Mechanics Flashcards
(26 cards)
What are vector and scalar quantities?
A vector quantity is any physical quantity that has both magnitude and direction, scalar quantities only have magnitude
Define the moment of a force
moment of a force = the force multiplied by the perpendicular distance from the line of action of the force to the pivot
Define a couple
A pair of forces equal in magnitude, opposite in direction which are separated by a perpendicular distance. (moment of a couple = force x perp distance between the forces)
Define Centre of Mass
The centre of mass of an object is defined as the point in a body where the whole weight appear to act
State the principle of moments
for a body in equilibrium, the sum of the clockwise moments is equal to the sum of the anti clockwise moments about a point
What is friction?
A force that opposes motion, contact friction is between solid surfaces, drag or fluid friction is a resistance experienced due to collisions with the molecules of the fluid
Newtons first law
An object will remain at rest or continue moving at a constant velocity unless acted upon by an unbalanced force
Define Inertia
The mass of a body is a measure of its inertia which is its resistance to change in its motion
Newtons second law
The rate of change of momentum of an object is proportional to the resultant force on the object, and in the direction of the resultant force
Newtons third law
When body A exerts a force on body B, body B exerts an equal and opposite force on body A
Define linear momentum
The momentum of an object is defined as the product of mass and velocity
Define impulse
The impulse of a force is the product of the force and the time for which the force acts
What is the principle of conservation of momentum?
Within a closed system (where bo external forces apply) the total momentum in any specified direction remains constant
Define an elastic collision
A collision in which the total kinetic energy is conserved
Define an inelastic collision
A collision in which some or all of the kinetic energy is transferred to other forms, for example, heat and sound energy
Define energy
Energy is the capacity to do work
State the principle of conservation of energy
Energy cannot be created or destroyed only transferred
Define power
Power is the rate of doing work or rate of energy transfer
Define density
Density is the mass per unit volume of a substance
State Hookes law
The extension is directly proportional to the force applied provided the elastic limit is not exceeded
Define tensile stress
the tensile force per unit cross sectional area
Define tensile strain
the ratio of extension to original length
Define young modulus
The ratio of stress to strain and is constant for a specific material
Describe a ductile material
Can be drawn out into wires or battered into sheets, show large plastic deformation - copper, gold, iron
