Chap 4: Forces

Question 1

Hooke’s law:

Answer 1

Within the limit of proportionality the extension produced in a material is directly proportional to the force applied.

Question 2

● Centre of gravity (of a body):

Answer 2

The point at which the whole weight of the body appears to act.

Question 3

● Moment of a force (about a pivot):

Answer 3

Product of the force and the perpendicular distance from the line of action of the force to the pivot.

Question 4

● Couple:

Answer 4

A pair of forces acting on the same body that are equal in magnitude but opposite in direction and produce rotation only.

Question 5

● Torque of a couple:

Answer 5

The turning effect of a couple is equal to the product of one of the forces of the couple and the perpendicular distance between the lines of action of the forces

Question 6

Principle of Moments: For a body in rotational equilibrium

Answer 6

the sum of clockwise moments about any axis of rotation (or pivot) must be equal to the sum of anti-clockwise moments about the same axis (or pivot).

Question 7

Define Upthrust :

Answer 7

Upthrust is equal in magnitude and opposite in direction to the weight of the fluid displaced by a submerged or floating object.

Question 8

● Principle of flotation:

Answer 8

F an object floating in equilibrium the upthrust is equal in magnitude and opposite in direction to the weight of the object.