Forces, Density & Pressure

Question 1

Define upthrust

Answer 1

A force experienced by an object immersed in a fluid due to pressure difference between the top and bottom of the object.

Question 2

Define centre of gravity

Answer 2

It is the point where all the weight of an object maybe considered to act.

Question 3

Define Drag/viscous force

Answer 3

It is similar to friction. When an object moves through a fluid, there is a friction between it and the fluid.

Question 4

Centre of gravity

Answer 4

It is the point where all the weight of an object may be considered to act

Question 5

Define moment of a force

Answer 5

Force × perpendicular distance of the line of action of the force from the pivot
F × dsin∅

Question 6

State the principle of moments

Answer 6

For any object, that is in equilibrium, the sum of clockwise moments about any pivot provided by the forces acting on the object equals the sum of anticlockwise moments about the same pivotal point.

Question 7

Define Torque

Answer 7

Total moment of a system
Unit = Nm
It is a vector

Question 8

Define Couple

Answer 8

Two forces are said to be a couple of they are
• Equal in magnitude
• Parallel, but in opposite direction
• Must be separated by a distance

Question 9

Define torque of a couple

Answer 9

One of the forces × separation between them
Torque = Fd1 + Fd2

Question 10

State the principles of an equilibrium

Answer 10

For an object to be in equilibrium, two conditions must be met:
1) Resultant forces that act on the object is zero (in any direction)
2) Resultant moment is zero (about any point)

Question 11

Define Density

Answer 11

Mass per unit volume

Question 12

Define pressure

Answer 12

Force per unit area of cross-section
P= F/A
Unit:- Pa or Nm