4. Forces, density and pressure

Question 1

centre of gravity

Answer 1

weight of an object may be taken as acting at a single point known as centre of gravity.

D- the point where all the weight of the object is taken to act.

Question 2

moment of a force

Question 3

couple

Answer 3

pair of forces that acts to produce rotation only. equal in magnitude

Question 3

principle of moments

Answer 3

for a system in equilibrium, sum of clockwise moments about a point equals sum of anticlockwise moments about the same point.

Question 4

torque of a couple

Answer 4

Torque is the measure of force that can cause an object to rotate. force * diameter of circle

Question 5

equilibrium conditions and vector

Answer 5

resultant force in any direction is zero
resultant torque/moment about any point is zero

vector triangle to represent coplanar forces (coplanar- forces lying in same plane)

vector sum of forces acting is 0.
F1+F2+F3=0

Question 6

density

Answer 6

mass per unit volume

Question 7

pressure

Answer 7

force/area normal to the force

Question 8

upthrust

Answer 8

upthrust acting on an object in a fluid is due to a difference in hydrostatic pressure.

Question 9

derive formula of hydrostatic pressure

Answer 9

∆p = ρg∆h

Question 10

calculate upthrust acting on an object in a fluid

Answer 10

F = ρgV (Archimedes’ principle)