Mechanics & Materials Flashcards
Acceleration
Change of velocity per unit time.
Acceleration of free fall
Acceleration of an object acted on only by the force of gravity.
Braking distance
The distance travelled by a vehicle in the time taken to stop it.
Breaking stress
Tensile stress needed to break a solid material.
Brittle
Snaps without stretching or bending when subject to stress.
Centre of mass
The centre of mass of the body is the point through which a single force on the body has no turning affect.
Conservation of momentum
For a system of interacting objects is the total momentum of the objects Remains constant provided no external resultant force acts on the system.
couple
pair of equal and opposite forces acting on a body but not along the same line.
density of a substance
mass per unit volume of the substance.
displacement
distance in a given direction.
dissipative forces
forces that transfer energy which is wasted.
drag force
the force of fluid resistance on an object moving through the fluid.
ductile
stretches easily without breaking.
efficiency
the ratio of useful energy transferred (or the useful work done) by a machine or device to the energy supplied to it.
Effort
the force applied to a machine to make it move
elastic collision
an elastic collision is one in which the total kinetic energy after the collision is equal to the total kinetic energy before the collision
elastic limit
point beyond which a wire is permanently stretched
elasticity
property of a solid that enables it to regain its shape after it has been deformed or distorted
energy
the capacity to do work
equilibrium
state of an object when at rest or in uniform motion
explosion
when two objects fly apart and the two objects carry away at opposite and equal momentums
force
rate of change of momentum(mass x acceleration for fixed mass).
free-body force diagram
a diagram of an object showing only the forces acting on the object.
friction
force opposing the motion of a surface that moves or tries to move across another surface.
fusion (thermal)
the fusing together of metals by melting them together.
gravitational force
an attractive force that acts equally on any two objects due to their mass.
Hooke’s law
the extension of a spring is proportional to the force needed to extend it up to a limit referred to as its limit of proportionality.
impulse
of a force acting on an object, force x time for which the force acts.
inertia
resistance of an object to change its motion.
Kinetic energy
The energy of a moving object due to its motion E=1/2mv^2
load
the force to be overcome by a machine when it shifts or raises an object
mass
measure of the inertia or resistance to a change of motion of an object
moment of a force about a point
force x perpendicular distance from the line of action of the force to the point (pivot)
momentum
mass x velocity, its unit is kgm/s
motive force
the force that drives a vehicle
Newton’s First Law of Motion
An object continues at rest or in uniform motion unless it is acted on by a resultant force
Newton’s Second Law of Motion
The rate of change of momentum of an object is proportional to the resultant force on it (resultant force = change in momentum/change in time)
Newton’s Third Law of Motion
When two objects interact, they exert equal and opposite forces on one another
Pascal
Unit of pressure or stress equal to 1 Nm^-2
Plastic Deformation
Deformation of a solid beyond its plastic limit
Potential Energy
The energy of an object due to its position
Power
Rate of transfer of energy= energy transferred/time taken
Pressure
The force per unit area that a gas or a liquid or a solid at rest exerts normally on (i.e. at right angles to) a surface. Pressure is measured in pascals (Pa), where 1 Pa=1 Nm-2
Principle of conservation of energy
in any change, the total amount of energy after the change is always equal to the total amount of energy before the change
Principle of conservation of momentum
when two or more bodies interact, the total momentum is unchanged, providing no external forces act on the bodies.
Principle of moments
for an object in equilibrium, the sum of the clockwise moments about any point= the sum of the anticlockwise moments about that point
Projectile
a projected object in motion acted on only by the force of gravity
scalar
physical quantity with magnitude only
speed
change in distance per unit time
stiffness constant
force per unit extension needed to extend a spring or wire
stopping distance
sum of the thinking and braking distances
strain
extension per unit length of a solid when deformed
stress
force per unit cross-sectional, perpendicular area in a solid
terminal speed
maximum speed reached by an object when the drag force on it is equal and opposite to the force causing the motion of the object
thinking distance
distance travelled by a vehicle in the time it takes the driver to react
Ultimate tensile stress
Tensile stress needed to break a solid material.
Useful energy
Energy transferred to where it is wanted when it is wanted.
Vector
A physical quantity with magnitude and direction.
Velocity
Change of displacement per unit time.
Weight
The force of gravity acting on an object.
Work done
Work is energy transferred by means of a force. Work = force x distance moved in the direction of the force. The work done W by a force F when its point of application moves through displacement s at angle (theta) to the direction of the force is given by W = Fs cos (theta).
yield point
point at which the stress in a wire suddenly drops when the wire is subjected to increasing strain
Young modulus
tensile stress/strain (assuming the limit of proportionality has not been exceeded). The unit of the Young modulus is the pascal (Pa) which is equal to 1 N/m2
