How does a meter stick with a balloon on top balance on your finger?

Answer 1

A meter stick with - or without - a balloon on top balances on your finger when the sum of torques around the support point equals zero. When the support is an extended object such as a finger, the meter stick will be balanced when a line drawn toward the center of the planet from the point around which the sum of torques is zero is within the supported zone. Torque results from a force being applied at a distance from the point under consideration. When using a massive object such as a ruler as a backbone for torques, one must consider the mass of the ruler. For the purposes of torque calculations, consider the weight of the ruler to act at the center of gravity of the ruler and to point towards the center of gravity of the object which gives the ruler weight. In most cases that object will be Earth. If one's measurements are very sensitive, one must take into consideration surface features such as near by mountains, latitude and cetera...