(This article was translated from Japanese to English using DeepL.)

First, a review of the previous lecture.

**To graph a wave, let’s assume that one of the two variables ( t and x) is a constant!**

This was the content of the lecture.

And now that we have actually drawn a graph showing the relationship between *y* and *x* with time *t* as a constant, what would happen to the graph if we considered *x* instead of *t* to be a constant?

## Meaning of *y-t* graph

For moving waves, “taking time *t* as a constant” can be thought of as “taking a picture of the wave”.

So what exactly does it mean to regard *x* as a constant?

As an example, consider a wave created by swinging a rope, where **the value of x represents each point on the rope.**

In other words, “regard

*x*as a constant” means

**“follow only the movement of a single point in the rope”**.

If you are asked to draw a

*y-t*graph at

*x*= 5 m, you can mark the

*x*= 5 m point on the rope and follow the movement of that mark.

**The y-t graph shows the movement of a mark on a medium with time.**

(Note that the y-t graph represents the motion of the medium,

**not the waveform!**)

## Note on wave graphs

Now that we have the two types of wave graphs, look closely at the shape of each graph.

Both the *y-x* and *y-t* graphs have a sinusoidal shape, and **it is impossible to distinguish which graph is which just by looking at the shape!**

**Whenever you see a graph of waves, be sure to check what the horizontal axis represents!**

## Summary of this lecture

## Next Time

Now that we have the two graphs, let’s pay attention to their differences and try to read them!

https://www.yukimura-physics.com/entry/wave-f06