Why is a reference point needed to determine motion?

Answer 1

Without the reference point, there is no motion. If both you and a bird are moving at

30 mph, then that bird is not in motion unless there is some other point of reference.

To you, it would appear that the bird is stationary, and the world around you and the

bird are moving.

Motion has nothing to do with speed. Motion is the difference between an object and

a reference point. If you are moving at 30 mph, and the bird is moving at 35 mph, then

without an outside reference point, the bird is in motion of 5 mph relative to you.

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Another example:

You're sitting in a comfortable chair, reading a book. That would be hard to do if the

book were moving, but it isn't. It's just sitting there in your lap, perfectly still. If you

nod off and let go of the book, it just lays there. It doesn't go anywhere.

Except that you happen to be a passenger on an airliner that's flying 35,000 feet

above the ground at 400 miles per hour. Anybody on the ground who happens to

notice would swear that you and the book are both moving at 400 mph.

You say the book isn't moving at all, the guy on the ground says the book is moving

at 400 mph. You're both correct, because you have different references.

The speed of motion, the direction of motion, and whether there even is any motion at all,

they all depend on your reference. There's no such thing as 'real' speed or 'real' motion.

Answer 2

A reference point is needed to determine motion because motion is relative and depends on what is used as a point of comparison. Without a reference point, we cannot accurately describe the movement of an object. By choosing a stationary reference point, we can establish whether an object is moving, in what direction, and at what speed.