Lesson 9

Question 1

generated between contacting surfaces
are called friction forces

Answer 1

Tangential 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__________ which is dissipated in the form of heat.

Answer 6

loss of energy

Question 7

is another effect of friction.

Answer 7

wear

Question 8

occurs when the unlubricated surfaces of two solids are in contact under a condition of sliding or a tendency to slide.

Answer 8

Dry Friction

Question 9

Dry Friction is also called___________

Answer 9

Coulomb friction

Question 10

motion. This type of friction is also called Coulomb friction. The principles of dry or Coulomb friction were developed largely from the experiments of Coulomb in

Answer 10

1781 and from the work of Morin from 1831 to 1834.

Question 11

Static friction has___________.

Answer 11

no motion

Question 12

Kinetic friction has_________.

Answer 12

motion

Question 13

the point of slippage or impending motion is called the range of static friction, and in this range the value of the friction force is determined by the________________.

Answer 13

equations of equilibrium

Question 14

Static Friction equation describes only the
____________________of the static friction force and not any lesser value.

Answer 14

limiting or maximum value

Question 15

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

Answer 15

Kinetic friction

Question 16

The direction of the resultant R measured from the direction of N is specified by tan 𝛼 = 𝐹/𝑁.

Answer 16

Friction Angles

Question 17

occurs when adjacent layers in a fluid (liquid or gas) are moving at different velocities.

Answer 17

Fluid Friction

Question 18

When there is no__________ there is no fluid friction.

Answer 18

relative velocity

Question 19

Fluid friction depends not only on the velocity gradients within the fluid but also on the__________.

Answer 19

viscosity of the fluid

Question 20

occurs in all solid materials which are subjected to cyclical loading.

Answer 20

Internal Friction

Question 21

For ______________ materials the recovery
from deformation occurs with very little loss of energy due to internal friction.

Answer 21

highly elastic

Question 22

The mechanism of internal friction is associated with the _______________, which is references on materials science

Answer 22

action of shear deformation