Newton's First Law of Motion—Inertia: The Big Idea

According to the law of inertia, what happens to objects already in motion when no unbalanced forces act on them?

• They speed up

• They slow down until they stop

• They remain in motion

• They change direction randomly

A historical argument against a moving Earth claimed that a bird dropping vertically from a high tree branch could catch a worm only if Earth were at rest. Using Newton's First Law, which explanation best addresses why the bird can still catch the worm even if Earth is moving?

• The bird and worm share Earth's motion, so their horizontal motion continues while the bird drops

• Earth's motion stops when the bird leaves the branch

• Gravity only works if Earth is not moving

• Air resistance cancels all motion on a moving Earth

According to Aristotle, which term describes motion that occurs without any external push or pull, such as a stone falling toward Earth?

• Natural motion

• Violent motion

• Uniform motion

• Accelerated motion

Aristotle classified motion caused by an applied force, like pushing a cart, as _______.

• Violent motion

• Natural motion

• Circular motion

• Uniform motion

Which statement best refutes Aristotle’s claim that Earth must be at rest for everyday motion to occur?

• Objects move only when Earth is still.

• Objects on Earth share Earth’s motion due to inertia, so activities like a bird catching a worm can happen even as Earth moves.

• Air motion cancels Earth’s motion, making objects stationary.

• Gravity stops horizontal motion when Earth moves.

A coin is tossed straight up inside a smoothly moving plane. Which reasoning explains why it lands back in the tosser's hand? Select all that apply.

• The coin keeps the plane’s horizontal motion due to inertia.

• Gravity changes the coin’s horizontal motion to match the plane.

• Only vertical forces act on the coin while it is in the air.

• The plane must be at rest for the coin to be caught.

A passenger flips a coin inside a smoothly cruising airplane. Which statement best explains why the coin appears to move straight up and down relative to the passenger?

• Air pressure forces the coin to stay above the hand.

• The coin shares the airplane’s horizontal velocity due to inertia.

• The window’s shape guides the coin’s path.

• Gravity is absent inside airplanes.

In Taipei’s tallest skyscraper, a more than 3-million-kg steel ball hangs near the top. What is the primary purpose of this massive ball?

• To store extra electrical energy for the building

• To stabilize the building against vibrations from earthquakes or strong winds using inertia

• To measure atmospheric pressure changes at high altitude

• To serve as a decorative centerpiece visible from the street

The law of inertia states that objects already in motion will:

• Continue moving at constant velocity in a straight line unless acted on by a net external force.

• Eventually stop on their own without any external force.

• Change direction automatically after some time.

• Speed up continuously unless stopped by a force.

Identify the first European who effectively challenged the idea, held since Aristotle, that Earth was at the center of the universe.

• Copernicus

• Galileo

• Newton

• Einstein