KCL Section 2: Force-extension graphs (Materials) Flashcards Preview

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Flashcards in KCL Section 2: Force-extension graphs (Materials) Deck (30)
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1
Q

State three SI base quantities

A

meters second kilograms

2
Q

State 2 SI derived units

A

kgms^-2

kgms^-1

3
Q

Define ‘drag force’

A

Drag is a force acting opposite to the relative motion of any object moving with respect to a surrounding fluid.

4
Q

________ deformation: the material will return to its original shape when the deforming force is removed
________ deformation: the material will remain deformed when the deforming force is removed

A

Elastic deformation: the material will return to its original shape when the deforming force is removed
Plastic deformation: the material will remain deformed when the deforming force is removed

5
Q

Can a single material often show both types of deformation, depending on the size of the force applied?

A

Yes

6
Q

—–FLASHCARD NOT READY YET——-

A=
B=
C=

A

A: the limit of proportionality
O-A: Hooke’s Law applies
B: the elastic limit
C: the yield point

7
Q

What are the y- and x-axes labelled on a force-extension graph?

A
y = N
x = m
8
Q

What does an upwards slope represent?

A

elastic region

9
Q

What does a downwards slope represent?

A

plastic region

10
Q

What does a linear section of a graph show?

A

F is proportional to the change in x

11
Q

What does a curved section of a graph show?

A

F is not proportional to the change in x

12
Q

What’s happening inside the material?

In the elastic region
Beyond the elastic limit (in the plastic region)
Beyond the yield point (still in the plastic region)

A

What’s happening inside the material?

IN THE ELASTIC REGION: the bonds between atoms increase in length, due to the forces on the material, but revert to their usual length when the force is removed and the atoms return to their equilibrium positions.
BEYOND THE ELASTIC REGION: the arrangement of atoms has changed and the material has undergone permanent (plastic) deformation. It may contract when the force is removed, but not to its original shape.
BEYOND THE YIELD POINT: the atoms move as layers, which slide over each other with no restorative forces. The material will not contract when the force is removed.

13
Q

.

A

.

14
Q

Explain the meaning of the following terms relating to a copper wire that has been loaded to breaking point:

a) limit of proportionality
b) elastic limit
c) yield point
d) plastic flow.

A

a) Limit of proportionality is the point where Hooke’s law ceases to be obeyed.
b) elastic limit is the point beyond which the wire will not regain its original shape when the deforming force is removed.
c) Yield point is at the onset of plastic flow.
d) Plastic flow is the region where [be wire deforms plastically. Layers of atoms slide over each other and when the load is removed there will be no change in the length of the wire.

15
Q

What is elastic strain energy and how is it calculated?

A

Elastic strain energy represents the ability of a material to do work as it returns to its original dimensions.
It is calculated as work done = average force x distance moved
W = FavΔx
For an object obeying Hooke’s Law, this becomes: Eel = ½F∆x
For an object not obeying Hooke’s Law throughout, the area underneath a graph should be calculated.

16
Q

A spring is 0.38 m long. When it is pulled by a force of 2.0 N, it stretches to 0.42 m. What is the spring constant? Assume that the spring behaves elastically.

A

50Nm^-1

17
Q

A spring is 0.38 m long. When it is pulled by a force of 2.0 N, it stretches to 0.42 m. What is the spring constant? Assume that the spring behaves elastically.

A

50Nm^-1

18
Q

A spring is 32 cm long. It is stretched by a force of 6.0 N until it is 54 cm long. How much energy is stored in the stretched spring?
Hint: make sure the distance measurements are always In metres!

A

0.66J

19
Q

Force-extension graphs are drawn for two different wires. How would you determine

i) which wire was stiffer?
ii) which was tougher?
A

i) Stiffer material will have a steeper gradient.

ii) Tougher material has a greater area under the curve.

20
Q

If the wires were loaded until they snapped, how would you know if either wire was brittle?

A

The brittle line will show little or no plastic deformation when it breaks.

21
Q

A load of 12 kg causes a wire to extend by 2.5mm. If the wire obeys Hooke’s law

a) calculate the stiffness of the wire
b) calculate the elastic potential energy transferred to the wire.

A
  1. 7 x 10^4 Nm^-1

0. 15J

22
Q

Explain the statement, ‘natural rubber Is a polymer’.

A

A polymer Is made up of molecules consisting of many atoms (mainly carbon and hydrogen) in long chains.

23
Q

How would you estimate the value of the work done stretching a rubber band from the resulting force-extension graph for the band?

A

Work done = area under the graph.
This can be estimated by calculating the energy represented by each square and counting the squares, or by drawing angles, rectangles or trapeziums that give an approximate fit of the curve and finding their areas,

24
Q

What is tension?

A

Tension is a force acting within a material in a direction that would extend the material.

25
Q

What is extension?

A

Extension is an increase in size of a material sample caused by tension force.

26
Q

What is compression?

A

Compression is a force acting within a menial in a dire.. that would squash the material. A.. the decrease in aire °fa material sample under a compressive force.

27
Q

What is the limit of proportionality?

A

The limit of proportionality is the maximum extension (or strain) that an object (or sample) can exhibit which is still proportional to the load (or stress/applied

28
Q

What is a material’s elastic limit?

A

A material’s elastic limit is the maximum extension or compression that material can undergo and still return to it original dimensions when the force is removed.

29
Q

What is the spring constant?

A

The spring constant is the Hooke’s law constant of proportionality, k is for a spring under tension.

30
Q

What is hysteresis

A

For the extension of a material sample, hysteresis is where extension under a certain load will be different depending on it’s history of past loads and extensions.

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