Year 7 & 8 TOC

Levers & Pulleys

Simple machines

LO: Investigating a simple machine such as a lever or a pulley system

Simple machines, are exactly as the name suggests. Levers, Pulleys, wedges, ramps, wheels and axles are examples of simple machines. They typically only need single force to work correctly.

Simple machines are designed to decrease the amount of effort required to move an object. Using these machines, we have a mechanical advantage.

Did you know? Static shock

Have you ever had a static shock? When you drag your feet on the ground you build up a positive charge and when you go close to someone the charge jumps to the other object.

Mechanical advantage

Mechanical advantage allows us to move large or heavier objects with less force. Mechanical advantage can be calculated by dividing the size of the load by the the size of the effort.

We can use simple machines as force magnifiers or distance magnifiers. Force magnifiers change a weak force into a strong force. For example, if we use a crowbar, we don’t have to put much force behind it to move heavy objects. Distance magnifiers can turn a strong force over a short distance, to a weak force over a long distance.

Levers

Levers are an extremely useful simple machine. They’ve been used all throughout history to help create some of the most amazing structures in the ancient world. In fact we use the same principles our ancestors used in basic tools today. Scissors, pliers, shovels, wheelbarrows and seesaws are all examples of levers.

Components of levers

We can break up a lever into 3 sections:

The further away the effort is from the fulcrum, the more load you can lift. For example, 1 person can lift 2 people on a seesaw, if the single person is 2 meters from the fulcrum.

Types of levers

We can break levers up into 3 classes. The only difference between these classes is the position of the load, fulcrum and effort

First-class lever

The fulcrum is placed in between the load and effort.

Effort – Fulcrum – Load

It is the most typical lever configuration. You’ll see this in Seesaws, Scissors, Pliers and Catapults. What you notice is, as the effort moves one direction, the load will move in the opposite direction. In a seesaw you push down (effort) and the load goes up.

Second-class lever

The Load and Effort are both on the same side of the fulcrum. The effort is further out than the load.

Effort – Load – Fulcrum

You’ll see these types of levers in Wheelbarrow, crowbar and nut crackers. Unlike class 1, the effort and load are both moved in the same direction.

Third-class lever

I this case, the Effort is in between the load and fulcrum.

Load – Effort – Fulcrum

Tweezers, staplers and mousetraps are examples on class 3 levers.