Mechanics Definitions Flashcards
Define the term ‘couple’
Two equal but opposite forces
State the principle of moments
When an object is in equilibrium the sum of the clockwise moments equals the sum of the anticlockwise moments
Define braking distance
The distance travelled by the car after the brakes are applied until the car stops
Define the torque of a couple
Torque = one of the forces x perpendicular distance between the forces
State hooke’s law
The extension is directly proportional to the force applied, as long as the elastic limit is not exceeded
x = kf
Define power
Power = work done / time
Define the youngster modulus of a material and state the condition when it applies
Young’s modulus = stress / strain
It is obeyed as long as you don’t exceed the elastic limit of the material
Define velocity
Velocity is the rate of change of displacement
Define centre of gravity
The point at which the entire weight of the body appears to act
Define the watt
1 joule (of work) per second
Define work done by a force
Force x distance moved in the direction of the force
Define moment of a force
Moment = force x perpendicular distance to the pivot
Define acceleration
Acceleration is the rate of change of velocity
Define the force constant of a spring
The force per unit extension of the spring
k = f/x
State the principle of conservation of energy
In a closed system, energy cannot be created or destroyed, only converted from one form to another.
Define density
Density = mass / volume
Define a material’s “elastic limit”
The material is permanently deformed when the force/stress is removed.
Explain what is meant by “plastic deformation”
The material is permanently deformed when the force / stress is removed
Define the ultimate tensile strength of a material
The maximum stress a material can withstand before braking
What does it mean to describe a material as brittle
A brittle material does not have a plastic region. It breaks at the elastic limit
Define the Newton
The force when a 1kg mass is accelerated at a rate of 1m/s^2
Write a word equation for the kinetic energy
Kinetic energy = 1/2 x mass x speed^2
Define thinking distance
The distance travelled by a driver from when the driver sees the problem and the brakes are applied.
Define a vector quantity and give one example
A quantity with both magnitude and direction.
Examples are: displacement, velocity, acceleration, force, weight
