Pulley
Nathan, Blanca
What it is
a pulley is a wheel with a grooved rim around which a cord passes. It acts to change the direction of a force applied to the cord and is chiefly used (typically in combination) to raise heavy weights.
How it provides mechanical advantage
It changes the direction of the force. This can be an advantage in cases where you would have to pull something upwards, using only your muscles, because by changing the direction you can use your weight too. You do the same amount of work, but less force has to be applied over a greater distance.
Examples
Elevator
in an elevator, cables are attached to the car and are run through a pulley at the top of the shaft. The other end of the cables are attached to a heavy steel weight called counterweight. When the car goes up, the counterweight goes down and viseversa
Lifting a flag
on top of a flag pole there is a pulley that works by lifting the flag up when you pull down on the other side of the rope
Practice problem
Mechanical advantage = Out Put Force / In Put Force
1) Laura wants to lift up the 150N mainsail of a sailing boat. To do this, she uses a pulley to connect one end of the rope connecting with the mainsail to the other end of the rope and pulls down on it to lift the mainsail. If Laura weights 250N, what is the mechanical advantage of using a pulley to lift up the mainsail?
Answer
mechanical advantage= 250/150 = 1.67N