What did you learn last time?
• 1 thing you learnt from last lesson
• 1 question you had from last lesson that
wasn’t answered
• High 5
09 April 2015
Principle of moments
Objectives
Be able to define and use the
principle of moments
OUTCOMES
•
•
•
•
ALL
Be able to define the principle of moments
MOST
Be able to apply the principle of moments
to different situations
• SOME
• Be able to apply the principle of moments
to problems with more than 2 forces
Principle of Moments 
Total
anticlockwise
moment
=
Total clockwise
moment
Is this Balanced?
• Example 1 (of 3)
• Explain how you know if it is or not (using
maths to describe)
50 cm
90 cm
x cm
10 N
8N
Practical

Example 2 (of 3)
Take moments about the pivot to find the
distance x.
(system is obeying
20 N
principle of moments)
90 cm
50 cm
x cm
10 N
12 N
Example 3 (slightly harder)

Given that the system is balanced; take the clockwise
and anticlockwise moments about the pivot to find the
force X.
10N
5N
5cm
20cm
10N
extension
8N
60cm
5cm
5N
85cm
10cm
XN
Careful, Answer not
necessarily a whole
number
Summary
• Review vid:
http://www.youtube.com/watch?feature=pl
ayer_embedded&v=WclR1jR0kdk