Why Does a 40kHz Sine Wave on Oscilloscope Screen Appear to Move or Travel?

Hi guys! sorry for this question but I'm stuck in and confused!
I know what's frequency and what's periodic .. my question I entered the lab , I used the oscillator and there on the screen was a wave like function "sin" , I put the frequency as 40KHZ , then on the screen shown that my wave goes so fast (it's like traveling .. ) , what's confused me, how that sin is traveling ? is just frequency make it happen to travel and moving or there's hardware device that gives the wave/sin to look like traveling on the screen? to clear more, is just frequency f enough for letting the wave moving or we need also a hardware device that give a push to the wave/sin to move? if there's no hardware so it's like magic .. just we are configuring the frequency then the wave will move ..
any help?

Ryan,Your description of what you are seeing is a bit confusing. It sounds as if you have an oscillator to create the 40 kHz sin wave and that you may be looking at the result on an oscilloscope.Usually when I see a wave traveling on the screen it is because the oscilloscope is not triggering to the wave to make it stable. The reason you see it moving is that the frequency that the oscilloscope is triggering to is a bit different than your wave. So it's the difference between the two frequencies that causes the wave to move.

Here are some articles to explain how an oscilloscope works.

https://www.explainthatstuff.com/howoscilloscopeswork.html
https://en.wikipedia.org/wiki/Oscilloscope

Hey Ryan,Elizabeth is correct, it sounds like you've set the trigger point too low or it's not set at all.You have two options, press Autoset and this will automatically set up most of the settings you need on your scope (depends on the Oscilloscope you have). If that doesn't work/exist, then you'll have to adjust the trigger level yourself manually.What Oscilloscope (Scope) are you using?If you set the trigger level anywhere between the middle point of the wave and the peak of the wave, it should stop travelling. You should also make sure to select rising edge trigger or falling edge trigger. Don't select the option "rising or falling edge" as this will trigger on either of these. It's best to select one and not both.
Do check out Elizabeth's links for more information, they are invaluable.That should help, Let us know how you get on, -Mike

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