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4.Mechanics - A level Physics > 4.7 - Bulk Properties of Solids > Flashcards

4.7 - Bulk Properties of Solids Flashcards

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1
Q

What is density?

A

The mass per unit volume of an object.

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2
Q

What are the units of density?

A

kg / m³

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3
Q

What is the equation for density?

A

ρ = m / v
ρ = density
m = mass
v = volume

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4
Q

What is the volume of a sphere, cube and cylinder?

A

sphere - 4/3πr³
cube - d³
cylinder - πr² x l

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5
Q

What is Hooke’s law?

A

The extension of the material is directly proportional to the applied force (load) up to the limit of proportionality.

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6
Q

What is the Hooke’s law equation?

A

F = kΔL
F = force (N)
k = spring constant (Nm⁻¹)
ΔL = extension (m)

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7
Q

What is the spring constant? (k)

A

A property of the material being stretched and measures the stiffness of a material.
(so the larger k is, the stiffer the material is)

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8
Q

What is the extension and compression of a material?

A

Extension - how much the length has increased
Compression - how much the length has decreased

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9
Q

What does a force-extension graph show?

A

The way a material responds to a given force.

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10
Q

What is a brittle material?

A

A material that breaks after its elastic limit is exceeded (like glass).

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11
Q

What is a ductile material?

A

The capacity of a material to deform permanently.

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12
Q

What is the equation for finding the spring constant?

A

k = ΔF/ΔL

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13
Q

What is the limit of proportionality?

A

The point beyond which Hooke’s law is no longer true when stretching a material.

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14
Q

What is the elastic limit?

A

The maximum amount a material can be stretched and still return to its original length. (always after the limit of proportionality)

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15
Q

What is the gradient of a force-extension graph?

A

k, the spring constant.

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16
Q

What is tensile stress?

A

The force exerted per unit cross-sectional area of a material.

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17
Q

What is the equation for tensile stress?

A

σ = F / A
σ = tensile stress (Pa)
F = force applied (N)
A = cross-sectional area (m²)

18
Q

What is the ultimate tensile stress?

A

The maximum force per original cross-sectional area a wire is able to support until it breaks.

19
Q

What is tensile strain?

A

The extension per unit length.

20
Q

What is the equation for tensile strain?

A

ε = ΔL / L
ε = tensile train
ΔL = extension (m)
L = original length (m)

21
Q

What is the yield stress on a stress-strain graph?

A

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

22
Q

How do you calculate the elastic strain energy per unit volume on a stress-strain graph?

A

The area under the Hooke’s Law region of a stress-strain graph.

23
Q

What is the breaking point on a stress-strain graph?

A

The max amount of stress before a material breaks.

24
Q

What is the elastic region of a stress-strain graph?

A

The region of the graph up until the elastic limit.

25
Q

What is the plastic region of a stress-strain graph?

A

The region of the graph after the elastic limit. (Material has deformed permanently).

26
Q

How do you calculate the work done on a force-extension graph?

A

The area under the graph.

27
Q

How do you calculate the elastic strain energy when a material obeys Hooke’s law?

A

E = 1/2FΔL
E = elastic strain energy (or work done) (J)
F = average force (N)
ΔL = extension (m)
Can also be written as
E = 1/2 k(ΔL)² (because of Hooke’s law)

28
Q

What is the property of a material with a high breaking stress?

A

Ductile. (can extend before breaking because of plastic deformation).

29
Q

What is an example of a property with a high breaking stress?

A

Copper (ductile and a good electrical conductor).

30
Q

What comes first, the ultimate tensile stress (UTS) or the breaking point?

A

UTS.

31
Q

When a spring is being vertically extended, when does it have the most GPE?

A

When the mass is at the highest point.

32
Q

When a spring is being vertically extended, when does it have the most KE?

A

When it passes through the equilibrium position at its max speed.

33
Q

When a spring is being vertically extended, when does it have the most EPE? (elastic potential energy)

A

When the spring is at maximum extension.

34
Q

What is elastic deformation?

A

When a material’s load is removed, the object will return to its original shape.

35
Q

What is plastic deformation?

A

When a material’s load is removed and it will not return to its original length/shape.

36
Q

What does a loading-unloading graph of a metal wire look like?

A

As the wire is stretched, it obeys Hooke’s law then plastic deformation occurs. This is the loading.
The unloading is directly proportional to the loading part that obeys Hooke’ law.

37
Q

Why is the unloading line parallel to the loading line with a metal wire?

A

Because k, the spring constant, does not change.

38
Q

What does a loading-unloading graph of a rubber band look like?

A

When the rubber band is extended, it stores a greater amount of strain energy than when it’s being unloaded, so the curve of unloading is always lower.

The work done heating the rubber is between the 2 curves.
The work done by the rubber when it returns to its original shape is the area under the unloading curve.
These added together is the work done in stretching the rubber band originally.

39
Q

What is a shock absorber? (in a car)

A

Elastic objects designed to absorb or dampen the compression and rebound of the spring above a vehicle’s tires.

40
Q

What does a shock absorber do?

A

Dampen the compression and rebound of the spring above a vehicle’s tires which keeps the tires on the road at all times.

41
Q

How do the shock absorbers dampen the compressions and rebounds of a vehicle’s tires?

A

Convert the kinetic energy (from the movement of the car) into thermal energy which is dissipated.

4.Mechanics - A level Physics (3 decks)

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