3.4 Mechanics and Materials Flashcards
Acceleration
change in V per unit t
Acceleration of free fall
Acceleration of an object only acted on by force of gravity
Braking distance
Distance travelled by vehicle in time taken to stop
Brittle
Snaps without bending or stretching when subject to stress
Centre of mass
Point through which a single force on the body has no turning affect
Couple
Pair of equal and opposite forces acting upon the same body but not along the same line
denisty
mass per unit volume for substance
displacement
distance in a given direction from equilibrium position
drag force
force of fluid resistance on an object moving through fluid
ductile
stretches easily without breaking
efficiency
ratio of useful energy transferred to energy supplied to it output power : input power
elastic limit
point beyond which wire is permanently stretched
elasticity
property of solid that allows it to regain shape after being deformed
equilibrium
State of an object when at rest or in uniform motion
friction
force opposing the motion of a surface that moves or tries to move across another surface
Hooke’s Law
the extension of a spring is proportional to the force applied to it
inertia
resistance of an object to a change of its motion
kinetic energy
energy of an object due to its motion
mass
measure of inertia of the motion of an object
moment
about a point is the force x perpendicular distance from the line of action of the force to the point
limit of proportionality
limit beyond which - if a wire or spring is stretched - the extension is no longer proportional to the force applied
Newton’s 1st Law of Motion
object remains at rest or in uniform motion unless acted upon by a resultant force
Newton’s 2nd Law of Motion
rate of change of momentum of an object is proportional to the resultant force applied to it
plastic deformation
deformation of a solid beyond the elastic limit
pressure
Force applied per unit area, perpendicular to the surface of an object.
conservation of energy
energy cannot be created or destroyed
principle of moments
object in equilibrium: sum of clockwise moments = sum of anticlockwise moments about a point
rest energy
energy due to rest mass - equal to mc^2
scalar
physical quantity with magnitude only
speed
change of distance per unit time
stiffness constant
force per unit extension needed to extend a wire or spring
stopping distance
thinking distance + braking distance
stopping potential
minimum pd applied to a metal plate to attract all the photoelectrons emitted from its surface back to the surface
strain
extension per unit length of a solid when deformed
stress
force per unit area of cross section in a solid perpendicular to cross section
useful energy
energy transferred to where it is wanted when its wanted
vector
physical quantity with magnitude and direction
velocity
change of displacement per unit time
weight
force of gravity acting on an object due to its mass
work
force x distance moved in the direction of the force
yield point
point at which the stress in a wire suddenly drops when the wire is subjected to increasing strain
Young’s Modulus
tensile stress (F/A) / tensile strain (∆L/L), assuming limit of proportionality has not been exceeded
projectile
projected object in motion acted on only by the force of gravity
conservation of momentum
for a system of interacting objects total momentum remains constant provided no external resultant force acts on the system
sublimation
change of state when a solid changes directly into a gas
elastic collision
total kinetic energy after the collision equals total kinetic energy before the collision
