6. Moments

Question 1

What is a moment?

Answer 1

Turning effect around a pivot

Question 2

What is the equation involving moments?

Answer 2

M = Fdp

Moment = force x perpendicular distance from pivot

Moment unit is Nm

Question 3

What is the principal of moments?

Answer 3

Total clockwise moment = total anti-clockwise moment

Question 4

Explain what must happen to a counterweight on a tower to keep it balanced if a larger mass was placed on the loading platform?

Answer 4

• to make the anti clockwise and clockwise moments balanced, you should increase the weight/force of the counterweight ‘by increasing the counterweight’s mass of moving it further away from the pivot point
• both would increase the moment since moment = force x perpendicular distance

Question 5

What is centre of mass?

Answer 5

Point at which all of mass of an object could be said to act (avg position of mass)

Question 6

When does an object become unstable?

Answer 6

• when the line of action of the centre of mass passes beyond the edge of the object’s base

Question 7

How can the stability of an object be increased?

Answer 7

Increasing size of base
(Heavy base lowers centre of gravity)

Decreasing height

Decreases toppling angle

Question 8

Why does the upwards force at the right end of a plank of wood increase when object is moved towards that end?

Answer 8

• moments about left support
• as weight moves to right clockwise moment increases
• perp distance between weight + pivot increases
• anti-clockwise moment must increase to remain in equilibrium
• to increase the anti-clockwise moment right upwards force must increase