Pulleys
Pulleys A pulley is a simple machine that uses grooved wheels and a rope to raise, lower or move a load.
Draw the diagram and label the arrow. FORCE = N Using your spring scale, lift the object up straight up. Record the amount of force needed. load
Fixed pulley Draw this diagram in your notes. Label the arrows. load
Spring scale attaches here Now, using one pulley, attach the object to one end of the string. On the other, attach the spring scale. Gently pull, using a constant motion to lift the object. Record the force needed.
Did the amount of force needed to lift the load change? Fixed pulley NO! Amount of force stays the same, but the direction of the force changes with a fixed pulley. load
Draw this diagram and label the arrows. movable pulley load
What was the force needed to lift the load with one movable pulley? A moveable pulley decreases the amount of force needed to lift the load. The cupboard is taking part of the load, so less force is needed.
fixed pulley load movable pulley Draw the diagram and label the arrows.
Attach spring scale Now we will use 2 pulleys. Tie one end of the string to a handle on the cupboard. Thread in the string on the pulley that attaches to the weight. Then thread the string into the pulley already attached to the handle. Finally, attach the spring scale to the free end. Again, pull in a constant motion. Record the force needed to lift the weight.
What was the amount of force need to lift the load with a fixed and movable pulley? The more pulleys, the less force needed to lift a load.
The only thing that changes is the direction of the force you have to apply to lift the weight. You still have to apply 100 pounds of force to lift the weight.
With the pulley tied to the cupboard, ½ the force is carried by the cupboard.
By using two 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.