If the glass is thin, by the time in inside surface has started to expand appreciably heat has flowed to the outside allowing it to also expand. After water cools below 4 C it becomes less dense, which means it will rise to the top of the body of water. From a statistical point of view having all the molecules of a gas with the same speed would be very unlikely. Though the molecules of the gas are identical, the continual collisions occurring within the gas leads to any particular molecule being sometimes less energetic and other times more energetic than the average. No, one only sees a rise in Hg due to the glass not expanding at much as Hg.
Temperature is a measure of average molecular kinetic energy.
The pressure increases due to the increased velocity of the molecules within the gas. The second is that an increase in speed leads to there being more frequent collisions with the wall of the container. A watermelon will stay cooler longer because it has greater water content than the sandwich and water has a high specific heat. The sand heats up rapidly and thus has a low specific heat. After the ring is placed on the cylinder the ring contracts as it cools down and the cylinder expands as it heats up.