Statics - Definitions

Question 1

Force

Answer 1

A force is what changes a body’s state of rest or of uniform motion in a straight line
Usually a push or a pull
Is a vector quantity - has both magnitude and direction
Measured in Newton’s (imperial lb)

Question 2

Moment

Answer 2

A moment is the turning effect of a force

Units of Nm

Question 3

Couple

Answer 3

A pair of equal forces acting in opposite directions around a central turning point

Question 4

Scalar quantity

Answer 4

A quantity that has no direction

Question 5

Vector quantity

Answer 5

These are things that have magnitude and direction and act in a straight line direction

Question 6

Resultant force

Answer 6

The effect of two or more vectors. The sum of the vectors is known as the resultant

Question 7

Centre of gravity

Answer 7

Is the point about which a body is perfectly balanced

There is only one centre of gravity

Question 8

Tensile

Answer 8

Pulling apart

Question 9

Compression

Answer 9

Squashing

Question 10

Torsion

Answer 10

Twisting

Question 11

Shear

Answer 11

Pulling/slicing two layers/bodies apart

Question 12

Hooke’s law

Answer 12

The amount of force is doubled, the amount of extension is doubled
(Extension is directly proportional to force)

Question 13

Stress

Answer 13

The magnitude of forces that cause deformation, always accompanied by strain

Question 14

Strain

Answer 14

The deformation of a material due to stress

Question 15

Young’s modulus

Answer 15

The ratio of stress and strain

Question 16

Bulk modulus

Answer 16

This gives the change of volume of a solid substance as the pressure is changed

Question 17

Poisson’s ratio

Answer 17

The ratio of transverse strain to axial strain in a stressed member
Transverse strain - diameter decrease
Axial strain - length increase

Question 18

Hardness

Answer 18

High resistance to indentation or any action to penetrate the surface. Eg, diamond

Question 19

Toughness

Answer 19

The ability to resist breakage when deforming or impact forces are applied to it.

Question 20

Brittleness

Answer 20

Break with little or no change of shape eg glass, cast iron and very hard steel

Question 21

Ductility

Answer 21

Can be stretched into new shapes without breaking apart, will keep their new shape after being stretched, eg wire and copper

Question 22

Plasticity

Answer 22

A material that can be readily forced into a different shape permanently without fracturing. Eg putty in a window frame

Question 23

Elasticity

Answer 23

This is when a substance that has been distorted has a strong tendency to return to its original shape.
Eg steel ball bearing/spring/hard steel

Question 24

Elastic limit

Answer 24

The maximum distorting force that can be applied to the solid without causing permanent distortion

Question 25

Fluid

Answer 25

Anything that can flow, liquids gasses and vapours

Question 26

Vapours

Answer 26

A gas that can be liquified by an increase in pressure without decreasing its temperature.

Question 27

Volatile

Answer 27

This is a liquid that evaporates (vaporises) at normal temperature Eg, petrol, methylated spirits and alcohol

Question 28

Flammable/inflammable

Answer 28

A material that will catch fire easily, eg. Most fuels, light oils and some paints

Question 29

Flash point

Answer 29

The temperature something has to be at before it will catch fire when exposed to a naked flame, aviation fuel: 38°C

Question 30

Toxicity

Answer 30

Refers to how poisonous a substance is.

Question 31

Inert

Answer 31

A substance that will not chemically combine with other substances eg, neon, argon, and helium

Question 32

Bouyancy

Answer 32

The ability of an object to float

Question 33

Archimedes principal

Answer 33

This states that when an object is submerged in a liquid, the object displaces the same volume of water as its volume

Question 34

Buoyant force

Answer 34

The force that a submerged object is held up by, it is equal to the weight of the water being displaced

Question 35

Principle of moments

Answer 35

For an object to balance horizontally the opposing moments must be equal in magnitude

Question 35

Datum

Answer 35

Imaginary line from which all horizontal measurements are taken usually for balance purposes

Question 35

Tension

Answer 35

Stress that is applied causing an increase in the length of a body, known also as tensile stress or axial or normal stress

Question 36

Strength

Answer 36

Tendency to withstand an applied load without failure or plastic deformation

Question 37

Malleability

Answer 37

Tendency to undergo compression without damage malleable materials can be beaten rolled or pressed

Question 38

Pressure

Answer 38

Force applied to the surface of an object, measured in bar, millibar or hectoPascals

Question 39

Atmospheric pressure

Answer 39

Force exerted by the weight of the atmosphere, at sea level 14.7psi

Question 40

Gauge pressure

Answer 40

Pressure that is measured that exceeds the atmospheric pressure

Question 41

Ambient pressure

Answer 41

Pressure that immediately surrounds an object

Question 42

Absolute pressure

Answer 42

Pressure that would be measured in a vaccuum

Question 43

Positive buoyancy

Answer 43

Buoyant force is more than the object weighs so the object floats

Question 44

Neutral buoyancy

Answer 44

Objects weight is equal to the weight of the fluid it displaces

Question 45

Negative bouyancy

Answer 45

The buoyant force is less than the object weighs, object sinks