Force and Pressure
Pressure - the force per unit area.
Density - measure of the 'compactness' of a substance, how close together the particles.
Upthrust - a resultant force upwards caused by when a force exerted on the bottom of an object is larger than the force acting on the top of the object.
Floating object - the upthrust is equal to the object's weight.
Sinking object - the weight is larger than the upthrust.
Atmospheric pressure - created on a surface by air molecules colliding with the surface.
Altitude - height above Earth.