Q1: COMPARING WEIGHTS ON A PULLEY:

Video: Simple machines - Pulleys

• IF UNABLE TO ACCESS YOUTUBE VIDEO (requires Flash) TRY:Simple machine - Pulleys

Video: Simple machines - The Wheel & Axle

• IF UNABLE TO ACCESS YOUTUBE VIDEO (requires Flash) TRY:Simple machines - The Wheel & Axle

Click on weights and blocks to set up experiments - you can also left-click and drag items on left-hand side of simulator.

Click and drag items to create experiments and to find out how it works - menu bar is at bottom of the simulator screen. More about levers.

Reminder:

• A force is a push or a pull.
• Forces do not cause motion; forces cause acceleration.
• Identify what forces are affecting the weights.
• Identify the locations where forces are acting & what direction they are acting in.

AN EXAMPLE EXPERIMENT: This is an experiment to help you understand the difference between a simple lever (like a 'see-saw', 'teeter-totter' or balance bar) and a simple pulley (like a hook that has no friction).

An example observation might be:

• Equal weights placed at equal distances on a horizontal balance bar (see-saw) remain in balance.

An example hypothesis might be:

• When two weights are placed the same distance from a fulcrum the weights/balance will not move.
• When one weight is moved closer to the the fulcrum, one end of the balance will fall.
• I expect the result will be the same when the position of the weights is changed, both for the pulley and for the balance.

An example experiment to test my hypothesis (using alternative strategies and the resources provided in the student wiki):

1. Set up the balance and pulley as shown in Fig 1.
2. Place the two EQUAL weights at EQUAL distance from the fulcrum (mark 6)
3. Shorten the length of one arm by moving one weight closer to the fulcrum (eg. mark 4)
4. Describe what happens to the weights. Does one weight go up, go down or stay the same?

Fig 1. Weights set at equal distances on the balance (see-saw) and on the pulley

NEXT, consider this:

1. Set up the balance and pulley as shown in Fig 2.
2. First, position the two EQUAL weights at EQUAL distance from the pulley
3. Now shorten the length of one arm (rope) by moving one weight closer to the pulley
4. Describe what happens to the weights. Does one weight go up, go down or stay the same?

Fig 2. Weights set at unequal distances on the balance (see-saw) and on the pulley

• Q: Are the results of both of these experiments the same?
• A: Place your answer below - in the box titled 'Post your comments here:'

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