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Related Resources

Principles of Aeronautics:
Forces and Motion

Lesson plans and experiments
that illustrate Newton's
laws of motion.

How Bumper Cars Work

A lesson on how bumper cars work.

Newton and the Laws of Motion


Most people know Sir Isaac Newton for his discovery of gravity, which is thought to have been triggered when he watched an apple drop from a tree. But Newton was also responsible for laying down the fundamental laws of the physical universe: the principles that describe not only how things work but why. These principles are his laws of motion, and they built on the work of great scientific minds who came before him.

Newton was born in Lincolnshire, England, in 1642, only a few years after the death of Galileo Galilei. He showed no particular talent for farming (his family's line of work), but a true genius for mathematics. Building on the work of predecessors such as Galileo, Copernicus, and Kepler, he laid out the principles of his laws of motion, the universal theories that tied the work of these great minds together. He once confessed, "If I have seen further than other men, it is because I stood on the shoulders of giants."

Newton was insecure, badtempered, and sometimes reclusive--not exactly the friendly figure of folklore who was charmed by the fall of an apple. But he explained the physical laws that allow us to walk on the moon and build ever more exciting amusement parks. These are the laws of motion he laid down:

The First Law of Motion: The Law of Inertia
Newton's first law expanded on the work of Galileo. This well-known law states that bodies in motion tend to stay in motion, unless they are acted on by an external force. Also, bodies at rest tend to stay at rest, unless they are acted upon by an external force.

This law governs why a driver is thrown forward in a head-on automobile accident. The car may have stopped, but the driver continues moving forward unless held in place by a seatbelt.

The Second Law of Motion: The Law of Acceleration
Newton's second law explains how the mass of an object and the amount of force applied to an object are related to acceleration. In brief, it says that the greater the mass of an object, the more it resists being moved and therefore the smaller its acceleration will be. It also says that the greater the force applied to an object, the greater the object's acceleration will be.

To understand this law, imagine pushing a pebble, and then imagine pushing a boulder. The pebble has a smaller mass, and so will accelerate faster than the boulder will. Now imagine pushing a boulder with your bare hands and then imagine pushing it with a powerful backhoe. The backhoe is able to exert more force on the boulder, and so will make it accelerate faster than when you pushed it with your bare hands.

The Third Law of Motion: The Law of Interaction
Newton's third law explains how objects interact with other objects. It's based on the idea that every action produces an equal and opposite reaction. But what does this really mean?

Think about the bumper cars. When you hit another car, you exert a force on that car. That's not the end of it, though. Even if you hit a car that is at rest, that car is also exerting a force on you. These forces are opposite, or moving in different directions from each other.

Here's another example. When you jump up in the air, you must first propel yourself by pushing away from the earth (or in other words, pushing the earth away). You can't perceive it, but the earth responds by pushing you away from it. Both your push against the earth and the earth's equal and opposite push against you propel you into the air.

[Back to Bumper Cars]   [Next: Free Fall]


"Amusement Park Physics" is inspired by programs from The Mechanical Universe...and Beyond.


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