P11 - Pressure Flashcards
What is fluid pressure
Where the particles in a fluid collide with their container exerting a force which acts at right angles to the surface of the container.
EQuation for pressure
- ρ = F/A
- Pressure (Pa) = Force (N) / area (m²)
Eqaution for pressure of a column of liquid
P = hρg
Why does atmospheric pressure decrease with increasing altitude
- Air molecules colliding with a surface create atmospheric pressure
- At increasing altitude, there are fewer molecules in air above a surface
- This means the weight ofthe air particles above a surface is less than there is at a lower height so the pressure decreases
Why does the pressure of a liquid increase with depth
- More liquid particles above a surface
- This means there is a greater weight (force) acting downwards onto the surface
How does the density of an object determine if it sinks or floats
- If the density of the object is less than the density of the liquid, it floats
- If the densities are the same, the object is suspended
- If the density of the object is more than the density of the liquid, it sinks
Relationship between the size of the upthrust and weight of the fluid
The size of the upthrust acting on an object is the same as the weight of the fluid dispalced by the object
What is upthrust
Where a submerged object experiences an upwards rsultant force due to the pressure on its lower surface being higher than the pressure on its upper surface
Explain how snowshoes work
- Snowshoes have a larger surface area than a person’s trainers
- As the weight (force acting downwards) stays the same but the area increases, the pressure decreases as p = F/A
- This means the person is less likey to sink into the snow
How does the upthrust and weight determine if an object sinks or floats
- If the upthrust is equal to the weight of the object, the object will float
- If the weight of the object is greater upthrust, the object will sink
average pressure at sea level
100kPa
relationship between pressure and volume
pV = constant
