The warm water heats the bottle which, in turn, heats the air inside the bottle after the water is poured out. When the bottle is placed in the cold water, the air inside cools and contracts, causing outside air to be drawn in, pulling the balloon in and inflating it inside the bottle. All objects have a center of gravity that acts as if all the weight of the object were balanced there. The center of gravity of the ruler is in the middle, but the hammer moves the center of gravity of the system to under the table's edge which keeps it from falling. The rice gets more and more packed down by repeated stabs from the knife until the rice is so compact that it presses against the blade of the knife with enough force to overcome the pull of gravity on the jar.
Surface tension prevents the water from seeping through the handkerchief.
The higher air pressure outside the glass forces air to penetrate the handkerchief and bubble through the water. We encourage duplication for educational non-commercial use. Educational materials developed with the National Science Teachers Association.