Physics Lesson 3.13.1 - What is Relative Motion?

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Welcome to our Physics lesson on What is Relative Motion?, this is the first lesson of our suite of physics lessons covering the topic of Relative Motion, you can find links to the other lessons within this tutorial and access additional physics learning resources below this lesson.

What is Relative Motion?

So far, we have discussed situations involving motions whose kinematic quantities were measured starting from a fixed location known as "reference point (frame)" or "origin." It means the origin was presumed as unmoveable.

But happens if the origin is not stationary? It is obvious the values of kinematic quantities will not be the same as if origin was stationary. In fact, everything in the universe is moveable. Hence, the approach with moveable origin is more realistic than that with stationary one.

In this tutorial, we will discuss about the relationship between the kinematic quantities when the reference point is not stationary. The motion involved in such cases is known as "relative motion."

To help readers understand this point as easier as possible, let's answer to the questions posed in the "Introduction" paragraph.

1. In the first question, we can say that if the actual position of our body is taken as reference frame, then we are at rest. However, for somebody who is watching us from outside the Earth, for example from a satellite, we are moving (rotating) together with the Earth. Therefore, it depends on the reference frame chosen saying whether we are moving or not.
2. It is obvious for a person who is sitting under a tree, we are moving together with our car past the trees. However, if we chose the reference frame any object inside our car, it seems the trees are moving in the opposite direction of ours.
3. If we take our actual position as a reference point (frame), we say the Sun moves from East to West. However, we know this does not occur due to the Sun movement (which takes place in any case), but because of the Earth's rotation around its axis from West to East. Therefore, if we take the Sun as a reference point (frame), we say it the Earth that is moving, not the Sun.

As seen in the above examples, the motion of an object does not depend only on the values of its kinematic quantities but also on the reference frame chosen to study its motion. Therefore, we say "the motion is relative; its parameters may be different in two different reference frames although the rhythm of motion may be the same."

For simplicity, in this tutorial we will focus purely on one-dimensional motions as the same approach can also be used for two and three-dimensional motion as well; only the mathematical apparatus becomes more complex.

You have reach the end of Physics lesson 3.13.1 What is Relative Motion?. There are 7 lessons in this physics tutorial covering Relative Motion, you can access all the lessons from this tutorial below.

More Relative Motion Lessons and Learning Resources

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Enjoy the "What is Relative Motion?" physics lesson? People who liked the "Relative Motion lesson found the following resources useful:

1. Defintion Feedback. Helps other - Leave a rating for this defintion (see below)
2. Kinematics Physics tutorial: Relative Motion. Read the Relative Motion physics tutorial and build your physics knowledge of Kinematics
3. Kinematics Revision Notes: Relative Motion. Print the notes so you can revise the key points covered in the physics tutorial for Relative Motion
4. Kinematics Practice Questions: Relative Motion. Test and improve your knowledge of Relative Motion with example questins and answers
5. Check your calculations for Kinematics questions with our excellent Kinematics calculators which contain full equations and calculations clearly displayed line by line. See the Kinematics Calculators by iCalculator™ below.
6. Continuing learning kinematics - read our next physics tutorial: Motion. Types of Motion

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Kinematics Calculators by iCalculator™

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