Stress, Strain and Work Done Definitions

Define elastic deformation:

Deformation that is not permanent. When the force producing the deformation is removed the object will return to its original shape

Define plastic deformation:

Deformation that is permanent. When the force producing the deformation is removed the object will not fully return to its original shape

Define efficiency:

Efficiency = useful energy output / total energy input x 100%. It is also equal to useful power output / total power input x 100%

Define the principle of the conservation of energy:

Energy can not be created or destroyed, only transformed from one form to another

Define kinetic energy:

The energy an object has due to its motion. KE = 1/2mv^2

Define gravitational potential energy:

The energy an object has due to its position in a gravitational field. GPE = mgh

Define the Young Modulus:

Young Modulus is equal to stress / strain for an object. It is analogous to the stiffness, k, of a spring and is only dependent on the material the object is made from

Define thinking distance:

The distance a car travels between the driver first registering a hazard and the brakes being applied

Define the watt:

1 watt of power is transferred when 1J of work is done in a time of 1s

Define brittle:

A brittle material will break when subjected to stress without significant strain occurring. Brittle materials will also tend to fracture before plastic deformation occurs

Define deformation:

A deformation is any change of the dimensions of an object from its original shape.

Define fluid:

A liquid or a gas

Define polymeric:

A polymeric material is made of polymers. Polymeric materials tend to have more complicated stress-strain curves, often with two different regimes corresponding to the unfurling of polymer chains followed by the stretching of the straightened chains

Define trilateration:

A technique used to determine the position of an object using a minimum of 3 satellites and timing signals as reference

Define ductile:

Any material that is easy to draw out into a wire. Metals are good examples of ductile materials

Define braking distance:

The distance a car travels between the brakes being applied and the car coming to a complete stop. The car is decelerating during this time

Define compressive:

Relating to a deformation which tends to squash (decrease the length) of an object

Define tensile:

Relating to a deformation which tends to stretch (increase the length) of an object

Define Hooke's Law:

The extension of a spring is directly proportional to the force applied to it (within the elastic limit). F = kx, where k is the spring constant ('stiffness' of the spring in N/kg)

Define strain:

The extension of an object / its original length. If the object has been compressed the strain will be negative

Define weight:

The force a massive object experiences due to gravity. It is equal to the object's mass x gravitational field strength

Define stress:

The force applied to an object divided by its cross-sectional area. It can be tensile (tending to stretch) or compressive (tending to squash)

Define drag:

The force experienced by an object moving through a field

Define pressure:

The force per unit area

Define work done:

The magnitude of the force multiplied by the distance moved in the direction of the force (when work is done, energy is transferred)

Define density:

The mass per unit volume of an object

Define ultimate tensile stress:

The maximum stress an object can endure before fracture will occur

Define terminal velocity:

The maximum velocity an object reaches when falling through a fluid, it occurs when drag becomes equal to weight

Define centre of gravity:

The point at which the entire weight of an object can be regarded as acting

Define power:

The rate of doing work. Power = work done / time = energy transferred / time

Define spring constant:

The ratio of force applied to extension for a spring. The higher the stiffness, the less the spring will extend for a given force

Define elastic limit:

The regime under which elastic deformation occurs. Beyond this point the deformation will be plastic. (For springs, Hooke's Law applies within the elastic limit of the spring)

Define stopping distance:

The sum of the thinking distance and braking distance

Define moment of a force:

The turning effect of an individual force. Equal to the magnitude of the force multiplied by the perpendicular distance between the line of action of the force and the point about which moments are being taken

Define the newton:

The unit of force. The resultant force on a 1kg object if it is accelerating at 1m/s^2

Define the joule:

The unit of work. 1 joule of work is done when a force of 1N moves through a distance of 1m

Define couple:

Two forces of equal magnitude pointing in opposite directions with their lines of action not colinear. They thus tend only to produce rotation