Density is the mass per unit volume of an object.

When converting a cubic unit, such as cm 3 to m 3 , why must the conversion factor be cubed rather than applied once?

Because volume is a cubic quantity, so all three dimensions must be converted, e.g. 1 cm 3 = 1 / (100) 3 m 3 = 1 × 10 -6 m 3 .

When converting a smaller unit to a larger one, you .......... the value by the conversion factor.

When converting a smaller unit to a larger one, you divide the value by the conversion factor.

True or False? A balloon is denser than a small bar of lead.

False. Density depends on mass per unit volume , not size. A balloon has a much lower density than lead despite occupying a larger volume.

What two quantities do you need to calculate the density of an object?

Its mass and its volume , with volume calculated using the equation appropriate to the object's shape.

Define upthrust (Archimedes' principle).

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

Under what condition does a submerged object float?

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

Outline the two steps used to calculate the magnitude of upthrust on a submerged object.

Find the volume of the submerged object, which equals the volume of displaced fluid Find the weight of that displaced fluid using m = ρV and W = mg

The volume of the displaced fluid is equal to the .......... of the submerged object.

The volume of the displaced fluid is equal to the volume of the submerged object.

True or False? An object always sinks to the bottom of a fluid unless it is less dense than the fluid.

False. An object sinks until the weight of the fluid it displaces equals its own weight . If this balance is reached before the object reaches the bottom, it floats .

Define viscous drag .

Viscous drag is the frictional force between an object and a fluid which opposes the motion between the object and the fluid.

List the four conditions required for Stokes' law to apply.

The flow is laminar The object is small The object is spherical Motion between the object and fluid is at a slow speed

In .......... flow, all the layers of a fluid move in the same direction and do not mix.

In laminar flow, all the layers of a fluid move in the same direction and do not mix.

True or False? Liquids become more viscous as temperature increases.

False. Liquids become less viscous as temperature increases, while gases become more viscous as temperature increases.

At terminal velocity, how do the forces on a sphere falling through a fluid balance?

The weight of the sphere equals the sum of the upthrust and the viscous drag force: W = U + F d .

Define terminal velocity in the context of this experiment.

Terminal velocity is the constant velocity reached by the falling ball bearing when the forces acting on it are balanced (weight = upthrust + viscous drag).

State the independent and dependent variables in the investigation of viscosity using falling ball bearings.

Independent variable: weight of the ball bearing , W s Dependent variable: terminal velocity , v term

Why must the highest rubber band be positioned well below the surface of the liquid?

To ensure the ball bearing has already reached terminal velocity by the time it passes the first band.

The measuring cylinder must have a large diameter compared to the ball bearing to avoid the possibility of .......... flow.

The measuring cylinder must have a large diameter compared to the ball bearing to avoid the possibility of turbulent flow.

True or False? Only one repeat is needed for each diameter of ball bearing tested.

False. The measurement should be repeated at least three times for balls of each diameter tested.

Why is a magnet used to remove the ball bearings from the measuring cylinder?

Steel ball bearings are magnetic , so a magnet held against the outside wall can retrieve them from the bottom of the tube without disturbing the liquid.

International A Level (IAL)PhysicsEdexcelFlashcards1. Mechanics & MaterialsDensity, Upthrust & Viscous Drag

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

Exam code: YPH11

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FrontDensity
Define density.
FrontDensity
State the equation for density and define each symbol.
BackDensity
$ρ = \frac{m}{V}$
ρ = density (kg m^-3)
m = mass (kg)
V = volume (m³)

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Cards in this collection (25)

Define density.
Density is the mass per unit volume of an object.
State the equation for density and define each symbol.
$ρ = \frac{m}{V}$
- ρ = density (kg m^-3)
- m = mass (kg)
- V = volume (m³)
When converting a cubic unit, such as cm³ to m³, why must the conversion factor be cubed rather than applied once?
Because volume is a cubic quantity, so all three dimensions must be converted, e.g. 1 cm³ = 1 / (100)³ m³ = 1 × 10^-6 m³.
When converting a smaller unit to a larger one, you .......... the value by the conversion factor.
When converting a smaller unit to a larger one, you divide the value by the conversion factor.
True or False?
A balloon is denser than a small bar of lead.
False.
Density depends on mass per unit volume, not size. A balloon has a much lower density than lead despite occupying a larger volume.
What two quantities do you need to calculate the density of an object?
Its mass and its volume, with volume calculated using the equation appropriate to the object's shape.
Define upthrust (Archimedes' principle).
An object submerged in a fluid at rest experiences an upward buoyancy force (upthrust) equal to the weight of the fluid displaced by the object.
Under what condition does a submerged object float?
It floats when the magnitude of the upthrust equals the weight of the object.
Outline the two steps used to calculate the magnitude of upthrust on a submerged object.
- Find the volume of the submerged object, which equals the volume of displaced fluid
- Find the weight of that displaced fluid using m = ρV and W = mg
The volume of the displaced fluid is equal to the .......... of the submerged object.
The volume of the displaced fluid is equal to the volume of the submerged object.
True or False?
An object always sinks to the bottom of a fluid unless it is less dense than the fluid.
False.
An object sinks until the weight of the fluid it displaces equals its own weight. If this balance is reached before the object reaches the bottom, it floats.
Give the combined equation for calculating upthrust directly, and define the symbols.
$U = ρ V g$
- ρ = density of the fluid (kg m^-3)
- V = volume of displaced fluid (m³)
- g = gravitational field strength (N kg^-1)
Define viscous drag.
Viscous drag is the frictional force between an object and a fluid which opposes the motion between the object and the fluid.
State Stokes' law and define each symbol.
$F = 6 π η r v$
- F = viscous drag force (N)
- η = coefficient of viscosity (N s m^-2 or Pa s)
- r = radius of the object (m)
- v = velocity of the object (m s^-1)
List the four conditions required for Stokes' law to apply.
- The flow is laminar
- The object is small
- The object is spherical
- Motion between the object and fluid is at a slow speed
In .......... flow, all the layers of a fluid move in the same direction and do not mix.
In laminar flow, all the layers of a fluid move in the same direction and do not mix.
True or False?
Liquids become more viscous as temperature increases.
False.
Liquids become less viscous as temperature increases, while gases become more viscous as temperature increases.
At terminal velocity, how do the forces on a sphere falling through a fluid balance?
The weight of the sphere equals the sum of the upthrust and the viscous drag force: W = U + F_d.
Define terminal velocity in the context of this experiment.
Terminal velocity is the constant velocity reached by the falling ball bearing when the forces acting on it are balanced (weight = upthrust + viscous drag).
State the independent and dependent variables in the investigation of viscosity using falling ball bearings.
- Independent variable: weight of the ball bearing, W_s
- Dependent variable: terminal velocity, v_term
Why must the highest rubber band be positioned well below the surface of the liquid?
To ensure the ball bearing has already reached terminal velocity by the time it passes the first band.
The measuring cylinder must have a large diameter compared to the ball bearing to avoid the possibility of .......... flow.
The measuring cylinder must have a large diameter compared to the ball bearing to avoid the possibility of turbulent flow.
True or False?
Only one repeat is needed for each diameter of ball bearing tested.
False.
The measurement should be repeated at least three times for balls of each diameter tested.
Why is a magnet used to remove the ball bearings from the measuring cylinder?
Steel ball bearings are magnetic, so a magnet held against the outside wall can retrieve them from the bottom of the tube without disturbing the liquid.
State the equation used to calculate the coefficient of viscosity, η, from this experiment.
$η = \frac{2 r^{2} g (ρ_{s} - ρ_{f})}{9 v_{t e r m}}$
where ρ_s = density of the sphere and ρ_f = density of the fluid.

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