A Pulley is a simple machine. It is usually used to lift things by pulling down a rope that passes over the pulley. In a single pulley
the amount of effort or force needed to rise the load is equal to the
weight of the load. In a multiple pulley system there are two or more pulleys and the effort needed to rise the load is much less than the weight of the load.
How
to make a pulley?
Method
1 - Pulley made from corrugated cardboard
Step
1: Cut
2 bigger circles and a slightly smaller circle from a corrugated
cardboard. Make a hole in the center of every cardboard circle.
Step
2 : Sandwich
the smaller circle in-between the two larger cardboard circles with glue. Pass a pencil (any axle) through the
hole so that the pulley wheel rotates freely. Your pulley is ready!
Step 1
Step 2
Method
2 : Smooth and Stronger pulley
Things
Needed : Craft paper, glue, pencil, packaging box
Step
1 : Cut
thin and long strips of paper about 4mm width. Roll as many strips of
paper on to a pencil depending on the size of the pulley you want to
make.
Step
2 : Cut
2 circles from a packaging box, make holes in the center and
sandwich the paper roll between the 2 circles. Your pulley is ready.
Step 1
Step 2
Single
Pulley Experiment - A Well
Things
Needed : A
pulley, rope, a toy bucket, a plastic container, 3 pencils,
sticky tape, paper.
Step
1 : Draw
and paint bricks on the sheet of paper and stick it around the
plastic container such that it looks like a well.
Step
2 : Stick
two pencils to the inner side of the container so that 70% of the
pencil protrudes above the container. Then insert the pulley into the
third pencil and then bind the third pencil horizontally to the two pencils
with a thread or sticky tape.
Step
3 : Fill
half of the container with water. Tie a bucket to a rope and then
sling the rope on to the pulley. Fill the bucket with water and pull
it out with the help of a pulley wheel. Have
a nice time drawing water from the well ! Observe that lifting a bucket of water using a pulley is easier than lifting it directly from the well.
Multiple Pulleys
A
multiple pulley system consists of two or more pulleys. There are 2
blocks of pulleys namely the upper block and the lower block
(tackle). The upper block pulleys are fixed where as the lower
block pulleys are attached to the load and moves along with the load. A
rope is wound around both the sets of pulley wheels. As the number of
pulleys increases a smaller effort is sufficient to pull a heavy load; but the load need to be pulled over a longer distance. The figure
shows 1,2,3,4 and 6 pulley system respectively.
Experiments
for multiple pulleys
A
simple 2 pulley experiment to test whether the effort required to
lift a load of 30 units is half its weight (i.e 15 units). Repeat the experiment with 3-pulleys, 4-pulleys and
so on. When 3-pulleys are used the effort should be 1/3 rd and when
4-pulleys are used it should be 1/ 4 th the load.
Elevator
Experiment
The
Elevator technology uses two or more pulleys for lifting the Elevator.
Heavy elevators can be easily lifted using a smaller counter weights
and motors. A working model of an elevator can be built using cardboard boxes, LEGO blocks or other building materials. The upper block pulley should be fixed at the top and the lower block pulley should be attached to the elevator so that it moves along with the elevator. Tie a rope to a beam from the upper block and wind the rope over the lower and upper pulleys. Pull the free end of the rope to lift the elevator. Building and
executing the elevator technology is left to the creativity of the
child.
We
have used LEGO blocks for the construction of elevator and its
support. For the pulleys we have used the wheels by removing the
outer rubber of the wheels. We are manually pulling the
rope to lift the elevator. Instead you could use a smaller counter
weight (½ the weight of the elevator in a 2 pulley system) or a
motor to wind the rope on to a bobbin.
Video
of the working model of our elevator
