A house may feel cool to a person sitting and watching television, but uncomfortably warm to the same person after playing hard outdoors, without the actual indoor temperature changing at all. Having lived through many experiences with forms of heat, students will have plenty of ideas to contribute to this topic. To a scientist, heat is a measure of molecular movement. Even materials that we say are cold, such as ice, have heat. At 90 degrees, water has more heat energy than it has at 50 degrees.
All temperatures are measures of heat energy.
If the metal lid of a jar is heated, like other substances, it expands. We use this principle when we run hot water over a tight jar lid. When heated, the metal lid expands more rapidly than does the glass, making it easier to remove the ring. Some doors will stick during the heat of the day, but work freely in the cool of the night because of the expansion and contraction of materials with changes in temperature. Water behaves strangely as temperatures drop near the freezing point.