Understanding Newton's First Law

Which of the following best describes Newton's First Law of Motion?

• An object will change its state of motion only if a force is applied.

• An object will always remain in motion regardless of any forces.

• An object will stop moving if no force is applied.

• An object will move faster if no force is applied.

Answer explanation

Newton's First Law states that an object will not change its state of motion unless a force acts on it. Therefore, the correct choice is that an object will change its state of motion only if a force is applied.

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DOK Level 2: Skill/Concept

If a book is lying on a table and remains at rest, which of the following statements is true according to Newton's First Law?

• The book is in motion.

• There is no force acting on the book.

• The forces acting on the book are balanced.

• The book is accelerating.

Answer explanation

According to Newton's First Law, an object at rest remains at rest unless acted upon by an unbalanced force. Since the book is at rest, the forces acting on it must be balanced, making this the correct statement.

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DOK Level 2: Skill/Concept

A soccer ball is rolling on the ground and eventually comes to a stop. Which force is primarily responsible for stopping the ball?

• Gravity

• Friction

• Air resistance

• Magnetism

Answer explanation

Friction is the primary force that opposes the motion of the soccer ball as it rolls on the ground. It acts between the ball and the surface, gradually slowing it down until it comes to a stop.

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DOK Level 2: Skill/Concept

A car is moving at a constant speed on a straight road. According to Newton's First Law, what will happen if no additional forces act on the car?

• The car will speed up.

• The car will slow down.

• The car will continue moving at the same speed.

• The car will stop immediately.

Answer explanation

According to Newton's First Law, an object in motion stays in motion at a constant speed unless acted upon by an external force. Since no additional forces are acting on the car, it will continue moving at the same speed.

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DOK Level 2: Skill/Concept

Explain why passengers in a car lurch forward when the car suddenly stops.

• Because the car is accelerating.

• Because of the passengers' inertia.

• Because of the car's engine.

• Because of the road's friction.

Answer explanation

Passengers lurch forward when the car suddenly stops due to inertia, which is the tendency of objects to resist changes in their state of motion. When the car halts, the passengers continue moving forward.

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DOK Level 3: Strategic Thinking

A hockey puck slides on ice and eventually comes to a stop. Which concept from Newton's First Law explains this observation?

• The puck's inertia increases.

• An unbalanced force (friction) acts on the puck.

• The puck's mass decreases.

• The puck's velocity increases.

Answer explanation

The puck comes to a stop due to an unbalanced force, specifically friction, acting against its motion. According to Newton's First Law, an object in motion will stay in motion unless acted upon by an external force.

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DOK Level 3: Strategic Thinking

A spacecraft is moving in space far from any planets or stars. What will happen to its motion if no external forces act on it?

• It will stop moving.

• It will change direction.

• It will continue moving at the same speed and direction.

• It will accelerate.

Answer explanation

According to Newton's first law of motion, an object in motion will remain in motion at a constant speed and direction unless acted upon by an external force. Therefore, the spacecraft will continue moving at the same speed and direction.

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DOK Level 2: Skill/Concept

Why is it important for a seatbelt to be worn in a moving vehicle, according to Newton's First Law?

• To increase the vehicle's speed.

• To provide a force that stops passengers from continuing in motion when the vehicle stops.

• To decrease the vehicle's inertia.

• To make the vehicle more comfortable.

Answer explanation

According to Newton's First Law, an object in motion stays in motion. A seatbelt provides the necessary force to stop passengers from continuing forward when the vehicle suddenly stops, preventing injury.

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DOK Level 3: Strategic Thinking

A ball is thrown straight up into the air. At the highest point, what can be said about the forces acting on the ball?

• There are no forces acting on the ball.

• The forces are balanced.

• Gravity is the only force acting on the ball.

• The ball is in motion due to inertia.

Answer explanation

At the highest point, the ball is momentarily at rest before falling back down. Gravity is the only force acting on it, pulling it downward, while no other forces counteract this, making it the correct choice.

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DOK Level 3: Strategic Thinking

Which of the following scenarios is an example of Newton's First Law in action?

• A car accelerating on a highway.

• A book sliding off a tilted table.

• A ball remaining at rest on the ground.

• A rocket launching into space.

Answer explanation

Newton's First Law states that an object at rest stays at rest unless acted upon by an external force. A ball remaining at rest on the ground exemplifies this law, as it does not move without an external force acting on it.

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DOK Level 2: Skill/Concept