The mass per unit volume of an object.

What two units are commonly used for density ?

g cm -3 when mass is in grams and volume in cm 3 kg m -3 when mass is in kilograms and volume in m 3

Objects made from .......... materials typically have a lower mass

Objects made from low-density materials typically have a lower mass

How can you find the volume of a regularly shaped object?

Calculate it from the object's dimensions using the appropriate volume equation for its shape (e.g. cuboid, sphere or cylinder).

True or False? A less dense material always occupies a smaller volume than a denser one

False. Density depends on both mass and volume. A balloon is less dense than a small bar of lead yet occupies a much larger volume.

The upward buoyancy force acting on an object submerged in a fluid, equal to the weight of the fluid displaced by the object.

State Archimedes' principle .

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

An object floats when the magnitude of the upthrust equals the .......... of the object

An object floats when the magnitude of the upthrust equals the weight of the object

True or False? A floating object displaces a volume of fluid equal to its own volume

False. A floating object displaces a weight of fluid equal to its own weight, not an equal volume. A boat floats because it pushes aside water weighing the same as the boat.

Define viscous drag .

The frictional force between an object and a fluid which opposes the relative motion between the object and the fluid.

The rate of flow of a fluid is .......... proportional to the coefficient of viscosity

The rate of flow of a fluid is inversely proportional to the coefficient of viscosity

State the conditions under which Stokes' law can be applied.

the flow is laminar the object is small the object is spherical the motion between object and fluid is slow

Distinguish between laminar and turbulent flow.

Laminar — layers of fluid move in the same direction and do not mix Turbulent — layers move in different directions and do mix

As temperature increases, the viscosity of a liquid tends to ..........

As temperature increases, the viscosity of a liquid tends to decrease

True or False? The viscosity of a gas decreases as its temperature increases

False. Unlike liquids, the viscosity of a gas increases as temperature rises, because it depends on the rate of intermolecular collisions.

What is the aim of Core Practical 4: Investigating Viscosity?

To determine the viscosity of a fluid by timing small spheres of known weight as they fall through it at terminal velocity .

State the independent, dependent and control variables in the viscosity investigation.

Independent — weight of the ball bearing Dependent — terminal velocity Control — the fluid being tested and its temperature

The highest rubber band must be low enough that the ball is falling at .......... before it reaches the band

The highest rubber band must be low enough that the ball is falling at terminal velocity before it reaches the band

Why must the cylinder be much wider than the ball bearing?

To avoid turbulent flow around the ball, which would invalidate Stokes' law. The ball should also fall down the centre of the tube to avoid wall pressure effects.

How are the ball bearings removed from the bottom of the tube?

By holding a magnet against the outside wall of the measuring cylinder to draw them up.

True or False? Timing of the fall should begin the moment the ball bearing is released

False. Timing begins only once the ball has reached terminal velocity (at the first rubber band). Before then it is still accelerating, so Stokes' law would not apply.

A LevelPhysicsEdexcelFlashcards4. MaterialsDensity, Upthrust & Viscous Drag

Density, Upthrust & Viscous Drag (Edexcel A Level Physics): Flashcards

Exam code: 9PH0

1/27

0Still learning

Know0

FrontDensity
Define density.
FrontDensity
What two units are commonly used for density?
BackDensity
g cm^-3 when mass is in grams and volume in cm³
kg m^-3 when mass is in kilograms and volume in m³

Was this flashcard helpful?

Cards in this collection (27)

Define density.
The mass per unit volume of an object.
What is the equation for density?
$ρ = \frac{m}{V}$
where m is the mass and V is the volume of the object.
What two units are commonly used for density?
- g cm^-3 when mass is in grams and volume in cm³
- kg m^-3 when mass is in kilograms and volume in m³
Objects made from .......... materials typically have a lower mass
Objects made from low-density materials typically have a lower mass
How can you find the volume of a regularly shaped object?
Calculate it from the object's dimensions using the appropriate volume equation for its shape (e.g. cuboid, sphere or cylinder).
True or False?
A less dense material always occupies a smaller volume than a denser one
False.
Density depends on both mass and volume. A balloon is less dense than a small bar of lead yet occupies a much larger volume.
Define upthrust.
The upward buoyancy force acting on an object submerged in a fluid, equal to the weight of the fluid displaced by the object.
State Archimedes' principle.
An object submerged in a fluid at rest experiences an upward force (upthrust) equal to the weight of the fluid displaced by the object.
An object floats when the magnitude of the upthrust equals the .......... of the object
An object floats when the magnitude of the upthrust equals the weight of the object
What single equation gives the upthrust on a fully submerged object?
$W = ρ V g$
where ρ is the fluid density, V is the volume displaced and g is the gravitational field strength.
Describe the steps used to calculate the upthrust on a submerged object.
- Find the volume of the submerged object (equal to the volume of fluid displaced)
- Find the mass of the displaced fluid using $m = ρ V$
- Find its weight using $W = m g$ — this equals the upthrust
True or False?
A floating object displaces a volume of fluid equal to its own volume
False.
A floating object displaces a weight of fluid equal to its own weight, not an equal volume. A boat floats because it pushes aside water weighing the same as the boat.
Define viscous drag.
The frictional force between an object and a fluid which opposes the relative motion between the object and the fluid.
What is Stokes' law for viscous drag?
$F = 6 π η r v$
where η = coefficient of viscosity (Pa s or N s m^-2), r = radius of the object and v = velocity.
The rate of flow of a fluid is .......... proportional to the coefficient of viscosity
The rate of flow of a fluid is inversely proportional to the coefficient of viscosity
State the conditions under which Stokes' law can be applied.
- the flow is laminar
- the object is small
- the object is spherical
- the motion between object and fluid is slow
Distinguish between laminar and turbulent flow.
- Laminar — layers of fluid move in the same direction and do not mix
- Turbulent — layers move in different directions and do mix
As temperature increases, the viscosity of a liquid tends to ..........
As temperature increases, the viscosity of a liquid tends to decrease
For a sphere falling at terminal velocity through a fluid, what is the expression for terminal velocity, and how does it depend on radius and viscosity?
$v = \frac{2 r^{2} g (ρ_{s} - ρ_{f})}{9 η}$
Terminal velocity is directly proportional to r² (the square of the radius) and inversely proportional to η (the viscosity of the fluid).
True or False?
The viscosity of a gas decreases as its temperature increases
False.
Unlike liquids, the viscosity of a gas increases as temperature rises, because it depends on the rate of intermolecular collisions.
What is the aim of Core Practical 4: Investigating Viscosity?
To determine the viscosity of a fluid by timing small spheres of known weight as they fall through it at terminal velocity.
State the independent, dependent and control variables in the viscosity investigation.
- Independent — weight of the ball bearing
- Dependent — terminal velocity
- Control — the fluid being tested and its temperature
The highest rubber band must be low enough that the ball is falling at .......... before it reaches the band
The highest rubber band must be low enough that the ball is falling at terminal velocity before it reaches the band
Which equation is used to find the viscosity in this experiment?
$η = \frac{2 r^{2} g (ρ_{s} - ρ_{f})}{9 v_{t e r m}}$
Why must the cylinder be much wider than the ball bearing?
To avoid turbulent flow around the ball, which would invalidate Stokes' law. The ball should also fall down the centre of the tube to avoid wall pressure effects.
How are the ball bearings removed from the bottom of the tube?
By holding a magnet against the outside wall of the measuring cylinder to draw them up.
True or False?
Timing of the fall should begin the moment the ball bearing is released
False.
Timing begins only once the ball has reached terminal velocity (at the first rubber band). Before then it is still accelerating, so Stokes' law would not apply.

Sign up to unlock flashcards

By signing up you agree to our Terms and Privacy Policy

Previous:E.M.F & Modelling ResistanceNext:Stretching Materials