Thyroid hormone tells all of the cells in your body how busy they should be. Too much thyroid hormone (hypERthyroidism), and your body goes into overdrive; not enough thyroid hormone (hypOthyroidism), and your body slows down.
Place the pot on the stove and turn the heat to high. Check for steam escaping from under the lid, then lift the lid carefully to see how the water is doing. Look at the water. If large bubbles are rising from the bottom of the pot to the surface, the water is boiling.
Boiling occurs when the vapor pressure reaches or exceeds the surrounding pressure from the atmosphere or whatever else is in contact with the liquid. At standard atmospheric pressure (1 atmosphere = 0.101325 MPa), water boils at approximately 100 degrees Celsius. That is simply another way of saying that the vapor pressure of water at that temperature is 1 atmosphere. At higher pressures (such as the pressure generated in a pressure cooker), the temperature must be higher before the vapor pressure reaches the surrounding pressure, so water under pressure boils at a higher temperature.