p. cm, Includes index, What is work? -- How common are simple machines? -- What is a lever? -- What does a lever do? -- Is a seesaw a lever? -- Are the wheels on my bike a simple machine? -- How do we use wheels and axles? -- What is a pulley? -- How does it work? -- Why do we need pulleys? -- Is a ramp a simple machine? -- What kind of work does an inclined plane help us do? -- Are there other kinds of inclined planes? -- Is doorstop a wedge? -- What are some other wedges? -- What kind of simple machine is a screw? -- How does a screw work? -- Are there other simple kinds of machines? -- How long have people been using simple machines? -- Do we still need simple machines today?