34 Machines That Build

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Machines That Build by Whit Fisher

Chapter 1 What Is Work? Do you know what work is? The word work means different things to different people. For some people, work means a job they go to every day. Others say that thinking is hard work. An athlete might say that exercising is work. What do you think work is? Scientists have their own meaning of work. They say work is done when a force changes the motion of an object. Pushing a box across the floor is work because a force is moving the box. When you push or pull an object and change its motion, you are doing work. What about pushing against a wall? If the wall does not move, no work has been done.

Chapter 2 Machines Help Us Work Machines are tools that help us do work. Think of the kinds of machines you see at a building site. They do work because they lift, push, and pull other objects. To understand how these machines work, you first have to understand simple machines. The Lever Simple machines have few moving parts. An example of a simple machine is a lever. A lever is a bar that moves on a fixed point. The fixed point is called a fulcrum. A seesaw is a kind of lever. On a seesaw, it is easy to move the other person in the air. It would be hard to lift that person yourself. The seesaw is a simple machine that makes lifting someone easier. A seesaw helps you do work, even as you play!

It would take many people to do the work of one power shovel. The power shovel uses a lever to help it lift heavy things. A big scoop is on the end of the lever. When the lever is lowered, the scoop fills with soil. When the lever is raised, it moves up the way a seesaw does. Yet the power shovel lifts soil instead of people. Then the power shovel can turn and drop the soil into a dump truck. The dump truck works like a lever, too. The back of the truck moves on a fixed point, so it is easy to dump the soil. Can you see the lever? By using a lever, the truck can move the soil easily.

Cranes are one of the oldest kinds of machines used for building. Some cranes use a lever to help lift heavy beams high into the air. These levers make it easier for the crane to lift and hold up a heavy weight. The Inclined Plane Another kind of simple machine is an inclined plane. An inclined plane is a flat surface that is raised at one end. A ramp is an inclined plane. This simple machine makes it easier to move things up and down. It helps people in wheelchairs go to different floors of a building without using stairs.