1. Balanced Forces

2. Levers

3. Write out the statements that are true.
a The longer the lever, the bigger the force that is needed to move an object.
b It is easier to close a door if you push the door close to the hinge
c The shorter the lever, the bigger the force that is needed to move an object
d Joints are examples of pivots.
e Bones are examples of levers.

4. C, D and E

5. Learning Objective
To investigate, through practical experimentation, the principle of moments.

7. Recording your results
What do we need to record?
How many columns will we need in our table?

9. Recording your results

10. Weight and Mass YouTube - Eureka! Episode 7 - Weight vs. Mass
YouTube - Eureka! Episode 6 - Gravity
YouTube - Eureka! Episode 7 - Weight vs. Mass
Racing Balls

11. Write out each term along with its correct description
unbalanced system
moment
balanced system
Descriptions
anticlockwise moments = clockwise moments
two boys of different weights sit opposite each other on a see saw, both the same distance from the pivot
the turning effect of a force
Lever Principle
GCSE PHYSICS: Moments

12. Moment calculation pivot
Gina weighs 500 N and stands on one end of a seesaw. She is 0.5 m from the pivot.
What moment does she exert?
moment = 500 x 0.5
= 250 Nm
0.5 m
500 N
pivot

13. Moment equation f x d The moment of a force is given by the equation:
moment = force (N) x distance from pivot (cm or m)
moment f x d
Moments are measured in Newton centimetres (Ncm) or Newton metres (Nm).

14. Principle of moments The girl on the left exerts
an anti-clockwise moment,
which equals...
The girl on the right exerts a clockwise moment, which equals...
her weight x her distance
from pivot
her weight x her distance
from pivot

15. Principle of moments
If the anticlockwise moment and clockwise moment are equal then the see-saw is balanced. This is known as the principle of moments.
When something is balanced about a pivot:
total clockwise moment = total anticlockwise moment

16. Principle of moments – calculation
Two girls are sitting on opposite sides of on a see-saw. One girl weighs 200 N and is 1.5 m from the pivot. Where must her 150 N friend sit if the seesaw is to balance?
When the see-saw is balanced:
total clockwise moment = total anticlockwise moment
200 N x 1.5 m = 150 N x distance
200 x 1.5 = distance
150
distance of second girl = 2 m

17. Anagrams

18. Why don’t cranes fall over?
Tower cranes are essential at any major construction site.
load arm
trolley
counterweight
loading platform
tower
Concrete counterweights are fitted to the crane’s short arm. Why are these needed for lifting heavy loads?

19. Why don’t cranes fall over?
Using the principle of moments, when is the crane balanced?
3 m
6 m
10,000 N ?
moment of = moment of
load counterweight
If a 10,000 N counterweight is three metres from the tower, what weight can be lifted when the loading platform is six metres from the tower?

20. Why don’t cranes fall over?
moment of
load =
= ? x 6
load x distance of load from tower
moment of
counterweight
distance of counterweight from tower =
= 10,000 x 3
= 30,000 Nm
counterweight x
moment of load = moment of counterweight
? x 6 = 30,000
? = 3,000 6
? = 5,000 N

21. Crane operator activity
Where should the loading platform be on the loading arm to carry each load safely?