Physics students study a piano being pulled across a room on a rug. They know that when it is at rest, it experiences a gravitational force of 2200 N. When it is being pulled with 1200 N it is sliding across the room in equilibrium, but the students feel like they had to pull harder than 1200 N at first to begin motion.

Adiver named jacques observes a bubble of air rising from the bottom of a lake (where the absolute pressure is 3.50 atm) to the surface (where the pressure is 1.00 atm). the temperature at the bottom is 4.00 ∘c, and the temperature at the surface is 23.0 ∘c.what is the ratio of the volume of the bubble as it reaches the surface (vs) to its volume at the bottom (vb)? if jaques were to hold his breath the air in his lungs would be kept at a constant temperature. would it be safe for jacques to hold his breath while ascending from the bottom of the lake to the surface?