Materials Flashcards

1
Q

What is the formula for density?

A

p =m/V

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2
Q

What are the units for density?

A

kgm-3 or gcm-3

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3
Q

What is the definition of density?

A

Density is the mass per unit volume

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4
Q

What determines whether an object will float or sink on a fluid?

A

Whether the object is more dense than the fluid (it will sink) or less dense than the fluid (it will float),

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5
Q

What does Hooke’s law state?

A

The extension of a stretched wire, ΔL, is proportional to the load or force F.

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6
Q

How can Hooke’s law be written as a formula?

A

F = kΔL

Where:

F is the force applied (N)

k is the spring constant (Nm-1)

ΔL is the extension (m)

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7
Q

Hooke’s law applies to both stretched wires and stretched and compressed ______

A

Springs

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8
Q

The limit of proportionallity is…

A

The point up to which Hooke’s law is obeyed.

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9
Q

The elastic limit of a material is ……..

A

The point after which the material will become permanently deformed.

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10
Q

Elastic deformation means…..

A

The material will return to its original shape once the forces are removed.

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11
Q

Plastic deformation means…..

A

The material will not return to it’s original length once the forces are removed.

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12
Q

If a pair of opposite forces stretch a material, they’re called ______ forces.

A

If a pair of opposite forces stretch a material, they’re called tensile forces.

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13
Q

If a pair of opposite forces compress a material, they’re called ______ forces.

A

If a pair of opposite forces compress a material, they’re called compressive forces.

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14
Q

Tensile stress is defined as…..

A

the force applied, F, divided by the cross-sectional area, A:

Stress = F/A

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15
Q

What are the units of tensile stress?

A

Nm-2 or Pascals, Pa

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16
Q

Tensile strain is defined as…….

A

The change in length divided by the original lengeth of the material.

17
Q

What are the units of tensile strain?

A

They don’t have units as it’s a ratio.

18
Q

What is the breaking stress of a material?

A

This is the stress that is big enough to break the material.

19
Q

What is the ultmate tensile strength stress of a material?

A

Ultimate tensile strength is the maximum stress that the mateiral can withstand.

20
Q

What is elastic strain energy?

A

It is the potential energy stored when a material is stretched (before the elastic limit is met).

21
Q

What does the area under a force-extension graph tell you?

A

The elastic strain energy

22
Q

What is the formula for calculating elastic strain energy?

A

E = 1/2 k (ΔL)2

23
Q

What does the gradient of a force - extension graph tell you?

A

The gradient of a force-extension graph is the spring constant k, which has units Nm-1

24
Q

How is energy conserved as a stretched wire undergoes plastic deformation?

A

When a material undergoes plastic deformation, energy is used to move atoms in the material away from each other. This energy is dissipated as heat.

25
Q

Describe the energy changes in a spring as it is stretched and released.

A

When a spring is stretched, kinetic energy is transferred to elastic strain energy and stored in the spring. When the spring is released, the elastic strain energy is transferred to kinetic energy.

26
Q

Which point on the graph shows the ultimate tensile strength?

A

E

27
Q

Which point on the graph shows the elastic limit?

A

B

28
Q

Which point on the graph shows the breaking point?

A

F

29
Q

Which point on the graph shows the limit of proportionality?

A

A

30
Q

Name the law that says the extension of a stretched object is proportional to the force applied?

A

Hooke’s Law

31
Q

What is the difference between elastic deformation and plastic deformation?

A

If a material undergoes elastic deformation, the material will return to its original shape and size once the load is removed. Whereas, if the material undergoes plastic deformation, the material will not return to its original shape and size once the load is removed.

32
Q

True or false? The stress-strain graphs of two different sized pieces of nickel have the same gradient.

A

True. The gradient of a stress-strain graph is equal to the Young modulus of the material. Both pieces are made from the same material, so will have the same Young modulus and therefore the same gradient.

33
Q

Why is it better to use a longer wire when using a wire to find the Young modulus?

A

The longer the wire, the bigger the extension for a given force. A bigger extension is easier to see and measure, and it reduces the uncertainty in the measurements.