Newton's First Law

Newton's First Law

Middle School

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Learning Objectives

• Define Newton's First Law of Motion, also known as the law of inertia.

• Explain how unbalanced forces are required to change an object's state of motion.

• Describe the concept of inertia and its relationship to mass.

• Identify real-world applications of Newton's First Law, such as in skateboarding.

Key Vocabulary

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Inertia

An object's tendency to resist any change in its state of motion, whether at rest or moving.

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Force

Any push or pull that has the ability to change an object's state of motion.

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Friction

A force that acts between two touching surfaces and opposes the direction of motion.

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Unbalanced Force

A force that is not canceled out by another force and causes a change in motion.

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The Law of Inertia

• An object at rest will stay at rest unless an unbalanced force acts on it.

• An object in motion will not change its speed or direction on its own.

• This tendency to resist changes in motion is called inertia.

• An object with more mass has more inertia, making it harder to move.

Multiple Choice

Which object has more inertia?

• A small ball

• A large rock

• A paper sheet

• A pencil

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Changing Motion with Forces

• An object's motion changes only when an unbalanced force is applied to it.

• A skateboard at rest has inertia and needs a push to get moving.

• Friction is an unbalanced force that stops the moving skateboard over time.

• Dragging a foot on the ground increases friction to slow down faster.

Multiple Choice

What unbalanced force causes a skateboard to stop rolling on a flat surface?

• Inertia

• Gravity

• Friction

• Mass

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Common Misconceptions

Misconception	Correction
A constant force is needed to keep an object moving.	An object in motion stays in motion due to inertia.
If an object is at rest, no forces are acting on it.	An object at rest can have balanced forces acting on it.
Inertia is a type of force.	Inertia is the resistance to a change in motion, not a force.

Multiple Choice

A hockey puck slides on ice at a constant velocity. How does Newton's First Law explain why it keeps moving with little change in speed?

• The force from the hockey stick is still pushing it.

• Ice has very little friction, so there is almost no unbalanced force to slow the puck down, and its inertia keeps it moving.

• The puck is very light, so it has no inertia.

• The cold temperature of the ice creates a force that propels the puck forward.

Multiple Choice

If you're in a car that stops suddenly, you feel thrown forward. Why does this happen?

• The car's brakes create a forward force on you.

• The car stops, but your body's inertia makes it continue moving forward until a force (like the seatbelt) stops you.

• The air inside the car pushes you forward.

• Your mass suddenly increases, pushing you forward.

Multiple Choice

Two elephants, one large and one small, are at rest. Which one has more inertia and what does this mean if you try to push them?

• The small elephant has more inertia, so it's easier to move.

• The large elephant has more inertia, meaning a larger unbalanced force is needed to make it move.

• They both have the same inertia because they are both at rest.

• The large elephant has less inertia, so it's harder to move.

Multiple Choice

An astronaut in deep space throws a tool. According to Newton's First Law, what path will the tool follow?

• It will eventually slow down and stop as its force runs out.

• It will curve in a circle as it looks for gravity.

• It will travel in a straight line at a constant speed, as there are no significant unbalanced forces acting on it.

• It will stop immediately after leaving the astronaut's hand.

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Summary

• An object's motion will not change unless an unbalanced force acts on it.

• Inertia is an object's resistance to changes in its motion.

• An object's mass is a measure of its inertia; more mass means more inertia.

• Friction is a common unbalanced force that opposes motion.

Poll

On a scale of 1-4, how confident are you about applying Newton's First Law to real-world scenarios?

• 1

• 2

• 3

• 4