Density -- the amount of matter in a unit of volume.
Weight density -- the amount of weight in a unit of volume.
Elasticity -- the property of a material by which it changes shape when a deforming force acts on it and returns to its original shape when the force is removed.
Hooke's law -- the amount that an object compresses or stretches is directly proportional to the axial force applied to it due to the elasticity of the material.
Fluid -- a material that flows - either a gas or a liquid.
Pressure -- the ratio of the force to the area over which that force is distributed.
Buoyant force -- the net upward force that a fluid exerts on an immersed object.
Archimedes' principle -- an immersed body is buoyed up by a force equal to the weight of the fluid it displaces.
Principle of flotation -- a floating object displaces a weight of fluid equal to its own weight.
Pascal's principle -- the pressure applied to a motionless fluid confined in a container is transmitted undiminished throughout the fluid.
Surface tension -- the tendency of the surface of a liquid to contract in area and thus to behave like a stretched elastic membrane.
Capillarity -- the rise of a liquid in a fine, hollow tube or in a narrow space.
Atmospheric pressure -- the pressure exerted against bodies immersed in the atmosphere. It results from the weight of air pressing down from above. At sea level, it is 101 kPa.
Barometer -- a device that measures atmospheric pressure.
Bernoulli's principle -- where the speed of a fluid increases, the internal pressure in the fluid decreases.
Plasma -- an electrified gas that contains ions and free electrons. Most of the matter in the universe is in this phase.