# Question on the speed of sound

#### Fiveohhh

##### Diamond Member
I was thinking about this last night... when your in a plane going over the speed of sound and someones sitting behind you, how could you here them if you're traveling faster than sound? wouldn't the sound just trail behind them....? Thanks in advance, this is really bothering me

#### Electric Amish

##### Elite Member
It's all relative.

amish

#### Heisenberg

##### Lifer
The air in the plane is traveling the same speed you are. Do a search for 'intertial reference frames'.

#### tontod

##### Diamond Member
It's all about frame of reference. He is in the same frame of reference as you are. He's also traveling faster than the speed of sound, just like you are.

#### ScoobMaster

##### Platinum Member
.......now if the plane were traveleing at the speed of LIGHT instead and the person behind you switched on a flashlight..........

#### notfred

##### Lifer
It is all relative. Sound inside the airplane is moving relativbe to the airplane, not some arbitrary value of "stopped". Let's assume for the moment that sound always travels at 600mph. you're in an airplane going 650 mph. You say something. Sound eminates from your mouth at 600 mph hour, relative to your body. So, it sounds normal to anyone inside the plane also travelling at 650 mph, however, relative to the ground, your vioce is moving at 1250mph toward the front of the plane, and -50mph (50 mph in the opposite direction) towad the back of the plane.

#### Anubis

##### No Lifer
refrence frames!!!!!!!
YEA Einstein!!!!!!!!!!!!!!!!

for me and others this was the hardest thing to get your head around in Physics

#### conjur

##### No Lifer
Anyone read the recent Discover magazine about black holes and the spin they induce that twists space/time. A good read.

#### Eli

##### Super Moderator | Elite Member
Originally posted by: ScoobMaster
.......now if the plane were traveleing at the speed of LIGHT instead and the person behind you switched on a flashlight..........

#### Fiveohhh

##### Diamond Member
So if you had a vessle moving 1000mph and it was 50yds long the person on the trailering end could say something to the person on the leading edge, and it would sound normal. And what if during that exact moment there was a person at a stand still on the ground in between the two on the vessle(which we'll say is acoustically transparent) won't here it until the trailering edge passes. So in effect the person farther away(at the leading edge) will here it before the person closer? Tried to make that as simple as I could. Thanks again for your help, I'll be able to sleep better now

#### Moonbeam

##### Elite Member
I guess if you had an air gun and could shoot people with a 1000mph blast of air, you would blow their words right out of the air. That would be a different way of silencing people. Could you soundproof your environment with little jets in your ears that blasted air out an 700 plus mph or is it just easier to live in a vacuum like the right.

#### Analog

##### Lifer
Originally posted by: Heisenberg
The air in the plane is traveling the same speed you are. Do a search for 'intertial reference frames'.

#### her209

##### No Lifer
Two words: Doppler Effect

#### BennyD

##### Banned
i think a better way to think of it is to say that sound moves through 200000 air particles per milisecond (not really), so if the air is travelling at 1000mph then the sound will have to travel faster to be travelling at 200000 ap/s.

as the air around the speaker changes, as does the boundaries that govorn how fast the sound travels.