(L11) S&F L1 - Elasticity: stress & strain

Question 1

What are the 4 states of matter?

Answer 1

liquid, gas, solid, plasma

Question 2

What is a solid?

Answer 2

not very dancey.
- molecules oscillate around more/less fixed centres
- amplitude of vibration is small and fixed centres frequently form spatial patterns
- long range order

Question 3

What does spatial pattern and long range order mean?

Answer 3

There is a pattern formed over a long range within solids.

Question 4

What is a liquid?

Answer 4

sorta dancey!
-intermolecular distances are larger, amplitudes oscillation and fixed centres is larger
- centres aren’t fixed, take shape of container
- show regularity of order in immediate neighbourhood of few molecule. short range order

Question 5

What is short range order?

Answer 5

There is a spatial pattern within the short range of a neighbourhood of molecules

Question 6

What is a gas?

Answer 6

NOT CARING ABOUT DIE NEIGHBOUR! DANCE DANCE!
- Greater kinetic energy of molecules
- widely seperated, evenly distributed in container
- experience very small attractive forces
- move in straight line until they collide with each other or wall

Question 7

What occurs when an oject is subjected to equal and opposite balanced forces?

Answer 7

It undergoes a change in shape, size or both.

Question 8

What is ‘behaving elastically’?

Answer 8

If an object returns to it soriginal shape and size after balanced forces are removed,
it’s said to behave elastically.

Question 9

What is Lo?

Answer 9

Unstressed bar has Inital
length Lo

Question 10

What is stress?

Answer 10

Force over an Area.
Force distributed uniformly across an area..
Units of stress are Pa

Question 11

What is strain?

Answer 11

Measure of the deformation of an object due to stress

Question 12

What’s pulling stress’s effect?

Answer 12

Tensile strain
Tensile strain is positive
unit is unitless as it l/l cancels

Question 13

What’s pushing stress’s effect?

Answer 13

Compressive strain
Compressive strain is negative

Question 14

How does stress relate to strain?

Answer 14

stress is proportional to strain

Question 15

What does young’s modulus, γ, do?

Answer 15

Young’s modulus characterises elastic properties of a material that’s independent of shape or size of the specimen.

Question 16

What is young’s modulus, γ for compressive strain?

Answer 16

units are Pa

Question 17

What is young’s modulus, γ for tensile strain?

Answer 17

units are Pa

Question 18

Young’s modulus is defined for a material only when 3 things:

Answer 18

1. stress is proportional to strain
   2.does not depend on shape, size, or volume of object
2. does depend on the material of the object
   (it’s a measure of ‘stretchiness of a material)

Question 19

What does a small young’s modulus mean compared to a large young’s modulus?

Answer 19

The same stress could be applied to 2 different materials. Each has different young’s modulus.

The smaller y’s modulus happens to resist stress less, so it will deform.
Larger y’s modulus resists stress more. It won’t deform as easily.

Question 20

How to use diameter to find area?

Answer 20

A=π(d/2)^2

Question 21

What is equation for young’s modulus of compression?

Answer 21