What is Motion? - Definition & Laws

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  • 0:05 Motion and Terms
  • 2:03 Newton's Laws of Motion
  • 4:28 Lesson Summary
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Lesson Transcript
Kelly Robson

Kelly has taught High School Science and Applied Communications. She holds an Education Specialist Degree in Ed. Leadership.

Expert Contributor
Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

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.

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Additional Activities

Examples of Motion

In this real world application, students will be analyzing some activity in their life and looking for the different types of motion outlined in the lesson. For example, students might choose to look at an airplane taking off. They would describe the speed of the airline and include the direction to describe the velocity. They could explain that the airplane's velocity increases as it takes off, which gives it acceleration. They could also explain that the engines provide the force to move the airplane forward and discuss the mass of an average airplane.

Student Instruction

In this activity you'll be analyzing an activity to look for the different types of motion explained in the lesson. For example, you might analyze an airplane taking off, or a track star running a mile. For your final product you'll be creating a poster that has an image of the motion and your explanation for each property around the sides. To make sure your poster has everything you need, refer to the criteria for success below.

Criteria For Success

  • Poster includes a colorful image of one activity
  • Poster includes a description of how the activity has all of the following vocabulary words about motion like: speed, velocity, acceleration, force and mass
  • Poster is colorful, attractive and professionally designed
  • Student can explain why the activity has different types of motion

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