Motion is the act of moving and plays a huge role in the study of physics.

This lesson walks through important terms and the laws of motion that guide the study of motion.

## Motion and Terms

**Motion** is the process of something moving or changing place, or even just changing position.There are a lot of factors involved every time something moves.

There are fewer factors involved if an object moves at the same speed in a straight line. However, most movement involves changing the speed of the movement and changing directions. Here is a list of terms that go hand in hand with learning about motion:**Speed** is how long it takes for an object to travel a certain distance. Its formula is distance divided by time, or *d/t*. A car’s speed is often measured in how many miles it can travel in an hour. So the distance is miles and the time is hours (distance/time = Miles/Hour, or Miles per Hour, or mph).**Velocity** and speed are very close and often mixed up.

They both measure *d/t*. Velocity adds an extra step; it measures distance over time or speed in a given direction. So a car’s speed could be 55 mph, but its velocity would be 55 mph in a northward direction.

**Acceleration** is when any part of an object’s velocity changes. If the object speeds up or travels over a given distance in a shorter amount of time, then there is acceleration. There can also be acceleration if an object changes direction.

So even if the car continues to travel at the speed of 55 mph but turns and heads in an eastward direction, it is still accelerating.**Force** is any type of a push or pull. In order for an object to accelerate, it needs to have a force acted upon it. In other words, in order for an object to change speed or direction, it needs to be pushed or pulled.**Mass** is the amount of matter that something is.

It is usually measured in grams.

## Newton’s Laws of Motion

**Sir Isaac Newton** is the scientist whose ideas and laws have led to modern day physics and the study of motion. Newton lived from 1643-1727. He was knighted for his ideas about motion, gravity, and more. During his studies he came up with three laws of motion.**Newton’s First Law of Motion** is that an object will stay at rest or remain in uniform motion (constant velocity) unless acted upon by a force.

Inertia is an object’s resistance to move; therefore this law is often referred to as the law of inertia.Basically, this explains that if an object is traveling at a constant speed in the same direction, it will continue to move at the same speed in the same direction unless it is pushed or pulled by something. This law is easier to think about if you pretend gravity does not exist. Picture rolling a marble in a gravity-free environment – the marble will continue to roll unless something either pushes it or pulls it and either slows it down, speeds it up, or changes its direction of travel.**Newton’s Second Law of Motion** is that the force acting on an object is directly related to the acceleration and mass of the object to which the force is being applied. It is summed up in the equation: *F = ma* or the net force = mass of the object x the acceleration of the object.The second law shows that the amount of force needed to place an object in motion or to make it change positions relates to its mass and the acceleration of the object.

This is probably why they named the SI unit for force a newton.1 newton = 1 kg;m/s2**Newton’s Third Law of Motion** says that when one object exerts a force on another object, the second object exerts a force of the same magnitude back on the first object in the opposite direction. This law is more clearly stated as: For every action there is an equal and opposite reaction.This law can be explained with every step you take. Every time you take a step, your foot is pushing (action 1) down on the ground.

At the same time, the ground is pushing (action 2) up (opposite of down) on your foot, allowing for you to move.

## Lesson Summary

**Motion** is the act of moving or changing position. When studying motion there are many factors to look at. The main factors of motion revolve around force, speed, velocity, acceleration, and an object’s mass.

Sir Isaac Newton made many observations and gave us three Laws of Motion to help us better understand how objects move. **Newton’s First Law of Motion** is that an object will stay at rest or remain in uniform motion (constant velocity) unless acted upon by a force. **Newton’s Second Law of Motion** is that the force acting on an object is directly related to the acceleration and mass of the object to which the force is being applied. **Newton’s Third Law of Motion** says that when one object exerts a force on another object, the second object exerts a force of the same magnitude back on the first object in the opposite direction. This law is more clearly stated as: For every action there is an equal and opposite reaction.

## The Factors of Motion

**Force**: any type of push or pull exerted on an object**Speed**: how long it takes for an object to travel a certain distance**Velocity**: measures distance over time or speed in a direction**Acceleration**: change in velocity**Mass**: amount of matter something is

## Learning Outcomes

When you are finished, you should be able to:

- Define motion
- Identify the factors of motion
- State Newton’s Laws of Motion