1 a What Are Points X and Y Called?

HELP

Look at these pictures of some everyday objects.

1 a What are points X and Y called?

b George needs to change the wheel on his lorry. He tries to undo the wheel nuts using spanner A. He cannot move the nuts.

i Why can't George move the wheel nuts?

ii Which other object might solve the problem?

iii Why might this object work better?

iv He still cannot undo the nuts. He has a long piece of pipe handy. What else could he do?

v Now he is successful. Explain why.

CORE

2 The diagram shows the brake on a bike handlebar. The brake lever is attached to a cable that pulls the brakes onto the wheel.

a Where is the pivot of the lever?

b Where should the cyclist apply her force to give the easiest braking action?

c i How would the force on the brakes be changed if the brake lever was shortened?

ii What must the cyclist do to keep the same force on the brakes, even though the lever is shorter?

3 Bob the plumber wants to turn off the water at the stop-tap outside a house. He uses a special tool to do this.

a Which letter shows the position of the pivot?

b Bob pulls on the tool at point X but the tap does not move.

i Describe two ways in which Bob can increase the turning force on the tool.

ii The tap still does not move. Bob hits the tool hard with a large hammer at point Y. Now the tap moves. Explain why the tap moves now.

EXTENSION

4 Look at the scissors on the right.

a Where is the pivot on the scissors?

b How would you redesign the scissors to increase the force on the cutting blades?

c i Where, on the cutting blades, will the cutting force be greatest? (Hint: on a seesaw, a heavy person can sit closer to the pivot than a lighter weight person.)

ii Explain why this point has the greatest force.

5 Dimitri is a gymnast. He trains by doing pull-ups on a high bar. His friend Janni also does pull-ups. Dimitri's arms are longer than Janni's. They both weigh the same and their arm muscles exert exactly the same force. The diagram shows how he does this.

a Where, in the gymnast's arm, is the pivot?

b i Which of the gymnasts will find it harder to do each pull-up?

ii Explain why this gymnast will find it harder.

© Harcourt Education Ltd 2004 Catalyst 3

This worksheet may have been altered from the original on the CD-ROM.