Activity

Pulley free play

Summary
Students are given pulleys, string and cups of counters to experiment freely with. They can also use water and other things to lift and be lifted.
Science content
Physics: Motion and Forces, Newton’s Laws, Gravity (K, 2, 6)
Physics: Simple and complex Machines (5)
Materials
    Pulley kit in a baggie for each pair or group of three:
  • bar to bridge desks and hang pulleys from
  • masking tape to secure bar
  • 2 large binder clips
  • two or more single pulleys
  • 1m and 2.5m strings (use braided cord, the ends dipped in 1:1 white glue:water)
  • 2 small cups with handles (make from masking tape if needed)
  • 2 mini binder clips
  • 20 or 30 counters e.g. glass or something similarly small yet heavy
  • optional: other materials to lift and use as weights, including water if desired
Procedure

Show students how to set up their bar, spanning it between two desks, or chairs, and taping to stop it moving around.
Using a large binder clip, hang the pulley from the bar. Or they can attach their pulleys elsewhere in the classroom using the large binder clip. Show them how to thread the string through a pulley and add a cup to each end of it using the small binder clip, then add counters.

Ask them to experiment freely with the pulleys. Give them ideas if they need them, writing them on the board to get them started, and adding as students find new ways to use them.
The youngest students I would help them set up one string over one pulley, then ask them to move the cups up and down with counters. They can be challenged to raise a flag, given some paper to tape or clip to one of the strings.
Older students can be challenged to raise a cup of counters both fast and slowly, balance two cups either side of a pulley, drag an object over their desk using counters in a cup and a pulley, or make a zipline. A clever system can be set up by hanging weights below a pulley which sits on top of a line.

Discussion with what they discovered should include how pulleys change the direction of a force. Counters in a cup or pulling down on a string in one direction moves an object in the opposite, or another, direction.
Show images of simple fixed pulleys that change the direction of a force on a flagpole.

Discussion around how objects can be balanced in two cups either side of a pulley, or one cup can be moved up slowly, can lead to how an elevator works. An elevator is a heavy car which the people go it, with a counterbalance on the other side of the pulleys. As both these items are heavy, and nearly balanced on each side of a pulley, it does not take much force from the motor to move the car up and down (while the counterbalance moves in the opposite direction).

Students may notice, or can be asked to compare how many counters are needed to lift an object when the string goes through the pulley, or simply loops over the bar. This demonstrates how pulleys reduce friction by turning when the string moves over them. Without a pulley, it takes more forces to pull the string.

Grades taught
Gr K
Gr 1
Gr 2
Gr 3
Gr 4
Gr 5
Gr 6
Gr 7
Teaching site
Tyee Elementary
Xpey' Elementary School (formerly MacDonald Elementary)