FRICTION Flashcards
Tangential forces generated between contacting surfaces
are called _______ ________ and occur to some degree in the
interaction between all real surfaces.
friction forces
Whenever a tendency
exists for one contacting surface to slide along another surface,
the friction forces developed are always in a direction to ________
this tendency.
oppose
_________ _________are present throughout nature and exist in
all machines no matter how accurately constructed or carefully
lubricated.
Friction forces
A machine or process in which friction is small
enough to be neglected is said to be _______.
ideal
When friction must
be taken into account, the machine or process is termed _______.
real
In
all cases where there is sliding motion between parts, the
friction forces result in a loss of energy which is dissipated in the
form of ______.
heat
______ is another effect of friction.
Wear
A contact resistance exerted by one body to another.
Friction
Give the 3 types of friction.
- Dry Friction
- Fluid Friction
- Internal Friction
Give the 2 kinds/regimes of dry friction
- Static friction’ (“stiction”) between non-moving surfaces.
- Kinetic friction (sometimes called sliding friction or dynamic friction) between moving surfaces.
A type of friction that occurs when the unlubricated surfaces of two solids
are in contact under a condition of sliding or a tendency to
slide.
Dry Friction
Dry Friction is also called what?
Coulomb friction
The principles of dry or Coulomb friction were developed
largely from the experiments of Coulomb in ______ and from
the work of Morin from ______ to ______ .
1781, 1831, 1834
It is the point of slippage
impending motion
The region up to the point of slippage or
impending motion is called the range of ________ _________
static friction
The value of the friction force is determined by the equations of
____________.
equilibrium (∑Fx = 0, ∑Fy = 0)
True or False?
Static friction force may have any value from zero up to and
including the maximum value.
True
True or False?
For a given pair of mating surfaces the
experiment shows that this maximum value of static friction Fmax is
proportional to the normal force N.
True
Formula for Static Friction
This equation applies only to cases where motion is impending with the friction force at its peak value.
Fmax= μs x N
where μs is the proportionality constant, called the coefficient of static friction.
For a condition of static equilibrium when motion is not impending, the static friction force is:
F < μs x N
After slippage occurs, a condition of _______ friction
accompanies the ensuing motion.
kinetic
True or False?
Kinetic friction force is usually
somewhat less than the maximum static friction force.
True
True or False?
The kinetic friction force Fk is also proportional to the normal force.
True
Formula for Kinetuc Friction
Fmax= μk x N
where μk is the coefficient of kinetic friction. It follows that μk is generally less than μs.
The direction of the resultant R in figure b measured
from the direction of N is specified by what equation?
tan a = F/N or tan ∅ = μ,
A type of friction that occurs when adjacent layers in a fluid (liquid or gas) are moving at different velocities. This motion causes frictional forces between fluid elements, and these forces depend on the relative velocity between layers. When there is no relative velocity, there is no fluid friction. Fluid friction depends not only on the velocity gradients within the fluid but also on the viscosity of the fluid, which is a measure of its resistance to shearing action between fluid layers.
Fluid Friction
A type of friction that occurs in all solid materials which are subjected to cyclical loading. For highly elastic materials the recovery from deformation occurs with very little loss of energy due to internal friction. For materials which have low limits of elasticity and which undergo appreciable plastic deformation during loading, a considerable amount of internal friction may accompany this deformation. The mechanism of internal friction is associated with the action of shear deformation, which is references on materials science.
Internal Friction
