[ 3 / biz / cgl / ck / diy / fa / ic / jp / lit / sci / vr / vt ] [ index / top / reports ] [ become a patron ] [ status ]
2023-11: Warosu is now out of extended maintenance.

/sci/ - Science & Math

View post   
File: 6 KB, 473x454, ponder guy.png [View same] [iqdb] [saucenao] [google]
4849164 No.4849164 [Reply] [Original]

Ok quick stupid question.


An object is moving at constant velocity in the x direction and for some reason, it drops some of its mass in the y direction without any external force making it accelerate. It WILL stay inert, right? Bit its momentum would have changed.

But what about impulse? There must have been an impulse if its momentum changed, right? Where was the force and where was the time? Is it necessary that a force affect something with a decreasing mass?

>> No.4849193

Well if it drops in the y direction vertically (which wouldn't naturally happen, it would still have velocity in the x direction) then you can figure out the new speed of the mass going in the x direction because momentum is conserved

>> No.4849194

bump

>> No.4849197

>>4849193
It could. Imagine a jet plane dropping a bomb or something.

But anyway, yes. I understand that it would retain its velocity in the x direction, and it would behave pretty much like a projectile, but what about its impulse? Where's the F and the t?

>> No.4849205

>>4849164
>But its momentum would have changed
No, it wouldn't have.

>> No.4849210

>>4849205
No? But isn't there a change in mass? And it's moving.

>> No.4849216

>>4849210
a. How could something lose mass moving in the y direction?
b. Momentum doesn't necessarily have to be the product of mass and velocity (Photons, which are massless, have momentum).

>> No.4849228

The momentum of the system object + shit it threw is conserved, the momentum of the ibject itself, not.

>> No.4849226
File: 287 KB, 650x854, 1326951693986.jpg [View same] [iqdb] [saucenao] [google]
4849226

>>4849197
Its momentum does change, because of the force of gravity. And what is force again? F = dp/dt

>> No.4849232

>>4849216
Forget a, but b still applies.

>> No.4849233

>>4849226
>it drops some of its mass in the y direction without any external force making it accelerate

Learn to read

>> No.4849236

I'm not asking for the conservation of momentum. I'm asking for Impulse-Momentum theorem. There's a clear change in mass, but where's the impulse? Ok, so there might be an impulse in the y direction, but how about the x? Momentum's a scalar quantity, isn't it?

>> No.4849239

>>4849197
I'm pretty sure those bonds have some velocity in the direction the plane is going.

I didnt say it would retain its mass. The whole system (both pieces) retains its momentum. If half the mass falls off vertically then for momentum to be conserved in the x direction the velocity of the mass going in the x direction has to have doubled. So where did the force for that come from? Like I said the other piece wouldn't have fallen vertically naturally so there had to be a -x force on it right when it fell and the reaction force would be on the mass going in the x direction.

>> No.4849241

>>4849236
>Momentum's a scalar quantity, isn't it?

Nope.

>> No.4849247

>>4849241
I meant vector. Sorry. I live in Australia and it's late. There must be an impulse in the x direction.

>> No.4849248

>>4849164
Let's say there's a train moving at constant velocity, and there's a train-car filled with sand with a hole at the bottom. The sand leaks out over time, reducing the mass of the train and therefore its momentum. The train remains at constant velocity because no force has been applied to it It appears you changed momentum without applying a force, but this is because you haven't considered the whole system: the sand (which is still part of the system even after it leaks out) is initially traveling at the same speed as the train when it falls out of the hole, but it eventually transfers its momentum into the ground. So there WAS a force applied to the system as a whole by the ground. Psychologically most people don't consider the sand to be part of the system, hence the confusion.

>>4849205
Yes, it would have. Did you forget that p=mv?

>> No.4849249

It will make another straight but but inclined an angle relative to the original striaght line. The impulse is simply the change of momentum measured in the y-axis, whats the problem?

>> No.4849252
File: 24 KB, 445x456, tumblr_ksczlyQbeU1qzx4k0o1_500.jpg [View same] [iqdb] [saucenao] [google]
4849252

>>4849241
CARL!
YOU AGREED WITH ME ON SOMETHING!

Bro-fist?

>> No.4849254

>>4849248
see
>>4849216

>> No.4849262

>>4849252
lol, I just realized I don't have a brofist picture in my folder.

>> No.4849264

>>4849254
Please tell me you're trolling.

>> No.4849276

>>4849264

He is, its the new village idiot

>> No.4849277

>>4849248
Makes a little bit more sense now.

>> No.4849303

>>4849239
retain its velocity*

>> No.4849315 [DELETED] 

>>4849248

>The sand leaks out over time, reducing the mass of the train and therefore its momentum. The train remains at constant velocity

But the train wouldnt remain at constant velocity, think of a rocket moving in vaccum while ejecting propellor, it accelerates

>> No.4849361

>>4849315
AH!!!!!!!!!!!!

THAT MAKES SENSE! THERE'S MY ANSWER! IT MAKES PERFECT SENSE NOW!! I FORGOT THE 3RD LAW!! THANKS!

>> No.4849366

>>4849361
Ok, for some reason, the post was deleted. but anyway, the post said something about how rockets accelerate shitting gas out because of the 3rd law. This applies as well to my question.

Finally! I can sleep in peace