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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

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Presentation Transcript
write out the statements that are true
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.
learning objective
Learning Objective

To investigate, through practical experimentation, the principle of moments.

recording your results
Recording your results
  • What do we need to record?
  • How many columns will we need in our table?
weight and mass
Weight and Mass
  • YouTube - Eureka! Episode 7 - Weight vs. Mass

YouTube - Eureka! Episode 6 - Gravity

Racing Balls

write out each term along with its correct description
Write out each term along with its correct description

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

unbalanced system

moment

balanced system

Lever Principle

GCSE PHYSICS: Moments

moment calculation
Moment calculation

0.5m

500N

pivot

Gina weighs 500N and stands on one end of a seesaw. She is 0.5m from the pivot.

What moment does she exert?

moment = 500 x 0.5

= 250 Nm

moment equation
Moment equation

moment = force (N) x distance from pivot (cm or m)

moment

f

x

d

The moment of a force is given by the equation:

Moments are measured in Newton centimetres (Ncm) or Newton metres (Nm).

principle of moments
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 moments15
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
Principle of moments – calculation

Two girls are sitting on opposite sides of on a see-saw. One girl weighs 200N and is 1.5m from the pivot. Where must her 150N friend sit if the seesaw is to balance?

When the see-saw is balanced:

total clockwise moment = total anticlockwise moment

200N x 1.5m = 150N x distance

200 x 1.5 = distance

150

distance of second girl = 2m

why don t cranes fall over

trolley

load arm

counterweight

loading platform

tower

Why don’t cranes fall over?

Tower cranes are essential at any major construction site.

Concrete counterweights are fitted to the crane’s short arm. Why are these needed for lifting heavy loads?

why don t cranes fall over19

3m

6m

10,000N

Why don’t cranes fall over?

Using the principle of moments, when is the crane balanced?

?

moment of = moment of

load counterweight

If a 10,000N 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 over20

counterweight x

moment of

counterweight

distance of counterweight from tower

=

= 10,000 x 3

= 30,000 Nm

moment of

load

load x distance of load from tower

=

= ? x 6

moment of load = moment of counterweight

? x 6 = 30,000

? = 3,000

6

?= 5,000 N

Why don’t cranes fall over?
crane operator activity
Crane operator activity

Where should the loading platform be on the loading arm to carry each load safely?