Pulleys

Assignment #35

A PULLEY is a simple machine that uses grooved wheels and a rope to raise, lower or move a load.

There are 2 types of pulleys: fixed and movable.

FIXED MOVABLE

1. Draw the diagram and label the arrows as indicated.2. Using your spring scale, lift the object straight up.3. Record the amount of force needed to lift the object in your journal.

load

FORCE = ___________ N4

Draw & label this diagram in your journal.

Fixed Pulley

load

fixed pulley

Attach the load to one end of the string. Then, thread the string through the fixed pulley. On the other end, attach the spring scale. Gently pull, using a constant motion to lift the object. Record the force needed in journal.

Springscale

attacheshere!

FORCE = ___________ N

fixed pulley

load

4

Did the amount of force needed to lift the load change?

NO!

The amount of force needed to lift the object stays the same, but the direction of the force changes with a FIXED pulley.

fixed pulley

load

Movable Pulley

Draw & label this diagram in your journal.

movable pulley

load

Movable Pulley

movable pulley

load

Attach the string to the paperclip on the cabinet door handle. Run the string through the movable pulley as shown. Attach load to movable pulley (use the hook). Attach the spring scale to the other end of string. Gently pull up, using a constant motion to lift the object. Record the force needed in journal.

Spring scale attaches here!

What was the force needed to lift the load with one movable pulley?

A MOVABLE pulleydecreases the amount of force needed to liftthe load.

Note: The cupboard is taking part of the load, so less force is needed.

FORCE = ________ N3

Draw the diagram and label the arrows.

load

fixed pulley

movable pulley

Now we will use 2 pulleys. Paperclip one end of the string to a handle on the cupboard. Thread in the string through the movable pulley that attaches to the load. Attach load to this pulley. Then, thread the string through the fixed pulley attached to the handle. Finally, attach the spring scale to the free end. Pull down in a constant motion. Record the force needed to lift the load.

Spring scale

attaches here!

movable pulley

fixed pulley

Attach string to paperclip

here!

The more pulleys, the less force needed to lift a load.

What was the force needed to lift the load with a fixed AND movable pulley?

FORCE = ________ N2

The only thing that changes is the direction of the force you have to apply to lift the 100# load. You still have to apply 100 pounds of force to lift the load.

Fixed Pulley

With the pulley tied to the cupboard and using a movable pulley, ½ the force is carried by the cupboard.

Movable Pulley

By using 2 pulleys, the weight is split equally between the two pulleys, so each one holds only half the weight. You only have to apply 50 pounds of force because the ceiling exerts the other 50 pounds of force.