Deformation is a change in the size and shape of a body caused by forces.

Define tensile force .

A tensile force occurs when two forces act on a body to stretch it.

Define compressive force .

A compressive force occurs when two forces act on a body to compress it.

What happens to a spring when a load is applied to it?

The load produces a tensile force , causing the spring to extend .

When a force is applied to a spring in the opposite direction to the load, the spring ..........

When a force is applied to a spring in the opposite direction to the load, the spring compresses .

True or False? Applying a load to a spring always causes it to compress.

False. Applying a load produces a tensile force , causing the spring to extend . Compression occurs when the force is applied in the opposite direction.

Hooke's law states that the extension of a material is directly proportional to the applied force (load), up to the limit of proportionality .

Define the spring constant .

The spring constant , k , is the force per unit extension up to the limit of proportionality, and measures the stiffness of a material.

What does a larger spring constant tell you about a material?

The larger the spring constant, the stiffer the material.

Hooke's law states that extension is directly proportional to the applied force up to the ..........

Hooke's law states that extension is directly proportional to the applied force up to the limit of proportionality .

True or False? On a graph of extension (vertical axis) against force (horizontal axis), the gradient of the straight-line region is equal to the spring constant.

False. When extension is plotted against force, the gradient equals 1 ÷ spring constant , not the spring constant itself.

Define the limit of proportionality .

The limit of proportionality is the point beyond which Hooke's law is no longer true, i.e. the extension is no longer proportional to the applied force.

Define the elastic limit .

The elastic limit is the maximum amount a material can be stretched and still return to its original length; it always occurs after the limit of proportionality.

What is a hysteresis loop ?

The area between the loading and unloading curves for a material such as rubber, representing the work done that is transferred to thermal energy .

Polyethene does not obey Hooke's law and experiences .......... deformation when any force is applied to it.

Polyethene does not obey Hooke's law and experiences plastic deformation when any force is applied to it.

True or False? A material that has undergone plastic deformation returns to its original length once the force is removed.

False. Plastic deformation causes a permanent extension ; the material does not return to its original length.

In the force-extension investigation, which variable is the independent variable?

The force (load) , in newtons; extension is the dependent variable.

Define elastic potential energy .

Elastic potential energy is the energy stored within a material when it is stretched or compressed.

How is the work done in stretching a material found from a force-extension graph?

It is equal to the area under the force-extension graph .

Why is the area under a force-extension graph a right-angled triangle when a material obeys Hooke's law?

Because the graph is a straight line through the origin in this region, so the area under it forms a triangle.

For a material that does not obey Hooke's law, the area under the force-extension graph is found by splitting the graph into .......... and adding them together.

For a material that does not obey Hooke's law, the area under the force-extension graph is found by splitting the graph into separate segments and adding them together.

True or False? When a stretched wire suddenly breaks, its elastic potential energy converts into gravitational potential energy.

False. The elastic potential energy converts into kinetic energy (EPE = KE).

What does v ∝ x show about a wire that breaks under stress?

The greater the extension of the wire before breaking, the greater the speed it will have on breaking.

Define tensile stress .

Tensile stress is the force exerted per unit cross-sectional area of a material.

Define tensile strain .

Tensile strain is the extension per unit length of a material.

Define ultimate tensile strength .

The ultimate tensile strength is the maximum amount of load or stress a material can handle until it fractures and breaks.

What are the units of tensile stress?

Pascals (Pa) — the same units as pressure, since both are force per unit area.

Tensile strain is a .......... quantity, because it is the ratio of two lengths.

Tensile strain is a dimensionless quantity, because it is the ratio of two lengths.

True or False? Tensile strain always has units of metres.

False. Tensile strain is dimensionless (unitless), as it is the ratio of extension to original length, though it is sometimes expressed as a percentage.

Define the Young modulus .

The Young modulus measures the ability of a material to withstand changes in length with an added load.

What does the gradient of a linear stress-strain graph represent?

The Young modulus of the material.

In the Young modulus experiment, what are the independent and dependent variables?

Independent variable: force (load) . Dependent variable: extension .

To reduce the uncertainty in the cross-sectional area, the diameter of the wire should be measured in .......... and an average calculated.

To reduce the uncertainty in the cross-sectional area, the diameter of the wire should be measured in several places and an average calculated.

True or False? If a wire is stretched past its elastic limit, it will return to its original length once the load is removed.

False. Beyond the elastic limit, the wire is permanently deformed and will not return to its original length.

Why should safety goggles be worn throughout the Young modulus experiment?

In case the wire snaps under tension.

Define a brittle material.

A brittle material fractures before any plastic deformation occurs.

Define a ductile material.

A ductile material can withstand large plastic deformation without breaking.

Define a polymeric material.

A polymeric material is made up of long, repeating chains of molecules.

What is yield stress ?

The force per unit area at which a material extends plastically for a small increase in stress.

What is the breaking stress of a material?

The maximum stress a material can withstand before it fractures .

How is the elastic strain energy stored per unit volume found from a stress-strain graph?

It is equal to the area under the straight-line (Hooke's law) region of the graph.

For a polymeric material, the unloading curve differs from the loading curve because some energy has been lost as .......... .

For a polymeric material, the unloading curve differs from the loading curve because some energy has been lost as thermal energy .

True or False? Ductile materials show no plastic deformation before breaking.

False. Ductile materials undergo significant plastic deformation , stretching into a new shape, before they break; it is brittle materials that show little to no plastic deformation.

Define elastic deformation .

Elastic deformation occurs when, once the load is removed, the object returns to its original shape.

Define plastic deformation .

Plastic deformation occurs when the material is permanently deformed and does not return to its original shape or length once the load is removed.

What feature of a force-extension graph identifies the elastic region ?

A straight line through the origin, showing that extension is proportional to the applied force.

What feature of a force-extension graph identifies the plastic region ?

The graph starts to curve , showing that extension is no longer proportional to the applied force.

How does a brittle material behave on a force-extension graph?

It breaks with little elastic and insignificant plastic deformation , e.g. glass and concrete.

How does a ductile material behave on a force-extension graph?

It has a larger plastic region and stretches into a new shape before breaking, e.g. copper.

After plastic deformation, the gradient of the unloading line stays the same as the loading line because the .......... between the bonds are unchanged.

After plastic deformation, the gradient of the unloading line stays the same as the loading line because the intermolecular forces between the bonds are unchanged.

A LevelPhysicsOCRFlashcards3. Forces & MotionMaterials

Materials (OCR A Level Physics): Flashcards

Exam code: H556

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FrontDeformation & Compression
Define deformation.

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Cards in this collection (55)

Define deformation.
Deformation is a change in the size and shape of a body caused by forces.
Define tensile force.
A tensile force occurs when two forces act on a body to stretch it.
Define compressive force.
A compressive force occurs when two forces act on a body to compress it.
What happens to a spring when a load is applied to it?
The load produces a tensile force, causing the spring to extend.
When a force is applied to a spring in the opposite direction to the load, the spring ..........
When a force is applied to a spring in the opposite direction to the load, the spring compresses.
True or False?
Applying a load to a spring always causes it to compress.
False.
Applying a load produces a tensile force, causing the spring to extend. Compression occurs when the force is applied in the opposite direction.
Define Hooke's law.
Hooke's law states that the extension of a material is directly proportional to the applied force (load), up to the limit of proportionality.
What equation represents Hooke's law?
$F = k x$
where F is the applied force (N), k is the spring constant (N m^-1) and x is the extension (m).
Define the spring constant.
The spring constant, k, is the force per unit extension up to the limit of proportionality, and measures the stiffness of a material.
What does a larger spring constant tell you about a material?
The larger the spring constant, the stiffer the material.
Hooke's law states that extension is directly proportional to the applied force up to the ..........
Hooke's law states that extension is directly proportional to the applied force up to the limit of proportionality.
True or False?
On a graph of extension (vertical axis) against force (horizontal axis), the gradient of the straight-line region is equal to the spring constant.
False.
When extension is plotted against force, the gradient equals 1 ÷ spring constant, not the spring constant itself.
Define the limit of proportionality.
The limit of proportionality is the point beyond which Hooke's law is no longer true, i.e. the extension is no longer proportional to the applied force.
Define the elastic limit.
The elastic limit is the maximum amount a material can be stretched and still return to its original length; it always occurs after the limit of proportionality.
What does the gradient of the straight-line region of a force-extension graph represent?
The force constant, k.
What is a hysteresis loop?
The area between the loading and unloading curves for a material such as rubber, representing the work done that is transferred to thermal energy.
Polyethene does not obey Hooke's law and experiences .......... deformation when any force is applied to it.
Polyethene does not obey Hooke's law and experiences plastic deformation when any force is applied to it.
True or False?
A material that has undergone plastic deformation returns to its original length once the force is removed.
False.
Plastic deformation causes a permanent extension; the material does not return to its original length.
In the force-extension investigation, which variable is the independent variable?
The force (load), in newtons; extension is the dependent variable.
Define elastic potential energy.
Elastic potential energy is the energy stored within a material when it is stretched or compressed.
How is the work done in stretching a material found from a force-extension graph?
It is equal to the area under the force-extension graph.
Why is the area under a force-extension graph a right-angled triangle when a material obeys Hooke's law?
Because the graph is a straight line through the origin in this region, so the area under it forms a triangle.
What equation gives the elastic potential energy stored in a material obeying Hooke's law?
$E_{p} = \frac{1}{2} k x^{2}$
where k is the force constant (N m^-1) and x is the extension (m).
For a material that does not obey Hooke's law, the area under the force-extension graph is found by splitting the graph into .......... and adding them together.
For a material that does not obey Hooke's law, the area under the force-extension graph is found by splitting the graph into separate segments and adding them together.
True or False?
When a stretched wire suddenly breaks, its elastic potential energy converts into gravitational potential energy.
False.
The elastic potential energy converts into kinetic energy (EPE = KE).
What does v ∝ x show about a wire that breaks under stress?
The greater the extension of the wire before breaking, the greater the speed it will have on breaking.
Define tensile stress.
Tensile stress is the force exerted per unit cross-sectional area of a material.
Define tensile strain.
Tensile strain is the extension per unit length of a material.
Define ultimate tensile strength.
The ultimate tensile strength is the maximum amount of load or stress a material can handle until it fractures and breaks.
What are the units of tensile stress?
Pascals (Pa) — the same units as pressure, since both are force per unit area.
Tensile strain is a .......... quantity, because it is the ratio of two lengths.
Tensile strain is a dimensionless quantity, because it is the ratio of two lengths.
True or False?
Tensile strain always has units of metres.
False.
Tensile strain is dimensionless (unitless), as it is the ratio of extension to original length, though it is sometimes expressed as a percentage.
Define the Young modulus.
The Young modulus measures the ability of a material to withstand changes in length with an added load.
What equation gives the Young modulus, E?
$E = \frac{stress}{strain}$
What does the gradient of a linear stress-strain graph represent?
The Young modulus of the material.
In the Young modulus experiment, what are the independent and dependent variables?
Independent variable: force (load). Dependent variable: extension.
To reduce the uncertainty in the cross-sectional area, the diameter of the wire should be measured in .......... and an average calculated.
To reduce the uncertainty in the cross-sectional area, the diameter of the wire should be measured in several places and an average calculated.
True or False?
If a wire is stretched past its elastic limit, it will return to its original length once the load is removed.
False.
Beyond the elastic limit, the wire is permanently deformed and will not return to its original length.
Why should safety goggles be worn throughout the Young modulus experiment?
In case the wire snaps under tension.
Define a brittle material.
A brittle material fractures before any plastic deformation occurs.
Define a ductile material.
A ductile material can withstand large plastic deformation without breaking.
Define a polymeric material.
A polymeric material is made up of long, repeating chains of molecules.
What is yield stress?
The force per unit area at which a material extends plastically for a small increase in stress.
What is the breaking stress of a material?
The maximum stress a material can withstand before it fractures.
How is the elastic strain energy stored per unit volume found from a stress-strain graph?
It is equal to the area under the straight-line (Hooke's law) region of the graph.
For a polymeric material, the unloading curve differs from the loading curve because some energy has been lost as ...........
For a polymeric material, the unloading curve differs from the loading curve because some energy has been lost as thermal energy.
True or False?
Ductile materials show no plastic deformation before breaking.
False.
Ductile materials undergo significant plastic deformation, stretching into a new shape, before they break; it is brittle materials that show little to no plastic deformation.
Define elastic deformation.
Elastic deformation occurs when, once the load is removed, the object returns to its original shape.
Define plastic deformation.
Plastic deformation occurs when the material is permanently deformed and does not return to its original shape or length once the load is removed.
What feature of a force-extension graph identifies the elastic region?
A straight line through the origin, showing that extension is proportional to the applied force.
What feature of a force-extension graph identifies the plastic region?
The graph starts to curve, showing that extension is no longer proportional to the applied force.
How does a brittle material behave on a force-extension graph?
It breaks with little elastic and insignificant plastic deformation, e.g. glass and concrete.
How does a ductile material behave on a force-extension graph?
It has a larger plastic region and stretches into a new shape before breaking, e.g. copper.
After plastic deformation, the gradient of the unloading line stays the same as the loading line because the .......... between the bonds are unchanged.
After plastic deformation, the gradient of the unloading line stays the same as the loading line because the intermolecular forces between the bonds are unchanged.
True or False?
A material that has undergone plastic deformation returns to its original length once the load is removed.
False.
Plastic deformation is permanent; the material does not return to its original shape or length, even after the load is removed.

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