Machines
Let’s Ride a Bike!
This book examines the simple machines in bicycles and how they work together
to make a bicycle move. This book is written at the middle of three reading levels.
FOCUS Book
Connections to Next Generation Science Standards
Science and Engineering Practices
Constructing Explanations and Designing Solutions
Obtaining, Evaluating, and Communicating Information
Disciplinary Core Ideas
PS2.B: Types of Interactions
Objects in contact exert forces on each other.
PS3.A: Definitions of Energy
The faster a given object is moving, the more energy it possesses.
Crosscutting Concepts
Energy and Matter
Energy can be transferred in various ways and between objects.
Performance Expectations
3-PS2-1. Plan and conduct an investigation to provide evidence of the effects of balanced and unbalanced forces
on the motion of an object.
4-PS3-4. Apply scientific ideas to design, test, and refine a device that converts energy from one form to another.
Enriching Vocabulary
You may want to introduce these terms to students before they read the book.
drive chain
a pulley system with a chain that wraps around a gear
friction
the force that builds up when objects rub against each other
lever
a simple machine with a rigid bar that turns around a fulcrum
sprocket
a gear that has teeth to hold a chain
work
the act of using force to move something over a certain distance
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Machines—Let’s Ride a Bike!
FOCUS Book teaching tips
Read-Think-Write Answer Key
1. Why did high-wheel bikes replace velocipedes?
The velocipede was slow and painful to ride. High-wheel bicycles were more comfortable
and faster to ride.
2. How is the front wheel on a high-wheel bike similar to the front sprocket
on a modern road bike?
The front wheel of a high-wheel bike and the front sprocket on a modern road bike both work to increase
speed. By turning a larger wheel or sprocket in front, the smaller back wheel or sprocket turns more
times, helping the bike travel faster, with less work applied.
3. Look at the diagram on page 9. Why do some bikes have so many sizes of sprockets?
The sprockets are different sizes to allow the rider to change gears. Lower gears make it easier to pedal
when climbing hills. Higher gears allow the rider to pedal less while keeping the same speed, or to travel
faster when pedaling at the same rate.
4. The tires on a racing bike that rides on paved roads are most likely
.
(b) narrow and smooth
5. If you were designing a new kind of bike, how would you use or limit friction to make your
bike function better?
Answers will vary based on a student’s design, but should demonstrate an understanding of friction
and the features that make use of it as described in the book. Friction is important when starting and
stopping. Tires are designed with some amount of friction to grab the riding surface. Brake pads apply
friction to the wheel rims. Some bike parts, such as an oiled chain and smooth tires, are designed to
limit friction so that they move smoothly and easily.
FOCUS Question Suggested Response
How do the parts of the bicycle work together to make it move and stop? Discuss the simple
machines found in a bicycle and how they work together to make the bicycle move.
Answers will vary based on the simple machines the student identifies. Examples of simple machines
found in a bicycle are gears, levers, and wheels and axles. Gears are used in the drive chain. The
handlebar is a lever that is used to steer the bicycle. The wheels have axles that run through their
centers that allow them to rotate. Students might identify other examples.
BE A SCIENTIST! TEACHING SUPPORT
Gears working together produce a mechanical advantage. In bicycles, gears make riding up hills easier
and allow the rider to pedal faster with less work. Use the attached gear outlines to create a set of three
templates on stiff paper or poster-board material. Then have students make their own gears out of foam or
cardboard. Supervise students as they cut through the thick material, or precut them for the class. Each
student or group should start with two gears of different sizes. Later, encourage students to experiment by
creating three or more gears of different sizes to discover how they move together.
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Machines—Let’s Ride a Bike!
FOCUS Book teaching tips
Gear Template
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Machines—Let’s Ride a Bike!
FOCUS Book teaching tips
Gear Template
Page 2 of 2
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