Pressure & Pressure Differences in Fluids (Edexcel GCSE Physics): Flashcards
Exam code: 1PH0
1/340Still learning
Know0
- FrontPressure in Fluids
Define fluid.
Was this flashcard helpful?
Cards in this collection (34)
Define fluid.
A fluid is either a liquid or a gas.
Define atmospheric pressure.
Atmospheric pressure is the pressure exerted by the Earth's atmosphere, caused by air molecules colliding with a surface.
An object at sea level experiences an atmospheric pressure of 101 kPa. If it is submerged to a depth of 10 m in water, where the water exerts an additional 100 kPa, what is the total pressure on the object?
101 kPa + 100 kPa = 201 kPa. The total pressure is the sum of the atmospheric pressure and the liquid pressure.
In what direction do the forces created by fluid pressure act on a surface?
At 90 degrees (normal) to the surface.
Atmospheric pressure is about ______ kPa at sea level.
Atmospheric pressure is about 101 kPa at sea level.
Why does atmospheric pressure decrease with increasing altitude?
The atmosphere becomes less dense with height, so there are fewer air molecules (and less weight of air) above a surface, reducing the pressure.
True or False?
Atmospheric pressure is the same at all altitudes.
False.
Atmospheric pressure decreases with increasing altitude, because the atmosphere becomes less dense with height.
Define pressure.
Pressure is the concentration of a force, or the force per unit area.
Why do tractors have large tyres?
Large tyres spread the tractor's weight (force) over a large area, reducing the pressure and preventing the tractor from sinking into mud.
Why can a nail be hammered into a wall?
Its sharp point has a very small area, which concentrates the force to create a large pressure.
Pressure is calculated using the equation pressure = force ÷ ______.
Pressure is calculated using the equation pressure = force ÷ area.
What is the unit of pressure?
Pascals (Pa).
Which area should be used when calculating pressure from a force?
The cross-sectional area — the area at right angles (normal) to the force.
True or False?
The pressure produced by a force does not depend on the area over which it is applied.
False.
Pressure depends on both the force and the area — spreading a force over a larger area reduces the pressure.
How does the pressure in a liquid change with depth?
Pressure increases with depth — the greater the depth, the greater the pressure.
How does the density of a liquid affect the pressure it exerts at a given depth?
A denser liquid exerts a greater pressure at the same depth.
Why does pressure in a liquid increase with depth?
Pressure is caused by the weight of the liquid above a point. Further down, there is more liquid (and so more weight) pushing down, increasing the pressure.
The pressure on the seabed is far ______ than the pressure at the surface of the ocean.
The pressure on the seabed is far higher than the pressure at the surface of the ocean.
A column of water has a hole at the top and a hole at the bottom. Which hole produces the more forceful jet of water, and why?
The bottom hole, because the pressure (and so force) is greater at the bottom due to the greater weight of water above it.
True or False?
The pressure exerted by a liquid on an immersed object acts only downwards.
False.
The pressure is exerted evenly across the whole surface and in all directions.
Write the equation used to calculate the pressure due to a column of liquid.
p = hρg
In the equation p = hρg, h represents the ______ of the column of liquid, measured in metres.
In the equation p = hρg, h represents the height of the column of liquid, measured in metres.
What are the units of p, h, ρ and g in the equation p = hρg?
p in pascals (Pa), h in metres (m), ρ in kilograms per metre cubed (kg/m³), g in newtons per kilogram (N/kg).
In what directions is the force from a liquid's pressure exerted on a submerged object?
Evenly, across the whole surface and in all directions.
Calculate the depth of water in a pool that exerts a pressure of 20 kPa. The density of water is 1000 kg/m³ and g = 9.8 N/kg.
h = p ÷ (ρg) = 20 000 ÷ (1000 × 9.8) = 2.04 m.
True or False?
The pressure in a liquid is the same at every depth.
False.
Pressure increases with depth, so the pressure at different depths in a liquid is different.
Define upthrust.
Upthrust is the upward force exerted on an object submerged in a fluid, acting in the opposite direction to the object's weight.
What causes upthrust on a submerged object?
The difference in pressure between the top and bottom of the object. Since pressure increases with depth, the pressure on the bottom surface is greater than on the top surface.
What two factors determine the size of the upthrust on an object?
The density of the fluid and the volume of fluid displaced (equal to the volume of the object).
What is upthrust equal to?
The weight of the fluid displaced by the object.
An object will float if the upthrust acting on it is ______ to or greater than its weight.
An object will float if the upthrust acting on it is equal to or greater than its weight.
A cube of side 40 cm is submerged to a depth of 20 cm in water (density 1 g/cm³, g = 10 N/kg). Calculate the upthrust on the cube.
Submerged volume = 40 × 40 × 20 = 32 000 cm³. Mass of displaced water = 32 000 g = 32 kg. Weight = 32 × 10 = 320 N, so the upthrust is 320 N.
Why does an iron block sink in water while a polystyrene block floats?
Iron is much denser than water, so it sinks. Polystyrene is much less dense than water, so it floats.
True or False?
An object will float if its density is greater than the density of the fluid it is placed in.
False.
It will sink. An object floats if its density is less than the density of the fluid.
Sign up to unlock flashcards
or