What does Newton's First Law state?

Force equals mass times acceleration Every action has an equal and opposite reaction An object remains at rest or moves at constant velocity unless a net force acts on it Objects always slow down because gravity pulls on them

What is inertia?

The force that keeps planets in orbit The tendency of an object to resist any change in its state of motion The energy stored in a stationary object The friction between two surfaces

A hockey puck slides across an ice rink and gradually slows to a stop. Which best explains why it stops?

Moving objects naturally run out of motion over time The puck's inertia decreases as it moves Friction from the ice surface and air resistance apply an unbalanced force that slows the puck Gravity pulls the puck backward as it moves away from the player

You are sitting in a car that suddenly brakes. Your body lurches forward. What best explains this?

A forward force from the engine pushes you forwards during braking Gravity suddenly increases when the car slows down Your body's inertia keeps it moving forward while the car decelerates The brakes push air forward, which then pushes your body

Galileo Galilei contributed to the idea behind Newton's First Law. What was Galileo's key insight?

Heavy objects fall faster than light ones, proving they have more inertia Forces always come in pairs of equal size and opposite direction If surfaces were perfectly smooth (frictionless), a moving object would never slow down on its own Gravity pulls objects forward as well as downward

Which object has the most inertia?

A tennis ball A feather A bicycle A fully loaded cargo ship

An astronaut in deep space — far from any planet — gives a rock a push and lets go. What happens to the rock?

It gradually slows down and stops after a while It speeds up because there is no friction to slow it down It curves because of Earth's gravity even in deep space It continues moving in a straight line at constant speed forever

Why is it important that Newton's First Law includes the phrase 'in the same direction'?

Because direction is the same as speed in physics Because a force is needed not just to change speed but also to change direction Because objects always move in circles unless a force stops them Because gravity always pulls things in the same direction as their motion

Aristotle believed that objects naturally come to rest and need a constant force to keep moving. Why was he wrong?

He was correct — forces are always needed to maintain motion He did not account for friction — the real reason objects slow down and stop He did not know about gravity, which provides the force to keep things moving Objects do naturally come to rest — Newton only corrected the reason

A tablecloth is pulled sharply from under plates and glasses on a table. The dishes barely move. What principle explains this trick?

Gravity holds the plates down so strongly that no horizontal force can move them Inertia — the dishes resist the sudden change in motion and tend to stay where they are Air pressure from above pushes the plates down onto the table The normal force from the table cancels the frictional force from the cloth