PrepGo

AP Physics 1: Algebra-Based Practice Quiz: Newton's Third Law

Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026

Test your understanding with short quizzes. This quiz has 11 questions to check your progress.

Question 1 of 11

According to Newton's third law, how are the paired forces that two interacting objects exert on each other characterized?

All Questions (11)

According to Newton's third law, how are the paired forces that two interacting objects exert on each other characterized?

A) They are equal in magnitude and opposite in direction.

B) They are equal in magnitude and in the same direction.

C) The force on the larger object is greater than the force on the smaller object.

D) The forces act on the same object to achieve equilibrium.

Correct Answer: A

The content states that Newton's third law describes the interaction of two objects in terms of paired forces. The fundamental principle of these pairs is that they are equal in magnitude and opposite in direction, each acting on one of the two interacting objects.

A book is resting on a tabletop. The Earth exerts a gravitational force on the book. Based on Newton's third law, what is the corresponding reaction force to this gravitational pull?

A) The normal force exerted by the table on the book.

B) The gravitational force exerted by the book on the Earth.

C) The frictional force between the book and the table.

D) The net force on the book, which is zero.

Correct Answer: B

Newton's third law describes the interaction between two objects. The initial force is the Earth acting on the book. The paired force must therefore be the book acting on the Earth. The normal force is part of a different interaction pair (table on book / book on table).

Two astronauts are floating in space. Astronaut 1 pushes Astronaut 2 away. If the system is defined as both astronauts together, how does this interaction affect the system's center of mass?

A) The center of mass accelerates in the direction Astronaut 2 moves.

B) The center of mass accelerates in the direction Astronaut 1 moves.

C) The motion of the system's center of mass is not influenced.

D) The center of mass moves to a point midway between the two astronauts.

Correct Answer: C

The forces the astronauts exert on each other are internal to the two-astronaut system. The provided content explicitly states that 'Interactions between objects within a system (internal forces) do not influence the motion of a system's center of mass.'

What term describes the macroscopic net result of forces that segments of a cable exert on each other when it is used to pull a car?

A) Weight

B) Friction

C) Tension

D) Normal Force

Correct Answer: C

The content defines tension as 'the macroscopic net result of forces that segments of a string, cable, chain, or similar system exert on each other in response to an external force.'

For an ideal string being pulled from both ends, how does the tension at the center of the string compare to the tension at either end?

A) It is half the tension at the ends.

B) It is double the tension at the ends.

C) It is the same as the tension at the ends.

D) It is zero.

Correct Answer: C

The provided content states, 'The tension in an ideal string is the same at all points within the string.' Therefore, the tension is uniform throughout its length.

A large truck and a small car collide head-on. During the collision, which statement correctly describes the paired forces of the interaction?

A) The truck exerts a greater force on the car because it has more mass.

B) The car exerts a greater force on the truck because it experiences greater acceleration.

C) The truck and car exert forces of equal magnitude on each other.

D) The net force on the truck-car system is zero.

Correct Answer: C

According to Newton's third law, the interaction between two objects involves paired forces that are equal in magnitude and opposite in direction. The mass of the objects does not change the magnitude of the interaction forces they exert on each other.

A cannon fires a cannonball. If the system is defined as ONLY the cannonball, what is the nature of the force exerted by the cannon on the cannonball?

A) It is an internal force that does not affect the cannonball's motion.

B) It is an external force that causes the cannonball's center of mass to accelerate.

C) It is an internal force that is paired with the cannonball's gravity.

D) It is a paired force that is cancelled by the force of the cannonball on the cannon, resulting in no acceleration.

Correct Answer: B

Since the system is defined as only the cannonball, the cannon is external to the system. The force from the cannon is therefore an external force that acts on the system (the cannonball), causing its center of mass to accelerate. The concept of internal forces not affecting the system's motion only applies if both the cannon and cannonball were included in the system.

Newton's third law is fundamentally a description of:

A) The motion of a single object under a net force.

B) The interaction of two objects.

C) The properties of an ideal string.

D) The conservation of energy in a system.

Correct Answer: B

The content begins by stating, 'Newton's third law describes the interaction of two objects in terms of the paired forces that each exerts on the other.'

A spider is climbing up its silk thread at a constant velocity. The forces exerted by the segments of the thread on each other are best described as:

A) Internal forces that result in tension.

B) External forces that change the thread's center of mass.

C) Paired forces equal to the spider's weight.

D) Unbalanced forces causing the thread to accelerate.

Correct Answer: A

The content defines tension as the 'macroscopic net result of forces that segments of a string...exert on each other'. These are internal forces within the thread itself, responding to the external force of the spider pulling on it.

A person stands in a canoe and throws a package forward onto a dock. If the canoe, person, and package are considered a single system, what is the effect of the person throwing the package?

A) The motion of the system's center of mass is unaffected by this action.

B) The system's center of mass accelerates forward with the package.

C) The system's center of mass accelerates backward as the canoe moves.

D) The tension in the canoe causes the center of mass to remain stationary.

Correct Answer: A

The act of throwing the package involves forces between the person and the package. Since both are part of the defined system, these are internal forces. The content states that 'Interactions between objects within a system (internal forces) do not influence the motion of a system's center of mass.'

Which of the following is the best representation of a paired force interaction as described by Newton's third law?

A) The force of gravity on a satellite and the centripetal force keeping it in orbit.

B) The force of a bat hitting a ball and the force of the ball hitting the bat.

C) The upward tension in a rope and the downward force of gravity on a suspended mass.

D) The forward push of a car's engine and the backward force of air resistance.

Correct Answer: B

Newton's third law describes the paired forces between two interacting objects. The force of the bat on the ball and the force of the ball on the bat is a direct example of such an interaction pair. The other options describe multiple forces acting on a single object or forces that are not part of a direct interaction pair.