Unit 1 definitions

Question 1

(Stress strain graph) Limit of proportionality:

Answer 1

Up to this point stress is proportional to strain / obeys Hooke’s law / Force proportional to extension

Question 2

Elastic Limit:

Answer 2

Point after which there would be some permanent/plastic deformation would occur

Question 3

Yield point:

Answer 3

Point at which plastic deformation begins / point at which material shows a larger increase in strain for a smaller increase in stress

Question 4

Tensile strength/Maximum tensile stress:

Answer 4

Greatest stress before fracturing

Question 5

Ultimate Tensile Stress:

Answer 5

Stress at fracture

Question 6

Young’s Modulus:

Answer 6

Gradient of stress/strain graph in linear region

Question 7

Stress-Strain Graph

Answer 7

Limit of proportionality: Up to this point stress is proportional to strain / obeys Hooke’s law / Force proportional to extension (A)

Elastic Limit: Point after which there would be some permanent/plastic deformation would occur (B)

Yield point: Point at which plastic deformation begins / point at which material shows a larger increase in strain for a smaller increase in stress (C)

Tensile strength/Maximum tensile stress: Greatest stress before fracturing (D)

Ultimate Tensile Stress: Stress at fracture (E)

Question 8

Hooke’s Law:

Answer 8

The force is proportional to extension i.e. the graph passes through the origin and is straight.

Question 9

Compressive/tensile strain:

Answer 9

Compressive is a decrease in extension/negative extension. Tensile is an increase in extension/positive extension

Question 10

Plastic deformation:

Answer 10

Doesn’t return to original shape/length OR stays stretched OR permanently deformed … when force/stress removed

Question 11

Elastic deformation:

Answer 11

Returns to original shape/length when force/stress removed

Question 12

Ductile:

Answer 12

Undergoes large permanent/plastic deformation under tension OR can be easily drawn into wires

N.B. All ductile materials are malleable but not necessarily the other way round

Question 13

Malleable:

Answer 13

Undergoes large permanent/plastic deformation under compression OR can be easily hammered into shape/rolled into sheets

N.B. All ductile materials are malleable but not necessarily the other way round

Question 14

Brittle:

Answer 14

Breaks with no/little plastic deformation. Absorbs little energy before fracture. Shatters when subject to impact / sudden force

Question 15

Tough:

Answer 15

Able to absorb lots of energy without failure/in the plastic region OR can withstand impact forces/shocks

Question 16

Stiff:

Answer 16

Gradient of stress/strain graph is high OR large stress for a small deformation /strain OR Large Young modulus

Question 17

Strong:

Answer 17

Large/high breaking stress

Question 18

Hard:

Answer 18

Resists surface indentation/scratching

Question 19

Laminar flow:

Answer 19

No abrupt change in velocity/direction speed of flow OR flows in layers/ streamlines with no mixing/in parallel OR velocity at a point is constant

Question 20

Turbulent flow:

Answer 20

Mixing of layers OR contains eddies/vortices OR abrupt/random changes in speed or direction

Question 21

Draw a diagram showing laminar and turbulent flow around an object

e.g. air aound a chimney stack or water around a bridge support

Answer 21

Question 22

Vector:

Answer 22

A quantity with magnitude and direction

Question 23

Scalar:

Answer 23

A quantity with magnitude only

Question 24

Centre of Mass:

Answer 24

Point where all of the weight (can be assumed to) act OR the point around which the net moment is zero

Question 25

N I:

Answer 25

An object will have no acceleration/remain at constant velocity/at rest/in uniform motion in straight line unless unbalanced/net/resultant force acts on it

Question 26

N II:

Answer 26

The acceleration of an object is proportional to the net force acting on it OR ΣF = ma with Σ, F, m and a defined

Question 27

N III:

Answer 27

All forces occur in pairs of equal size and type but in opposite directions (on different bodies). If object A exerts a force on object B then object B exerts an equal and opposite force on object A