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What is Position in Physics? - Definition & Examples

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  • 0:22 What is Position
  • 0:52 Vectors and Scalars
  • 2:04 Position-Time Graph
  • 2:39 Example
  • 3:23 Lesson Summary
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Lesson Transcript
Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

After watching this video, you will be able to explain what position is, why it is a vector, and interpret position-time graphs. A short quiz will follow.

What is Position?

Where are you right now? How many ways can you answer that question? Maybe you said, 'I'm in front of my computer.' Or maybe you said, 'I'm at home.' If you like to be more precise, you could even give your coordinates on the surface of the earth. There are lots of ways of measuring where you are.

Position is a place where someone or something is located or has been put. In physics, position is usually a number on an axis. You can have an x-axis that looks like this:

The x-axis is circled.
x axis circled on graph

Or a y-axis, like this:

The y-axis is circled.
y axis circled on graph

If you drew these axes on the floor of a room, and then moved to a random place in that room, you would have a position in both the x and y directions. You might be at positive 6 meters in the x-direction and negative 3 meters in the y-direction. That is your position.

Vectors and Scalars

When it comes to position, direction is important. By saying you're at positive 6 meters in the x-direction, you're saying that you are 3 meters to the right of the y-axis. This is a direction.

A number where direction matters is called a vector. A number where direction doesn't matter is called a scalar. For example, temperature is a scalar. Because it never has a direction. The temperature might be 70 degrees F, but it isn't 70 degrees F going up. It might be 40 degrees C, but never 40 degrees C headed west. That's not how temperature works. Temperature is a scalar.

Position is a vector because direction matters. But distance is a scalar. Distance is how far you've traveled. For example, if you run around your room with the axis on the floor, you might run a really long way, until you've gone a total of 50 meters. But your position isn't 50 meters. Your position might be negative 3 meters on the x-axis and positive 4 meters on the y-axis, for example. The direction you ran made no difference to your distance - you still traveled 50 meters. So with distance, direction doesn't matter. Distance is a scalar.

Position-Time Graphs

When your position changes over time, you can show this using a position-time graph. A position-time graph looks like this, with position on the y-axis and time on the x-axis:

Position-time graph
null

If you're not moving, you'll get a flat line, like this:

No movement
flat line on position time graph

If you're not moving at the origin, it will look like this:

No movement at origin
flat line on origin of position time graph

But if you're not moving at a position that isn't the origin, it will look like this:

No movement at a position other than origin
flat line on position time graph

If you're moving at a constant speed, you'll get a diagonal line. If you're moving towards the origin, it will look like this:

Movement towards origin
diagonal line on position time graph

If you're moving away from the origin, it will look like this:

Movement away from origin
diagonal line on position time graph

Example

You need to be able to plot a position-time graph from some data. For example, you might get some data like this:

Data for bicyclist
example data chart

This data shows how a bicyclist changed position over the course of a day, going to work and then back home again. Pause the video and try plotting a graph of this data. I'll show you the solution in a moment.

If you haven't already, pause the video now.

Okay, if you're still listening to the video, you've had a go at plotting the graph. Now I'll show you what it should have looked like. Your graph should look like this:

Position-time graph for bicyclist example
final position time graph for example

The bicyclist went to work at a constant velocity, stayed at the same position for a while because he was at work, and then cycled home. You might even notice that he cycled to work faster than he cycled home. Maybe he was late!

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