79 Simple and Complex Machines-High

Simple and Complex Machines Written by Ned Jensen

Introduction How do you do work? How do you eat cereal or hit a baseball really far? How do you slice cheese for a sandwich or loosen the lid of a jar? You probably use tools. People have been making and using tools for millions of years. We create tools to 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. Hammers and knives are simple machines. Some machines combine several simple machines. Clocks and bicycles are complex machines. In this book, you will learn about machines and how they make work easier.

Do You Know? Animals use tools, too! Apes use sticks to get ants out of anthills. Otters use rocks to crack open clamshells. Crows can make wire hooks to get food out of a tall, thin container. In the introduction, you learned that machines make work easier. But what do we mean by work? In science, work is done whenever an object is moved over a distance. To move something, you must use force. The more force it takes to move an object, the more work is done. The greater the distance the object moves, the greater the amount of work it takes to move it. Whenever you push, pull, turn, or lift an object, you are using force to move it. The amount of force it takes depends on the weight of the object. It takes a lot more force to move a large boulder than to move a small rock. Machines make work easier by reducing the amount of force, or effort, it takes to move an object, or load.

But there is a trade-off when you use a machine to reduce the force it takes to do work. The trade-off is that you have to apply the force over a greater distance. Most machines help you do work by spreading out the force over a larger distance.

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

Inclined Plane The inclined plane is a very simple machine. It has no moving parts! It is a surface with a slope, or incline. Inclined planes are used to change the height of an object. A common inclined plane is a ramp. Furniture movers use ramps because it takes less force to slide a heavy box up an inclined plane than to lift it straight up into a truck. It would take a certain amount of force to lift a box three meters. But if you use a ramp that is six meters long to raise the box three meters high, it takes only half the force! The longer the ramp and the gentler the slope, the less force is needed to move the load. But remember the trade-off. The gentler and longer the slope, the farther you have to push or pull the load.