FRICTION

Question 1

Tangential forces generated between contacting surfaces
are called _______ ________ and occur to some degree in the
interaction between all real surfaces.

Answer 1

friction forces

Question 2

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.

Answer 2

oppose

Question 3

_________ _________are present throughout nature and exist in
all machines no matter how accurately constructed or carefully
lubricated.

Answer 3

Friction forces

Question 4

A machine or process in which friction is small
enough to be neglected is said to be _______.

Answer 4

ideal

Question 5

When friction must
be taken into account, the machine or process is termed _______.

Answer 5

real

Question 6

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 ______.

Answer 6

heat

Question 7

______ is another effect of friction.

Answer 7

Wear

Question 8

A contact resistance exerted by one body to another.

Answer 8

Friction

Question 9

Give the 3 types of friction.

Answer 9

1. Dry Friction
2. Fluid Friction
3. Internal Friction

Question 10

Give the 2 kinds/regimes of dry friction

Answer 10

1. Static friction’ (“stiction”) between non-moving surfaces.
2. Kinetic friction (sometimes called sliding friction or dynamic friction) between moving surfaces.

Question 11

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.

Answer 11

Dry Friction

Question 12

Dry Friction is also called what?

Answer 12

Coulomb friction

Question 13

The principles of dry or Coulomb friction were developed
largely from the experiments of Coulomb in ______ and from
the work of Morin from ______ to ______ .

Answer 13

1781, 1831, 1834

Question 14

It is the point of slippage

Answer 14

impending motion

Question 15

The region up to the point of slippage or
impending motion is called the range of ________ _________

Answer 15

static friction

Question 16

The value of the friction force is determined by the equations of
____________.

Answer 16

equilibrium (∑Fx = 0, ∑Fy = 0)

Question 17

True or False?

Static friction force may have any value from zero up to and
including the maximum value.

Answer 17

True

Question 18

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.

Answer 18

True

Question 19

Formula for Static Friction

This equation applies only to cases where motion is impending with the friction force at its peak value.

Answer 19

Fmax= μs x N

where μs is the proportionality constant, called the coefficient of static friction.

Question 20

For a condition of static equilibrium when motion is not impending, the static friction force is:

Answer 20

F < μs x N

Question 21

After slippage occurs, a condition of _______ friction
accompanies the ensuing motion.

Answer 21

kinetic

Question 22

True or False?

Kinetic friction force is usually
somewhat less than the maximum static friction force.

Answer 22

True

Question 23

True or False?

The kinetic friction force Fk is also proportional to the normal force.

Answer 23

True

Question 24

Formula for Kinetuc Friction

Answer 24

Fmax= μk x N

where μk is the coefficient of kinetic friction. It follows that μk is generally less than μs.

Question 25

The direction of the resultant R in figure b measured
from the direction of N is specified by what equation?

Answer 25

tan a = F/N or tan ∅ = μ,

Question 26

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.

Answer 26

Fluid Friction

Question 27

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.

Answer 27

Internal Friction