A What Do Scientists Call the Balance Point in Tim's Body?

HELP

1 Tim is learning to balance for his family's circus act. He is balancing on his left leg with his arms stretched out on each side. His body is leaning over to the left.

Tanya throws him a heavy juggling club. Tim catches it in his left hand. He overbalances and falls over.

a What do scientists call the balance point in Tim's body?

b i Which way must Tim stretch his right leg to stay in balance?

ii What would happen if he did not do this with his right leg?

c When Tim catches the club his balance changes.

i What sort of effect does the weight of the club produce?

ii Which way does he fall?

iii Why does he fall in this direction?

iv What could he do to stop himself from falling over?

CORE

2 The diagram shows a security barrier outside a police station car park. The beam is exactly balanced and is not resting on the right-hand support pole.

a What is point R called?

b Why is point R very important for calculating moments?

c i What is object P usually called?

ii What is the purpose of object P?

d i Object P is suspended from the barrier 0.5 m to the left of point R. Calculate the anticlockwise moment produced by the force.

ii The beam to the right of point R is 5 m long. Calculate the downward force of the beam at its right-hand end.

e i What would you do to object P if the beam was made a metre longer on the right?

ii Explain why this would help.

EXTENSION

3 The diagram shows an old industrial lever used to stamp out pieces of metal from a metal sheet. The operator pushes down on the right-hand end of the handle. The machine is shown at rest. The downward force of 50 N is just the weight of the handle.

a Calculate the moment, in Nm, of the 50 N weight about the pivot.

b When the machine is at rest, what is the downward force exerted by the punch?

c To punch out a piece of metal requires a total downward force of 1000 N on the punch. What is the additional force that the operator must use to push down on the handle?

d The operator now needs to stamp a mark onto the punched out piece of metal. He changes the punch for a patterned stamp. The stamp has a surface area of 5 cm2. He pushes down on the handle with the same force as before.

i Calculate the pressure that this force exerts on the punched out disc.

ii Explain why the stamp only makes an impression on the metal but the punch cuts right through it.

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