Levers and Pulleys
Can you lift a young elephant on your own? Slide the fulcrum, pick a lever or add pulleys, and find out how simple machines turn a small push into a big lift.
ICSE Class 10 MachinesTry this
0 of 5 doneBalance the seesaw exactly, so neither side goes down.Hint: Class 1. Slide the fulcrum or change your push until it says Balanced
Lift the 500 kg cow with a lever, pushing less than 1000 N.Hint: put the fulcrum (or the load) very close to the cow
Use a Class 3 lever to lift a load. Notice anything odd about the effort?Hint: the effort sits between the fulcrum and the load
Lift the 150 kg motorbike with pulleys, pulling less than 400 N.Hint: more ropes holding the load means less pull
Pull 3 m of rope and lift the load just 50 cm.Hint: count the ropes. 3 m ÷ ropes = height
What's happening
Levers trade distance for force
A lever turns around a fixed point, the fulcrum. The turning effect of a force is force × its distance from the fulcrum. Push far from the fulcrum and a small force can balance a big load close to it, but your end has to move much farther.
Three classes of lever
Class 1 has the fulcrum in the middle (seesaw, scissors). Class 2 has the load in the middle (wheelbarrow, nutcracker): it always makes lifting easier. Class 3 has the effort in the middle (tweezers, your forearm): it needs more effort than the load but moves the load faster and farther.
Pulleys share the load between ropes
A single fixed pulley only changes the direction of your pull. Add movable pulleys and several rope sections hold the load together, each carrying an equal share. You pull with less force, but have to pull that many times more rope. The work you do stays the same.
Who figured this out?
Shadoof
About 2000 BCE, Egypt and MesopotamiaOne of the oldest machines: a long pole on a pivot with a bucket on one end and a heavy counterweight on the other, used to lift river water for farms.
Archimedes
About 250 BCE, SyracuseWorked out the law of the lever and is said to have boasted: “Give me a place to stand, and I will move the Earth.”
Hero of Alexandria
1st century CE, EgyptDescribed the simple machines, including the lever, the pulley and the wheel and axle, and how they let a small force move a heavy load.
Learn more
- Lever · Wikipedia
- Pulley · Wikipedia
- Mechanical advantage · Wikipedia
Check yourself
1. In a seesaw, where should a lighter child sit to balance a heavier one?
2. Which is a Class 2 lever?
3. A block and tackle has 4 rope sections holding a 400 N load. What effort is needed (ideal)?
4. Does a machine reduce the work you do?
Common questions
What are the three classes of levers?
In a Class 1 lever the fulcrum is between the load and the effort (seesaw, scissors, crowbar). In a Class 2 lever the load is between the fulcrum and the effort (wheelbarrow, nutcracker, bottle opener). In a Class 3 lever the effort is between the fulcrum and the load (tweezers, fishing rod, the human forearm).
What is mechanical advantage?
Mechanical advantage (MA) is how many times a machine multiplies your force: MA = load ÷ effort. For a lever it equals effort arm ÷ load arm. MA greater than 1 means the machine makes lifting easier.
What is velocity ratio?
Velocity ratio (VR) is the distance moved by the effort divided by the distance moved by the load in the same time. For an ideal machine MA = VR. Efficiency = MA ÷ VR, which is always less than 100% in real machines because of friction.
What is the mechanical advantage of a single fixed pulley?
The mechanical advantage of a single fixed pulley is 1: the effort equals the load. It is still useful because it changes the direction of the force, so you can pull down to lift something up, as with a well or a flagpole.
How do you find the mechanical advantage of a block and tackle?
For an ideal block and tackle, the mechanical advantage equals the number of rope sections supporting the movable block. With 4 supporting ropes, a 400 N load needs only 100 N of effort, but the effort must move 4 times as far.
Why is a Class 3 lever useful if it needs more effort?
A Class 3 lever has MA less than 1, but a small movement of the effort makes the load move a long way quickly. That's why your forearm, a fishing rod and a broom are Class 3 levers: they give speed and reach rather than strength.
Ideal machines: no friction and weightless planks, pulleys and ropes. Real machines need a little more effort.
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