Manual Knex 78610 - Education Intro to Levers and Pulleys Teachers Guide (page 47 of 62) (English)

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Lesson�7:�The�Flagpole

• Howmightthechildrenmeasuretheforcesneeded?

Teacher’s Notes

A force meter could also be used for

these activities to enable the children

to take direct measurements. If you

have not already done so, demonstrate

how a force meter is used to measure

forces and explain that the unit of mea-

surement is Newtons (N).

Step 3: Ask the children to repeat Step 2 but only this

time they should measure the distances moved by their

hand (the effort) when pulling on the string and the

distance moved by the mass (the load). One child should

grip the string just below the pulley and pull down slowly

to lift the load. Another child then measures:

(i) how far the string has been pulled

(ii) how far the load has been raised above the desktop.

 • Whatdotheirmeasurementstellthemabouthowa

fixed pulley works?

To lift a load the children would have to

pull on the rope with at least as much

force as the weight of the load. They

might test this by connecting a force

meter to either end of the pulley rope,

pulling each force meter and recording

the reading.

The distance moved by the effort and

the load is the same. If force meters

have been used then, in theory, the

values obtained for the effort force and

load should also be the same. In reality,

however, the effort force is likely to be

larger because of the additional effect

of friction in the pulley system. Fixed

pulleys only change the direction of

movement or the applied force; they

do not amplify the force.

 • Askeachgrouptorecordandexplaintheirfindingsand

observations by writing and making labelled drawings.

They should indicate the direction of the applied forces,

the direction of movement of the pulling force and the

object being raised. The children should be encouraged

to use the correct scientific vocabulary.

To promote the wider use and

application of ICT skills and practices,

the children’s models and work might

be recorded using a digital camera.

Teacher’s Notes

When the load is pulled upwards,

the pulling force is greater than the

weight of the object – the forces are

unbalanced. When the object is held

still, the forces are balanced – it is

not moving. The force applied on the

rope end equals that of the weight on

the other end. When released it falls

because there is now no upward pull-

ing force but only the force of

gravity pulling it downwards.

Optional Activity for Step 3

 • Askthechildrentodescribewhattheyhaveobserved

in terms of balanced and unbalanced forces.

Education

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Knex 78610 - Education Intro to Levers and Pulleys Teachers Guide Manual

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