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## PowerPoint Slideshow about ' Lesson Thoughts' - yoshio-beasley

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Next: Run through the demos, then get S to design own pulley, work out it’s MA, then build it.

This might require much more than one lesson!!

Need worksheets – basically pages 4-6 plus a blank table for S design (a missing slide 7).

I could – run through the demos, then hand out the worksheets, for S to work through themselves. This should give them more time to work on their own pulley system.

Actually if I have a separate sheet, do I need everything on the slide??

Yes - because S will see on the whiteboard what they see on their paper, and I can write on the white board.

No - because it is on the sheet, and it clutters up the slide

Story - stairs up to my relocated house.

Combining more than one pulley means that big weights can be lifted with very little effort.

BUT for each metre raised, much more rope has to be pulled through.

Mechanical Advantage

Count the number of rope sections.

If the rope is pulled up , the number of rope sections = the MA (Mechanical Advantage).

If the rope is pulled down , then minus 1 from the number of rope sections. This number then = MA (Mechanical Advantage).

Divide the weight to be lifted by the mechanical advantage to find out how much force is required to lift.

Watch the demonstration.

Work out the MA (Mechanical Advantage)

Number of strings = N

If Pull up , p = 0

If Pull down , p = 1

MA = N - p

Note: Effort = Mass/MA

Take spring balance

measurements as follows:

Effort

Mass MA Mass Balance

/MA

100 1 100 ?

300 1 300

500 1 500

What do you notice?

Mass

Pulleys 2: Movable

Watch the demonstration.

Work out the MA (Mechanical Advantage)

Number of strings = N

If Pull up , p = 0

If Pull down , p = 1

MA = N - p

Note: Effort = Mass/MA

Take spring balance

measurements as follows:

Effort

Mass MA Mass Balance

/MA

100 2 50 ?

300

500

What do you notice?

Pulleys 3: Combined

Watch the demonstration.

Work out the MA (Mechanical Advantage)

Number of strings = N

If Pull up , p = 0

If Pull down , p = 1

MA = N - p

Note: Effort = Mass/MA

Take spring balance

measurements as follows:

Effort

Mass MA Mass Balance

/MA

100 ? ? ?

300

500

What do you notice?

Pulleys 4: Your Choice

Equipment: pulleys (single or double), string, 1 spring balance

Design a pulley system using

more than two pulleys:

Work out the MA and

how much effort you will need.

Build your pulley system.

Take spring balance

measurements as follows:

Effort

Mass MA Mass Balance

/MA

100 ? ? ?

300

500

What do you notice?

How many pulleys?

Pull Up ?

? ?

Pull Down ?

How many pulleys?

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