Mechanics And Materials Flashcards
Define breaking stress
The maximum stress that an object can withstand before failure occurs
Define brittle
When an object will show very little strain before reaching its breaking stress
What is meant by the centre of mass?
The single point through which all the mass of an object can be said to act
What is meant by the conservation of energy?
Energy cannot be created or destroyed - it can only be transferred into different forms
What is meant by the 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
What is a couple?
Two equal and opposite parallel forces that act on an object through different lines of action. Causes 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
What is 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
What is an elastic collision?
A collision where the total kinetic energy of the system before the collision is equal to the total kinetic energy of the system after the collision ( kinetic energy is conserved )
What is meant by the 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
What is 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 resultant force and resultant moment acting on the object must be equal to zero
What is Hook’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
What is an impulse?
The change of momentum of an object when a force acts on it. Equal to the product of the force acting in the object and the length of time over which it acts
What is an inelastic collision?
A collision where the total kinetic energy of the system before the collision is not equal to the kinetic energy of the system after the collision (kinetic energy is not conserved)
What is meant by a moment?
The product of a force and the perpendicular distance from the line of action of the force to the pivot (a turning force)
What is Newton’s first law?
An object will remain in its current state of motion, unless acted on by a resultant force. An object requires a resultant force to accelerate
What is 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 ( F = ma )
What is Newton’s third law?
Every action has an equal and opposite reaction. If an object exerts a force on another object, then the other object must exert a force back, that is opposite in direction and equal in magnitude
What is 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
What is the principal 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 anti-clockwise moments acting about a point
What is a scalar quantity? Provide examples
A quantity that only has magnitude, no direction. Examples include length, mass, and temperature
What is the 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
What is tensile strain?
The ratio of an objects extension to its original length. It is a ratio of two lengths and so has no unit
What is tensile stress?
The amount of force acting per unit area. It’s unit is the Pascal (Pa)
What is meant by terminal speed?
The maximum speed of an object that occurs when the resistive and driving forces acting on the object are equal to one another
What is a vector quantity? Provide examples
A quantity with both direction and magnitude. Examples include velocity, displacement, and acceleration
Define Young’s modulus
The ratio of stress to strain for a given material. It’s unit is the Pascal (Pa)
