4. Mechanics And Materials Definitions Flashcards
Define breaking stress
The maximum stress that an object can withstand before failure occurs
Define brittle
A brittle object will show very little strain before reaching its breaking point
Define centre of mass
The single point though which all the mass of an object can be said to act
Define conservation of energy
Energy cannot be created or destroyed- it can only be transferred into different forms
Define conservation of momentum
The total momentum of a system before an event must be equal to the total momentum of the system after the event, assuming no external forces act.
Define couple
Two equal and opposite parallel force that act on object through different lines of action. It has the effect of causing a rotation without translation.
Define density
The mass per unit volume of a material
Define efficiency
The ratio of useful output to total input for a given system
Define elastic behaviour
If a material deforms with elastic behaviour, it will return to its original shape when the deforming forces are removed. The object will not be permanently deformed.
Define elastic collision
A collision in which the total kinetic energy of the system before the collision is equal to the total kinetic energy of the system after the collision
Define elastic limit
The force beyond which an object will no longer deform elastically and instead deform plastically. Beyond the elastic limit, when the deforming forces are removed, the object will not return to its original shape.
Define elastic strain energy
The energy stored in an object when it is stretched. It is equal to the work done to stretch the object and can be determined from the area under a force-extension graph.
Define equilibrium
For an object to be in equilibrium, both the resulting force and resultant moment acting on the object must be equal to zero.
Define Hooke’s Law
The extension of an elastic object will be directly proportional to the force applied to it up to the object’s limit of proportionality
Define impulse
The change of momentum of an object when a force acts on it. It is equal to the product of the force acting on the object and the length of time over which it acts
Define inelastic collision
A collision in which the total kinetic energy is the system before the collision is not equal to the kinetic energy of the system after the collision
Define moment
The product of a force and the perpendicular distance from the line of action of the force to the pivot
Define momentum
The product of an object’s mass and velocity
Define Newton’s first law
An object will remain it its current state of motion, unless acted on by a resultant force. An object requires a resultant force to be able to accelerate
Define Newton’s second law
The sum of the forces acting on an object is equal to the rate of change of momentum of the object
Define Newton’s third law
Every action has an equal and opposite reaction. If an object exerts a force on another object, the the other object must extend a force back, that is opposite in direction and equal in magnitude.
Define plastic behaviour
If a material deforms with plastic behaviour, it will not return to its original shape when the deforming forces are removed. The object will be permanently deformed.
Define the principle of moments
For an object to be in equilibrium, the sum of the clockwise moments acting about a point must be equal to the sum of the anticlockwise moments acting about the point.
Define scalar
A scalar quantity is one that only has a magnitude. Examples include length, mass and temperature.
Define spring constant
The constant of proportionality for the extension of a spring under a force. The higher the spring constant, the greater the force needed to achieve a given extension.
Define stiffness
A measure of how difficult it is to stretch a given object
Define tensile strength
The ratio of an object’s extension to its original length. It is a ratio of two lengths and so has no unit.
Define tensile stress
The amount of force acting per unit area. Its unit it the pascal (Pa)
Define terminal speed
The maximum speed of an object that occurs when the resistive and driving forces acting on the object are equal to each other.
Define vector
A vector quantity is one that has both a magnitude and a direction. Examples include velocity, displacement and acceleration.
Define Young modulus
The ratio of stress to strain for a given material. Its unit is the Pascal (Pa).
