# Can sound be accelerated?

If I were riding my motorbike, at say 50 kph, and then at a particular point shouted out my name, theoretically speaking, would my voice reach a person standing, say 50 m ahead, at the same time as it would as if I were standing at that same point and shouting?

In other words, would the sound waves be affected by my momentum? And if sound waves can indeed be accelerated, can they also be decelerated (not halted entirely, but delayed in some way)?

The sound won’t get to its destination any sooner, but its pitch will change. Think of the sound of a train whistle as it passes you – higher pitched as it approaches, lower pitch as it heads away.

No. Sound travels at a speed determined by the medium in which it is being carried. Once created and on their way, the sound waves don’t know what speed the object creating them was travelling at. Your shout may be doppler-shifted by your speed (appearing shorter and at a higher frequency to an observer in front of you), but the time it takes to get to them won’t be changed by how fast you were moving.

The time taken will be the same, but the frequency of the sound waves will change. Google on the Doppler effect.

The time taken will be the same, but the frequency of the sound waves will change. Google on the Doppler effect.

(After waiting twenty minutes for the server to accept my post, I see on preview that your question’s been answered, but still suggest you look up the term “Doppler effect”.)

Sound waves can accelerate if the medium increases in density, like say a colder denser bubble of air. Likewise they can be slowed by a less dense medium or stopped by a vacuum.

Sound waves can accelerate if the medium increases in density, like say a colder denser bubble of air. Likewise they can be slowed by a less dense medium or stopped by a vacuum.

Now, if you happened to have a 50KPH tailwind moving the air along with you as you were moving, then the sound would appear accelerated relative to a stationary observer. It’s the speed of the carrying medium which determines it.

Great… thanks for clearing that up!! Another related question that came to my mind after reading some of the replies…

## Quote:

It’s the speed of the carrying medium which determines it.

Would the same apply to radio waves too?
For example, suppose I had this spaceship currently in the vicinity of Jupiter and making its way to Saturn, and I wanted to send it an urgent instruction, would accelerating my transmitter to a certain velocity and THEN sending out the radio signal cause the signal to get there any faster, and could my signal be distorted in any way because of the acceleration? It being space, there wouldn’t be any scope for variation in the physical properties of the transmitting medium. Also assuming all the intermediate planets weren’t in the way.

Radio waves travel at the speed of light, so interesting relativity effects occur. The radio waves appear to be moving at the speed of light relative to you as well as to the observer.

Electromagnetic Radiation (radio waves, light, X-Rays, etc.) doesn’t propagate via any medium, first off (passing through a medium slows it however, or more correctly, causes it to be absorbed and re-emitted, which slows the overall signal). Travelling in the direction you’re sending the EM waves will increase their frequency (blueshift). The speed of electromagnetic radiation is a constant. One of the central findings of relativity is that you cannot add your speed to the speed of light you’re emitting.

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radio is light wave. light travels at the speed of light irrespective of the ship velocity. It would slow down slightly if it moved into a denser medium however

here’s a good explanation of the doppler shift and an answer to your question…

“Doppler shift occurs when sound is generated by, or reflected off of, a moving object”

“Doppler shift in the extreme creates sonic booms”

and the master has spoken on a related topics:

What would happen to sound if I traveled at Mach 1?

If you turn on your headlights while driving at the speed of light, what happens?

If I fire a gun while near light speed, will the bullet EXCEED light speed?

and, welcome to the boards, gouda