5.5 Pressure in liquids and gases Flashcards
What is a fluid? (1)
A liquid or gas
What does the pressure in fluids do to any surface? (1)
It causes a force normal (at a right angle) to the surface.
What is the equation to calculate pressure at the surface of a fluid? (1)
Pressure (Pa) = force [normal to a surface] (N) / area (m2)
What is the equation to calculate pressure due to a column of liquid? (1)
Pressure (Pa) = height [of column] (m) x density [of liquid] (kg/m2) x gravitational field strength (N/kg)
How does pressure in liquids at a point increase with depth? (3)
- As depth increases, the mass of liquid above that depth also increases.
- This means the force applied due to the mass increases.
- Since the force increases whilst the area stays the same, the pressure increases.
How does pressure in a liquid at a point increase with density? (3)
- As the density increases, the number of particles in a given volume increases.
- This means the weight of the fluid is greater.
- This means the force above a point has increased, causing the pressure to increase.
Why are objects submerged in a liquid subject to upthrust? (3)
- Partially or completely submerged objects have a greater pressure below it than above it,
- because there is more weight above it at the bottom than at the top,
- leading to an upward force called upthrust.
What factors influences whether you float or sink? (3)
- Weight
- Upthrust
- Density of water
What is upthrust equal to? (1)
The weight of the fluid that the object displaces.
Why can an object with a greater density than water never float? (2)
- There would not be enough volume of water displaced to produce an upthrust larger than the object’s weight.
- This is because upthrust is equal the the water displaced by the object, so it will sink.
What is the Earth’s atmosphere? (1)
A thin (relative to the size of Earth) layer of gas surrounding the Earth.
What is the relation between the atmosphere’s density and altitude? (1)
The higher the altitude, the less dense the atmosphere becomes.
Explain why atmospheric pressure decreases with an increase in height? (4)
- Air particles colliding with a surface creates atmospheric pressure.
- The number of air particles (and weight of air) above surface decreases as the height of a surface above ground level increases.
- So as height increases there is less air above a surface than at a lower height
- So as height increases, atmospheric pressure decreases
