Fighter jets are used primarily in air defense to engage enemy aircraft in aerial combat and to protect airspace from threats.

Air defense systems are designed to detect, track, and intercept incoming missiles or aircraft to protect airspace from threats.

Rockets typically use liquid hydrogen and liquid oxygen as fuel, as they provide a high-energy output necessary for propulsion into space.

Aeroplanes use Bernoulli's principle, which states that faster-moving air creates lower pressure, helping to lift the plane when air moves faster over the curved top surface of the wing.

Warm water in river generally gets denser when it becomes colder, and therefore sinks. This fact may make you believe that ice should form on the bottom of a lake first. But a reverse happens to water as it gets even colder. When colder than 4° Celsius (39° Fahrenheit), water begins expanding and becomes less dense. As a result, close to freezing, colder water floats to the top and the warmer water sinks to the bottom. As a result, the coldest water floating to the top of the river in winter, freezes to form a layer of ice.

The force exerted upon the earth by air is called pressure. The typical pressure at sea level is 76 cm of Hg or 1013.25 millibars or 14.7 pounds per square inch.

The process in which water change into its solid state at a constant temperature by releasing heat is called ice. In ice the water molecules become slow down enough that their attractions arrange them into fixed positions. Water molecules freeze in a hexagonal pattern and the molecules are further apart than they were in liquid water. Therefore, a fixed amount of water gains volume than its liquid state but, weight will remain the same.

The boiling point of water is 212 degrees Fahrenheit or 100 degrees Celsius under standard pressure at sea level. That means in most places this is the temperatures of boiled water.

Under the ideal condition, the freezing point of pure water is 0 degrees Celsius, or 0 degrees centigrade.

In ideal environment water's density is greatest at about 4 °C (39.2 °F) in the liquid phase.