Pressure

• What is pressure?

  the effect of a force acting over an area
• How does fluid pressure work?

  As the particles move, they collide with surfaces and other particles, applying a force on the surface when they collide.
• pressure at a point in a liquid depends on...

  depth and density
• What is upthrust?

  when an object is submerged in a fluid, pressure will be exerted on it from every direction.
• Atmospheric pressure decreases as altitude increases because:

  At higher altitude the density of the particles are lower.

  There are fewer particles so this must mean that there are fewer collisions between the particles and the surface.

  As there are fewer particles, there is a lower weight of particles acting downwards. So the pressure has decreased.