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Newton's Laws of Motion: Test Your Understanding
Teacher's Guide
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Summarize Newton's three laws of motion.
The first law of motion states that a body not acted on by a force moves with constant velocity. The
second law of motion states that the acceleration of a body is proportional to the force acting on it—
and is inversely proportional to its mass. The third law of motion states that two bodies exert forces on
one another that are equal in magnitude but opposite in direction.
In what cases do Newton's laws of motion NOT apply?
Newton's laws of motion do not apply in situations involving speeds near the speed of light or in those
involving atomic or subatomic particles.
Critical Thinking: A space probe is traveling through space far from Earth. The initial forces that launched
the space probe are no longer acting on it, yet the space probe is still accelerating. Does the motion of the
satellite violate Newton's second law? Why or why not?
No, the space probe does not violate Newton's second law. Gravitational forces from nearby celestial
objects now govern changes in the space probe's motion.
Critical Thinking: There exists no way to measure the "absolute" motion of a body. Identify a means of
overcoming this obstacle when applying Newton's laws of motion.
When applying Newton's laws of motion, one must choose an inertial observer. By doing so, someone
can measure motion relative to the specified observer. The accelerations and rotations experienced by
the inertial observer will obey Newton's laws of motion.
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