Module 2

Question 1

friction

Answer 1

force opp to the direction in which the body moves or tends to move is developed at contact surfaces

Question 2

main cause of friction

Answer 2

surface roughness

Question 3

limiting friction

Answer 3

max value of friction

Question 4

coefficient of friction

Answer 4

constant of proportionality

Question 5

coeff of static friction

Answer 5

coeff of friction when the body is at rest

Question 6

coeff of dynamic/kinetic friction

Answer 6

cof when body is in motion

Question 7

angle of friction

Answer 7

angle between normal reaction at the contact surface and resultant of normal reaction and limiting friction

Question 8

angle of repose

Answer 8

max inclination of a plane on which a body can remain at rest, without applying external force

Question 9

dry friction / Coulomb friction

Answer 9

when unlubricated surfaces of 2 bodies in contact slides or tends to slide, the res friction

Question 10

Coulomb’s laws of friction

Answer 10

1) the max friction that can be developed is independent of area of contact
2) at low velocity the frictional force is independent of velocity of contact surface
3) the max friction is proportional to the normal reaction at the contact surface

4) friction always acts in a direction opposite to the direction in which the body moves or tends to move
5) till the limiting value is reached, the magnitude of friction is eq to the ext force which moves the body
6) the force of friction depends on roughness of the surfaces in contact. when perfectly smooth, friction is 0

Question 11

parallel forces

Answer 11

forces whose lines of action are parallel to each other

Question 12

couple forces

Answer 12

2 forces having the same magnitude, parallel line of action and opposite sense are said to form a couple

Question 13

arm of couple

Answer 13

the distance between line of action of couple forces

Question 14

properties of force couple

Answer 14

1) 2 couple Fs are equal in magnitude and opp in dirn, so sum of forces is 0
2) the moment at abt any point in the plane is constant and independent of the position of the moment centre
3) action of couple on rigid body will not be changed if the arm is turned in the plane of couple through any angle about one of its ends

Question 15

beam

Answer 15

structural element which has 1 dimension considerably larger than other 2 dimensions and offers R to bending due to applied loads