12.2 Newton's First and Second Laws of Motion
Reading Strategy
Key Concepts
How does Newton's first law relate change in motion to a zero net force?- How does Newton's second law relate force, mass, and acceleration?
- How are weight and mass related?
Vocabulary
inertia
mass
weight
Reading Strategy
Building Vocabulary Copy the table below. Then as you read the section, write a definition for each vocabulary term in your own words.
| Vocabulary | Definition |
|---|---|
Inertia |
a. |
b. |
c. |
d. |
e. |
Why do some cars accelerate faster than others? How does an ice skater glide far across the ice after pushing off only once? The answers to these questions involve the concepts of mass and inertia.
Aristotle, Galileo, and Newton
Modern scientists understand the relationships between force and motion. However, it took about 2000 years to develop this understanding.
Aristotle
The ancient Greek scientist and philosopher Aristotle (384 B.C.–322 B.C.) made many scientific discoveries through careful observation and logical reasoning. He was not always correct. Aristotle incorrectly proposed that force is required to keep an object moving at constant speed. This error held back progess in the study of motion for almost two thousand years.
Galileo
Italian scientist Galileo Galilei (1564–1642) experimented to find out about the world. By rolling balls down wooden ramps, he studied how gravity produces constant acceleration. Galileo concluded that moving objects that were not subjected to friction or any other force would continue to move indefinitely. Galileo's portrait and the title page from the book that presented his work are shown in Figure 10.
Figure 10
Galileo's work helped correct misconceptions about force and motion that had been widely held since Aristotle's time.
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