Statics - Definitions Flashcards
Force
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)
Moment
A moment is the turning effect of a force
Units of Nm
Couple
A pair of equal forces acting in opposite directions around a central turning point
Scalar quantity
A quantity that has no direction
Vector quantity
These are things that have magnitude and direction and act in a straight line direction
Resultant force
The effect of two or more vectors. The sum of the vectors is known as the resultant
Centre of gravity
Is the point about which a body is perfectly balanced
There is only one centre of gravity
Tensile
Pulling apart
Compression
Squashing
Torsion
Twisting
Shear
Pulling/slicing two layers/bodies apart
Hooke’s law
The amount of force is doubled, the amount of extension is doubled
(Extension is directly proportional to force)
Stress
The magnitude of forces that cause deformation, always accompanied by strain
Strain
The deformation of a material due to stress
Young’s modulus
The ratio of stress and strain
Bulk modulus
This gives the change of volume of a solid substance as the pressure is changed
Poisson’s ratio
The ratio of transverse strain to axial strain in a stressed member
Transverse strain - diameter decrease
Axial strain - length increase
Hardness
High resistance to indentation or any action to penetrate the surface. Eg, diamond
Toughness
The ability to resist breakage when deforming or impact forces are applied to it.
Brittleness
Break with little or no change of shape eg glass, cast iron and very hard steel
Ductility
Can be stretched into new shapes without breaking apart, will keep their new shape after being stretched, eg wire and copper
Plasticity
A material that can be readily forced into a different shape permanently without fracturing. Eg putty in a window frame
Elasticity
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
Elastic limit
The maximum distorting force that can be applied to the solid without causing permanent distortion
Fluid
Anything that can flow, liquids gasses and vapours
Vapours
A gas that can be liquified by an increase in pressure without decreasing its temperature.
Volatile
This is a liquid that evaporates (vaporises) at normal temperature
Eg, petrol, methylated spirits and alcohol
Flammable/inflammable
A material that will catch fire easily, eg. Most fuels, light oils and some paints
Flash point
The temperature something has to be at before it will catch fire when exposed to a naked flame, aviation fuel: 38°C
Toxicity
Refers to how poisonous a substance is.
Inert
A substance that will not chemically combine with other substances eg, neon, argon, and helium
Bouyancy
The ability of an object to float
Archimedes principal
This states that when an object is submerged in a liquid, the object displaces the same volume of water as its volume
Buoyant force
The force that a submerged object is held up by, it is equal to the weight of the water being displaced
Principle of moments
For an object to balance horizontally the opposing moments must be equal in magnitude
Datum
Imaginary line from which all horizontal measurements are taken usually for balance purposes
Tension
Stress that is applied causing an increase in the length of a body, known also as tensile stress or axial or normal stress
Strength
Tendency to withstand an applied load without failure or plastic deformation
Malleability
Tendency to undergo compression without damage malleable materials can be beaten rolled or pressed
Pressure
Force applied to the surface of an object, measured in bar, millibar or hectoPascals
Atmospheric pressure
Force exerted by the weight of the atmosphere, at sea level 14.7psi
Gauge pressure
Pressure that is measured that exceeds the atmospheric pressure
Ambient pressure
Pressure that immediately surrounds an object
Absolute pressure
Pressure that would be measured in a vaccuum
Positive buoyancy
Buoyant force is more than the object weighs so the object floats
Neutral buoyancy
Objects weight is equal to the weight of the fluid it displaces
Negative bouyancy
The buoyant force is less than the object weighs, object sinks
