5 — moments

Question 1

Principle of moment

Answer 1

Principal of moment states that when an object is in equilibrium, sum of clockwise moments about a pivot is equal to the sum of anti-clockwise moments abt the same pivot.

Question 2

Moments

Answer 2

Moments is the product of a force F and the perpendicular distance d from the pivot to line of action of force.

Question 3

Centre of gravity

Answer 3

Centre of gravity is an imaginary point where the entire weight of the object seems to act

Question 4

Stability

Answer 4

Stability of an object is the measure of its ability to return to its original position after it is slightly displaced

Question 5

How to increase stability

Answer 5

Lowering centre of gravity
Increasing base area

Question 6

Moments Answ formula

Answer 6

Centre of gravity rises/lowered -> line of action of weight falls outside/within base area -> produces anti-/clockwise moment about pivot -> object topples/ back to original position.

Question 7

What happens when perpendicular distance of line of action to pivot = 0?

Answer 7

No moments about the pivot.

Question 8

How to result in the largest moment about a pivot?

Answer 8

By moments = F x perpendicular distance, Max. Perpendicular distance of line of action to pivot.

Question 9

Explain why the sheet stops when line of action of weight is below the pivot point A.

Answer 9

Since the perpendicular distance betw G and pivot A = 0m, moment about pivot = 0.

Question 10

How to determine the centre of gravity of an irregular figure

Answer 10

1. Make 3 holes X Y and Z at diff positions on the lamina
2. Hang the lamina thru hole X on a pin clamped horizontally. When the lamina comes to rest, its centre of gravity is vertically below pivot X.
3. Tie a plumb line to the pin and mark the line XP on the lamina.
4. Repeat step 3 to points y and Z
5. The point of intersection of XP YP and ZP is the cog of the lamina.

Question 11

The front of the helicopter is tilting down, centre of gravity of the helicopter stays the same height. State how the lift forces from the roots are adjusted to achieve this effect. [1]

Answer 11

The lift force from back rotor is increased and the lift force from the front rotor is decreased. This results in an increase in anticlockwise moment, causing the helicopter to tilt forward.