4.0 Mechanics And Materials Flashcards
What is a vector quantity
It has both magnitude and direction
What is a scalar quantity
It has only magnitude and no direction
What are some examples of vector quantities
displacement, velocity, force
What are some examples of scalar quantities
distance, speed, energy
how are vectors drawn
arrows representing their magnitude and direction
how are vectors added
by resolving into components or drawing a vector triangle
Conditions for multiple forces acting on a point
resultant must be zero for equilibrium
Define a moment
force × perpendicular distance between pivot and the line of action of the force
Define a couple
A pair of equal and opposite coplaner forces
Define the moment of a couple
force × perpendicular distance between lines of action of the forces
state the principle of moments
Sum of the anticlockwise moments = sum of the clockwise moments
Define the centre of mass
The point from where all the mass of an object appears to be concentrated
Where is the centre of mass of a uniform solid
in the centre of the object
Calculations of averages
Total value / total time
Characteristics of displacement - time graphs
gradient = velocity
Characteristics of velocity - time graphs
area = displacement
gradient = acceleration
Characteristics of acceleration - time graphs
area = velocity
Relationship between horizontal components and vertical components in projectile motion
They are independent of each other
Define friction
A resistive, contact force that opposes the relative motion of two surfaces
Define lift
A force that acts perpendicular to the direction of motion of an object moving through a fluid
Define drag
A resistive force that acts parallel and opposite to the direction of motion of an object moving through a fluid
Define terminal velocity
Terminal velocity is the constant velocity that an object reaches when the resistive force acting on it equals the driving force
relationship between air resistance and speed
Air resistance increases with speed
Factors affecting maximum speed of a vehicle
shape, size, power
Define Newtons first law of motion
An object will remain at rest or in constant straight line motion unless acted on by an external force
Define Newtons second law of motion
The rate of change of the velocity is directly proportional to the force acting on it and inversely proportional to the mass
Define Newtons third law of motion
If object A exerts a force on object B, then object B will exert an equal and opposite force on object A
Define momentum
mass × velocity
What must be conserved in all collisions
Momentum
What is force
The rate of change of momentum
Define impulse
The change in momentum
Significance of area of a force-time
The impulse
Define an elastic collision
momentum and kinetic energy conserved
Define an inelastic collision
kinetic energy not conserved
Define an explosions
The opposite to an inelastic collision, where energy is converted to kinetic energy
Momentum conservation in transport design
crumple zones, air bags, and seat belts increase the time of impact, resulting in reduced forces on the passengers
Define work done
Energy transferred
Define power
The rate of energy transfer
Area under force-displacement graphs
Work done
What must always be conserved
Energy
Define density
The mass per unit volume
Define Hooke’s law
Force is directly proportional to extension up until the elastic limit
Define the elastic limit
The maximum force or extension that a material can withstand while still returning to its original shape when the force is removed
Define tensile strain
Tensile strain is the ratio of the extension of a material to its original length
Define tensile stress
Tensile stress is the force applied per unit cross-sectional area of a material
Define elastic strain energy
The energy stored in a material when it is deformed elastically
Define breaking stress
The maximum stress a material can withstand before it fractures or breaks
Define plastic behaviour
It occurs when a material is stretched beyond its elastic limit, causing permanent deformation
How is plastic behaviour shown on a force-extension graph?
Beyond the elastic limit, the graph curves, indicating that the material is undergoing plastic deformation
What is brittle behaviour?
Brittle behaviour occurs when a material fractures with little or no plastic deformation
How is brittle behaviour shown on a force-extension graph?
There is no noticeable curve or plastic deformation before fracture
What happens to energy during deformation within the elastic limit?
When a material deforms within its elastic limit, work is done, this energy is stored as elastic strain energy. The material returns to its original shape when the force is removed, conserving the energy
Define young’s modulus
A measure of a material’s stiffness. The ratio of tensile stress to tensile strain within elastic limit.
