PMT Flashcards

1
Q

What is meant by extension and compression of a string?

A
  • Tensile forces act away from the centre of the spring in both directions and will stretch it out causing the spring to extend
  • Forces acting towards the centre of the spring in both directions is called compression
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2
Q

What happens to the spring when tensile/compressive forces are exerted?

A

The spring undergoes ‘tensile deformation’ or ‘compressive deformation’

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3
Q

What is Hooke’s law?

A

In a material showing Hooke’s law, the force applied is directly proportional to the extension in length, up to the limit of proportionality
F =k(change in)x
K= spring constant
X = length

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4
Q

What is meant by tensile stress?

A

The force per unit area

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5
Q

What is tensile strain?

A

A measure of how the material stretches: the extension divided by the original length. This value is a ratio, so it has no units

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6
Q

What is the difference between elastic and plastic deformation?

A

Elastic - when the force is removed, the object will return to its original shape
Plastic - after the force is removed, the object will not return to its original shape (limit of proportionality has been exceeded)

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7
Q

How is energy stored during elastic deformation?

A

The work done is transferred and stored as elastic potential energy

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8
Q

Describe the energy changes that occur during plastic deformation

A

The material is stretched and the energy from the work done is used to break the bonds between the molecules. This causes permanent deformation

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9
Q

What is breaking stress?

A

The amount of stress a material can take without it breaking

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10
Q

what is meant when a material is described as brittle?

A

It does not extend much when a force is applied (tensile strain stays low). The material tends to break rather than stretch under a large force

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11
Q

What is the elastic limit?

A

The point after which plastic deformation occurs. It is sometimes also referred to as the ‘limit of proportionality’

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12
Q

What does the area under a force-extension graph represent?

A

The energy stored in the material

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13
Q

Give the equation that calculates elastic strain energy in terms of spring constant and extension

A

E = 1/2 k (change in)L^2

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14
Q

What is Young’s Modulus?

A

Young’s modulus = tensile stress / tensile strain

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15
Q

How do you find the Young’s modulus from an stress-strain graph?

A

Using the gradient of the line

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