Pressure and Pressure Differences in Fluids - Paper 2

Question 1

Define upthrust

Answer 1

Upthrust is the force due to the pressure difference on the top and bottom surface of a partially or totally submerged object.

Question 2

Why does atmospheric decrease as altitude increases?

Answer 2

• Air molecules colliding with a surface create atmospheric pressure.
• The number of air molecules (and so the weight of air) above a surface decreases as the height of the surface above ground level increases.
• So as height increases there is always less air above a surface than there is at a lower height.
• So atmospheric pressure decreases with an increase in height.