton's Third Law indicated, as the Earth pulls Wathsala down, Wathsala pulls the Earth up with equal force but due to extreme differences in mass, their respective accelerations are varied. Ideally as Wathsala falls she is accelerating at a rate of 9.8 meters per second per second. However, because of air resistance, her acceleration is actually decreasing as she reaches her terminal velocity. Terminal velocity is when air resistance is equivalent to force of gravity. If Wathsala were allowed to fall in an infinite space she'd reach terminal velocity. Unfortunately, there is a finite amount of space between the place where she jumped and the ground and so a parachute was needed to increase the air resistance enough so that it was safe to land.