78 Simple and Complex Machines-Mid

Simple and Complex Machines Written by Ned Jensen

Introduction How do you do work? How do you eat cereal or loosen the lid of a jar? You probably use tools. Tools make work easier to do. A machine is a device that uses energy to help us do work. Tools that have only a few parts are called simple machines. A hammer is a simple machine. Some machines combine several simple machines. Clocks and bicycles are complex machines. In this book, you will learn how machines make work easier.

Do You Know? Animals use tools, too! Apes use sticks to get ants out of anthills. Sea otters use rocks to crack open clamshells. Crows can make wire hooks to get food out of a tall, thin container. What do we mean by work? In science, work means moving something. To move something you use force. The more force it takes to move an object, the more work is done. The more distance something moves, the more work is done. Whenever you push, pull, turn, or lift an object, you use force. The amount of force it takes depends on how heavy the object is. It takes a lot more force to move a big rock than to move a small rock.

Machines make work easier by reducing the amount of force it takes to move an object, or load. But there is a trade-off. Machines make your work easier, but you have to work over a longer distance.

Types of Simple Machines There are only a few types of simple machines. Some have no moving parts. Some have just a few moving parts Below are the seven simple machines you will read about in this book.

Inclined Plane The inclined plane is a very simple machine. It is a surface with a slope, or incline. Inclined planes help us change the height of heavy objects. A common inclined plane is a ramp. Furniture movers use ramps. It is easier to slide a heavy box up a ramp than it is to lift the box straight up. Moving the box up the slope of a ramp takes less force. The longer the ramp is and the gentler its slope, the less force it takes to move a box up it. But remember the trade-off. The gentler and longer the slope, the farther you have to push or pull the load.