AS FEM Definitions Flashcards
Explain the term systematic error
Systematic errors in measurements are errors which show
A pattern
A bias
Or a trend
State what is meant by a scalar quantity
A scalar quantity is a quantity that has magnitude only
State two examples of scalar quantities
Met
Mass
Energy
Temperature
State example of a vector quantity ( other than force )
Velocity
Acceleration
Momentum
State the difference between a scalar quantity and a vector quantity
A vector quantity has direction (as well as magnitude) and a scalar quantity does not
Explain what is meant by the spring constant k of a spring
K= force/ extension
State the principle of moments
For a system in equilibrium, the sum of the ACW moments = sum of CW moments
About any given point
State the principle of
Conservation of momentum
The resultant momentum of a system is constant before and after a collision, provided no external forces act
The total momentum of a system is the same before and after an interaction in an isolated system
State 2 relationships between the forces that must be satisfied
if an object is to remain in equilibrium
The resultant force acting on an object = 0
And
The CW and ACE moments must be equal, or the resultant torque is 0
Define the moment of a force
The product of
The force
And
The perpendicular distance from the line of action of the force to the pivot
Explain what is meant by the centre of gravity
The point (in a body) at which the weight (or gravitational force) of an object appears to act
State 2 conditions that must be satisfied for the rod to be in equilibrium
Resultant force =0
And
Resultant torque = 0 at any point
What is meant by
tensile stress
Tension\ area
Or
Force/ area (perpendicular to the surface at which the force acts)
Tensile strain
Extension / original length
Elastic limit
The point, stress, strain, force/ extension up to which
Either - all energy sustained to stretch is returned when the deformed force is removed
Or- the shape returns to its original form when the deforming force is removed
Or- beyond such strength causes plastic deformation or permanent deformation
Yield stress of a material
The force per unit area
At which a material is extended
Considerably, a lot, plastically
Define the young modulus for a material
Young modulus=
Tensile stress/ tensile strain
Define the density of a material
Density =
Volume
State hooke’s law for a material in the form of a wire
The extension is proportional to the applied force up to the limit of proportionality
Define young modulus of a material with units it is measured in
(2)
Ratio of tensile stress to tensile strain
Pa
/
Nm -2
Constant k of a spring
And unit of k
K= force/ extension
Measured in Nm -1
State the formula for principle of conservation of momentum
E mv = 0
Where mv is momentum
E as in sum of
Inelastic collision
Kinetic energy is not conserved
How the force acting on a body
Is related to the change in momentum of the body
Force= rate of change of momentum
Newton’s first law of motion
Objects either stay at rest or moves with constant velocity unless acted on by a force
Ratio of acceleration force to weight
F over mg
