Density is the mass per unit volume of an object.

Why are gases less dense than liquids and solids?

Gases have fewer particles, and therefore less mass, per unit volume than liquids and solids.

Pressure is the force per unit area .

Is pressure a vector or a scalar quantity?

Pressure is a scalar quantity, so it does not have a specific direction.

Why does the same person exert a greater pressure wearing high-heeled shoes than flat shoes?

The same force (their weight) acts over a much smaller area in a high heel, producing a greater pressure .

If a force is spread over a small area, this will result in a .......... pressure.

If a force is spread over a small area, this will result in a large pressure.

Define hydrostatic pressure .

Hydrostatic pressure is the pressure at a point within a fluid, exerted by the weight of the fluid above that point.

How is the total pressure on an object submerged in a liquid calculated?

Total pressure = hydrostatic pressure + atmospheric pressure

The pressure at the bottom of a fluid is .......... than the pressure at the top, because there is a greater weight of fluid above.

The pressure at the bottom of a fluid is greater than the pressure at the top, because there is a greater weight of fluid above.

True or False? At a given point in a fluid at rest, pressure only acts in the downward direction.

False. In a fluid at rest, all points are in equilibrium , so pressure acts in all directions at each point.

Upthrust (or buoyancy force) is a force which pushes upwards on an object submerged in a fluid .

What causes the force of upthrust on a submerged object?

The difference in hydrostatic pressure between the bottom and top of the object — pressure is greater at the bottom because it is at a greater depth.

Why is upthrust significantly greater in liquids than in gases?

Liquids are much denser than gases, so the hydrostatic pressure difference (and resulting upthrust) is greater.

What condition must be met for an object to float in a fluid?

The object's density must be less than the density of the fluid it is immersed in.

True or False? An object's apparent weight increases when it is immersed in a fluid.

False. Apparent weight decreases , because upthrust acts upwards and partially supports the object's weight.

Upthrust is directly proportional to the .......... difference between the top and bottom of a submerged object.

Upthrust is directly proportional to the pressure difference between the top and bottom of a submerged object.

State Archimedes' Principle .

An object submerged in a fluid at rest experiences an upward upthrust equal to the weight of the fluid displaced by the object.

Under what condition does an object float, according to Archimedes' Principle?

It floats when the magnitude of the upthrust equals the weight of the object.

Explain, using Archimedes' Principle, why ships made of dense materials such as steel are able to float.

A ship's shape means it displaces a volume of water whose weight equals the ship's own weight , so the upthrust balances the weight.

True or False? An object placed in a fluid always sinks until it reaches the bottom.

False. An object sinks only until the weight of the fluid it displaces equals its own weight , at which point it floats.

Since m = ρV , the upthrust force F = mg can also be written as F = .......... , which is the weight of the fluid displaced.

Since m = ρV , the upthrust force F = mg can also be written as F = ρVg , which is the weight of the fluid displaced.

A LevelPhysicsCambridge (CIE)Flashcards4. Forces, Density & PressureDensity & Pressure

Density & Pressure (Cambridge (CIE) A Level Physics): Flashcards

Exam code: 9702

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FrontDensity
Define density.
FrontDensity
What is the equation for density, and what are the units of each quantity?
BackDensity
$ρ = \frac{m}{V}$
ρ = density in kilograms per metre cubed (kg m^-3)
m = mass in kilograms (kg)
V = volume in metres cubed (m³)

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Cards in this collection (29)

Define density.
Density is the mass per unit volume of an object.
What is the equation for density, and what are the units of each quantity?
$ρ = \frac{m}{V}$
- ρ = density in kilograms per metre cubed (kg m^-3)
- m = mass in kilograms (kg)
- V = volume in metres cubed (m³)
Why are gases less dense than liquids and solids?
Gases have fewer particles, and therefore less mass, per unit volume than liquids and solids.
True or False?
The density of an object depends on its mass and its weight.
False.
Density depends on an object's mass and volume ( $ρ = \frac{m}{V}$ ), not its weight.
How can the volume of an object be found if it is not given directly in a question?
The volume can be calculated using the appropriate equation for the object's shape, for example for a cuboid, $V = l w h$ (length × width × height).
Define pressure.
Pressure is the force per unit area.
What is the equation for pressure, and what are the units of each quantity?
$p = \frac{F}{A}$
- p = pressure in pascals (Pa), where 1 Pa = 1 N m^-2
- F = force in newtons (N)
- A = area in metres squared (m²)
Is pressure a vector or a scalar quantity?
Pressure is a scalar quantity, so it does not have a specific direction.
Why does the same person exert a greater pressure wearing high-heeled shoes than flat shoes?
The same force (their weight) acts over a much smaller area in a high heel, producing a greater pressure.
True or False?
The pressure exerted on a surface depends only on the force applied, not on the area it acts over.
False.
Pressure depends on both the force and the area it acts over ( $p = \frac{F}{A}$ ).
If a force is spread over a small area, this will result in a .......... pressure.
If a force is spread over a small area, this will result in a large pressure.
Define hydrostatic pressure.
Hydrostatic pressure is the pressure at a point within a fluid, exerted by the weight of the fluid above that point.
What is the equation for the change in hydrostatic pressure between two points in a fluid?
$Δ p = ρ g Δ h$
- Δp = change in pressure (Pa)
- ρ = density of the fluid (kg m^-3)
- g = gravitational field strength (N kg^-1)
- Δh = change in height (m)
How is the total pressure on an object submerged in a liquid calculated?
Total pressure = hydrostatic pressure + atmospheric pressure
The pressure at the bottom of a fluid is .......... than the pressure at the top, because there is a greater weight of fluid above.
The pressure at the bottom of a fluid is greater than the pressure at the top, because there is a greater weight of fluid above.
True or False?
At a given point in a fluid at rest, pressure only acts in the downward direction.
False.
In a fluid at rest, all points are in equilibrium, so pressure acts in all directions at each point.
In deriving Δp = ρgΔh, how is the weight of the fluid above area A expressed in terms of density, area, height and g?
$W = ρ A h g$
Define upthrust.
Upthrust (or buoyancy force) is a force which pushes upwards on an object submerged in a fluid.
What causes the force of upthrust on a submerged object?
The difference in hydrostatic pressure between the bottom and top of the object — pressure is greater at the bottom because it is at a greater depth.
Why is upthrust significantly greater in liquids than in gases?
Liquids are much denser than gases, so the hydrostatic pressure difference (and resulting upthrust) is greater.
What condition must be met for an object to float in a fluid?
The object's density must be less than the density of the fluid it is immersed in.
True or False?
An object's apparent weight increases when it is immersed in a fluid.
False.
Apparent weight decreases, because upthrust acts upwards and partially supports the object's weight.
Upthrust is directly proportional to the .......... difference between the top and bottom of a submerged object.
Upthrust is directly proportional to the pressure difference between the top and bottom of a submerged object.
State Archimedes' Principle.
An object submerged in a fluid at rest experiences an upward upthrust equal to the weight of the fluid displaced by the object.
What is the equation for the magnitude of upthrust according to Archimedes' Principle?
$F = ρ g V$
- ρ = density of the fluid (kg m^-3)
- g = gravitational field strength (N kg^-1)
- V = volume of fluid displaced (m³)
Under what condition does an object float, according to Archimedes' Principle?
It floats when the magnitude of the upthrust equals the weight of the object.
Explain, using Archimedes' Principle, why ships made of dense materials such as steel are able to float.
A ship's shape means it displaces a volume of water whose weight equals the ship's own weight, so the upthrust balances the weight.
True or False?
An object placed in a fluid always sinks until it reaches the bottom.
False.
An object sinks only until the weight of the fluid it displaces equals its own weight, at which point it floats.
Since m = ρV, the upthrust force F = mg can also be written as F = .........., which is the weight of the fluid displaced.
Since m = ρV, the upthrust force F = mg can also be written as F = ρVg, which is the weight of the fluid displaced.

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