Transcript Balanced Forces Levers Write out the statements that are true. • a The longer the lever, the bigger the force that is needed to.

Balanced Forces
Levers
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.
C, D and E
Learning Objective
To investigate, through
practical experimentation,
the principle of moments.
Recording your results
• What do we need to record?
• How many columns will we need in
our table?
Recording your results
Weight and Mass
YouTube - Eureka! Episode 6 Gravity
• YouTube - Eureka! Episode 7 - Weight vs.
Mass
Racing Balls
Write out each term along with its
correct description
unbalanced
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
Lever Principle
GCSE PHYSICS:
• the turning effect of a force
Moments
Moment calculation
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
Moment equation
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).
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
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
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
Anagrams
Why don’t cranes fall over?
Tower cranes are essential at any major construction site.
trolley
load arm
counterweight
loading platform
tower
Concrete counterweights are fitted to the crane’s short arm.
Why are these needed for lifting heavy loads?
Why
don’t
cranes
fall
over?
Using the principle of moments, when is the crane balanced?
3m
6m
?
moment of
load
10,000 N
=
moment of
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?
Why don’t cranes fall over?
moment of
load
= load x distance of load from tower
= ? x 6
moment of
= counterweight x distance of counterweight
counterweight
from tower
= 10,000 x 3
= 30,000 Nm
moment of load = moment of counterweight
? x 6 = 30,000
? = 3,000
6
? = 5,000 N
Crane operator activity
Where should the loading platform be on the loading arm
to carry each load safely?