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# Newton's Laws of Motion: Motion in the World Around Us

### Motion in the world around us

#### Newton and the apple tree

Sir Isaac Newton was an English scientist who made discoveries in physics, math, and astronomy. He’s known for the story in which he was sitting under a tree when suddenly, an apple fell on his head.

He wondered why the apple fell down, toward the ground, realizing that there must be an invisible force acting on the apple–the force of gravity. Gravity pulls objects toward the center of the Earth.

Gravity wasn’t his only theory. Newton also came up with the three laws of motion. These laws help us to understand how objects move in the world around us. Check out this video to find out more:

#### Key concepts

Newton's laws analyze how forces act on objects, making them move. Why do cars and bicycles move in the way that they do? What about when you're running or jumping?

To understand these laws, here are three key terms to keep in mind:

• Motion: Motion occurs when an object moves from one place to another or changes positions. A duck waddling from Point A to Point B, and then lowering its head to drink, are two forms of motion.
• Force: Force is needed for any action that causes an object to move or change its shape. If you lift a box off of the floor, you’re using force to move it. If you lean on the box, you’re also exerting force.
• Acceleration: The rate at which an object speeds up or slows down–like a car or a bike–is referred to as acceleration. (As a side note, acceleration depends on velocity, or the actual speed, and the time it takes for an object to make this change).

An overview of the three laws

In this tutorial, we’ll get into the details of each law to understand how they work. For now, here are some examples of these laws in action:

1. The first law of inertia explains why a stone on the ground remains still, unless something or someone moves it.
2. The second law about force helps us to understand why a bike needs less force to move than a car, since the car is heavier than the bike.
3. The third law of action and reaction tells us why when you throw a ball against a wall, it bounces.