Title: Pulleys, Forces and Distances

Introduction:

Pulleys have been around for hundreds of years. The ancient Greeks even had pulleys. Pulleys have been around so long that nobody knows when they were invented.

Pulleys are used for:

• Ships for lifting cargo and sails
• Lifting heavy things
• Changing the direction of the pull
• Lifting logs and other heavy stuff
• On cranes for lifting heavy building materials

Question:

Why are pulleys useful?

Hypothesis:

I think that pulleys will make a big difference when I lift something.

Experiment:

Part A: Simple Pulley Force

Part B: Simple Pulley Distance

Part C: Double Pulley Force

Part D: Double Pulley Distance

Equipment Used:

• two 1000 gram spring scales
• one single pulley
• one double pulley
• 10 feet of nylon rope
• a test fixture frame

Results:

Part A: Forces when using a simple pulley.

W1	W2	W2÷W1
100 g	200 g	2.0
200 g	400 g	2.0
300 g	600 g	2.0
400 g	800 g	2.0

We also put a scale to measure the other force (W3) pulling down.

W1	W3	W3+W1	W2
100 g	100 g	200 g	200 g
200 g	200 g	400 g	400 g
300 g	300 g	600 g	600 g
400 g	400 g	800 g	800 g
400 g	400 g	800 g	800 g

This means that the two forces pulling down together (W1 and W3) equals the force pulling up (W2) or W1 + W3 = W2. And W1 and W3 are equal, so 2 times the force pulling down equals the force pulling up!

Part A Data Sheet

Part B: Distances when using a simple pulley.

D1	D2	D1÷D2
0 cm	0 cm	0.0
10 cm	9.5 cm	1.1
20 cm	9.5 cm	1.1
30 cm	9.5 cm	1.1

Part B Data Sheet

Part C: Forces when using a double pulley.

W1	W2	W2÷W1
100 g	200 g	2.0
200 g	400 g	2.0
300 g	700 g	2.3
400 g	900 g	2.3

Part C Data Sheet

Part D: Distances when using a double pulley.

D1	D2	D1÷D2
0 cm	0 cm	0.0
10 cm	3.2 cm	3.1
20 cm	3.2 cm	3.1
30 cm	3.4 cm	2.9

Part D Data Sheet

What I Learned (Conclusion):

I learned that pulleys can lift heavier things that we can’t. You can also use pulleys to change the direction of the pull. In Part C we can pick twice as much weight. But we have to pull three times as much rope.

References

http://nerds.unl.edu/pages/preser/sec/skills/Pulley/_private/introduction.htm

http://en.wikipedia.org/wiki/Pulley