Physics for Kids: Simple Machines in Automobiles

Imagine you've been asked to move a heavy boulder across your backyard. When we need to exert a force across a certain distance in order to move an object, it is called work. Simple machines are basic tools that make that work easier for us. They are simple because they have few moving parts or none at all. Simple machines don't change the amount of work being done, but they can make the work seem easier by changing the size and direction of the force or the distance. The six simple machines are the lever, the inclined plane, the wedge, the wheel and axle, the pulley, and the screw. A compound machine is any combination of two or more simple machines. Imagine you had a wheelbarrow to help you move the heavy boulder. A wheelbarrow is a compound machine because it is a combination of two simple machines, the lever and the wheel and axle. Most of the machines you encounter in everyday life, from the clock on your wall to the lawn mower in your shed, are compound machines made of simple machines. Even the car parts in your neighbor's new automobile are made of simple machines.


A lever is a simple machine that consists of a long rod or board that rests on a fixed turning point called a fulcrum. This tool can be used to lift a heavy object or load. The lever makes this work seem easier by decreasing the force necessary to lift the object while increasing the distance covered by that force. When the fulcrum is closer to the load, it will be easier to lift. Some common examples of levers are see-saws and crow bars. The turn signal in an auto is also a kind of lever.

Inclined Plane

An inclined plane is simply a flat surface that is higher on one end than it is on the other. An inclined plane can be used to move a large and heavy object to a higher position. Moving an object up an inclined plane is easier than lifting it because the inclined plane changes the size and direction of the force as well as the distance. When you use an inclined plane, a smaller force is necessary to move the object. Some common examples of inclined planes are ramps and slides.


When you combine two inclined planes, you get a wedge. Wedges can also be round. They are simple machines that are wider on one end and thinner on the other. Wedges can be used to separate things, as in the case of axes, but they can also be used to hold things together, as in the case of push pins. Some common examples of wedges are nails, chisels, shims, and doorstops.

Wheel and Axle

A wheel and axle is a tool that consists of a circular object called a wheel with a rod called an axle going through its center. When the wheel and axle turn together, the wheel travels a greater distance with a weaker force and the axle travels a smaller difference with a greater force. When a force is applied to the axle, this simple machine can be used to increase speed because the wheel travels a greater distance in a shorter amount of time than the axle would be able to on its own. When a force is applied to the wheel, the tool can be used to multiply force because the axle will turn a smaller distance with a greater force. Common examples of wheel and axle machines include doorknobs and windmills. An automobile contains many examples of this simple machine; wheels and axles can be found in car parts like steering wheels and tires.


A pulley is a simple machine that is sort of like a wheel and axle combined with a rope or a cord. The cord is wrapped around the wheel or axle and can be pulled on one end to lift an object on the other end. The wheel changes the direction of the force so that when you pull down on the rope, the object goes up. Two or more pulleys can be combined to create a pulley system like a block and tackle. Examples of pulleys and pulley systems might include a crane or the accessory belt in an auto. Pulleys are also used in elevators to move the car up and down between floors.


A screw is basically an inclined plane that has been wrapped around a cylinder. A screw can be used to move an object to a higher position, but it takes up less horizontal space than a regular inclined plane of the same length. Screws can also be used to keep things together. Common examples of screws include metal screws used in construction, jar lids, and spiral staircases.

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