just throwin this out there

[americanjebus]

ok im just gonna throw this out there and maybe someone can chime in.

if i put in wrong section wich i think i did move this

but

Can the instantaneous acceleration of a body be non-zero at the same moment that the instantaneous velocity of the body is zero? If yes, explain.

its late and my brain is tired.

 

[Idealsupra]

IMO no...velocity is relative to acceleration...if there is zero velocity there must in turn be zero acceleration..and vice versa...

and yes wrong spot but ill move it

instantaneous movement

 

[americanjebus]

thx. after like 4 hours of homework and taking breaks to read sm. my brain is shot, especially while trying to comprehend teh whole maftpro thread and this acceleration/kinematics stuff ontop of tax return rules simultaneously.

 

[SupraMario]

No that would tear u to shreads,
that would mean your body which is at zero velocity, instantly accelerates, to above non -zero velocity.

 

[suprabad]

The answer is no. Just as two bodies cannot occupy the same space at the same time so it is to follow that one body cannot occupy two spaces at the same time. Get it? Simple Huh? :biglaugh:

 

[lanky189]

velocity is a change in accell and vector
accell is a change in speed. decrease or not.

maybe?

 

[GrimJack]

Definitely yes. We're talking instantaneous here, folks.

Imagine that you are flying along in outer space in your personal rocket ship. You turn the ship 180 degrees, so that your thrust will be exactly counter to your vector, and burn the rocket until you are going the opposite direction.

Now imagine the point where you have stopped completely - that instant where you have killed all your forward velocity and haven't quite gained any velocity in the opposite direction yet.

At that precise instant, you have zero velocity, however, your acceleration is still positive. Deceleration, to be precise, but physics doesn't really care that much about accel / decel.

 

[Squid699]

but techincally it IS accelleration, just accelleration on a new vector, completely opposite the former vector

 

[SupraMario]

grim, its impossible, think of it this way, ur body cant be at zero when you are moving.

 

[GrimJack]

Dead, that's not the question. The question is, can you be accelerating while at a stop?

Acceleration is a change in velocity. So if I go from 100mph to -100mph (going the opposite way) then for one instant, right in the middle, I am at a dead stop, even though my acceleration has remained constant through the entire sequence.

 

[IJ.]

Interesting debate guys !

 

[Idealsupra]

I dont know what all these big words mean so ill just sit here smile and nod

:biglaugh:

 

[IJ.]

ROFLMAO CRACKING UP here Jay!

 

[SupraMario]

Dead, that's not the question. The question is, can you be accelerating while at a stop?

Acceleration is a change in velocity. So if I go from 100mph to -100mph (going the opposite way) then for one instant, right in the middle, I am at a dead stop, even though my acceleration has remained constant through the entire sequence.

yea but ur acceleration is not constant because u have come to a stop. see what im saying you have to be a 0 somewhere, u cant go from 100 to 100, with out stopping and being at 0 somewhere. your body wouldnt be able to handle the rapid acc. and dec. to go from 100 to 0 to 100 INSTANTANIUSLY.
thats what i think, just my .02

 

[GrimJack]

Errr... I think I am doing a bad job of explaining something.

I'll use the car example, because it's familiar, despite the fact that it's a bad example. Just forget about traction, gears, brakes, etc. Forget about what your body can handle as well, we could just as easily be talking about an asteroid, a bullet, or a grain of sand - what the chunk of mass that you are dealing with is capable of withstanding doesn't apply.

So, take your car that is traveling 100mph in reverse, pop it into gear and apply acceleration forward. It doesn't have to be instant, just a gentle accel will do - even if it takes you an hour to go from -100mph to +100mph.

At the instant that you are at 0mph - freeze that snapshot. Your velocity at that point is zero. Your acceleration is still 200 mph^2 - you haven't let off the accelerator just because you came to a stop, as you can attest by trying this out in your car - though please use speeds MUCH slower than 100mph. You also need to ignore the fact that a car would usually decel using the brakes and then accel using the engine - which is why a car is a bad example.

Rocket engines are a better example - they get used in space, where there is little to no friction to worry about, and they can only provide positive thrust - no brakes in space.

 

[Tigerkat229]

Dead, that's not the question. The question is, can you be accelerating while at a stop?

Acceleration is a change in velocity. So if I go from 100mph to -100mph (going the opposite way) then for one instant, right in the middle, I am at a dead stop, even though my acceleration has remained constant through the entire sequence.

No....

If your at a dead stop then you have no acceleration. You had it until you stopped but at the point when you stop your instantaneous is still zero.

You can have velocity with no acceleration (driving at constant speed) but just look at the formula...

Instantaneous Accerlation = Limit (as the change in time approaches zero) of the Change in velocity / Change in Time

Or...look at the units of acceleration... m/s^2 (meters per second squared)...how do you have an accelration if your not moving per unit time?

 

[Tigerkat229]

Errr... I think I am doing a bad job of explaining something.

I'll use the car example, because it's familiar, despite the fact that it's a bad example. Just forget about traction, gears, brakes, etc. Forget about what your body can handle as well, we could just as easily be talking about an asteroid, a bullet, or a grain of sand - what the chunk of mass that you are dealing with is capable of withstanding doesn't apply.

So, take your car that is traveling 100mph in reverse, pop it into gear and apply acceleration forward. It doesn't have to be instant, just a gentle accel will do - even if it takes you an hour to go from -100mph to +100mph.

At the instant that you are at 0mph - freeze that snapshot. Your velocity at that point is zero. Your acceleration is still 200 mph^2 - you haven't let off the accelerator just because you came to a stop, as you can attest by trying this out in your car - though please use speeds MUCH slower than 100mph. You also need to ignore the fact that a car would usually decel using the brakes and then accel using the engine - which is why a car is a bad example.

Rocket engines are a better example - they get used in space, where there is little to no friction to worry about, and they can only provide positive thrust - no brakes in space.

I dont know what the purpose of this question was at the time he asked, but if it wasnt for NASA then space is not usually an element you have to consider in Physics classes (just like you can usually remove friction, wind resistance, etc).

As for your car example, if you EVER hit zero velocity...burning tires does not give you acceleration...a burnout, has zero velocity and zero acceleration...and since the question asked for the point at which velocity is zero...there is no acceleration there. Yes, you can accelerate and decelerate all you want and change velocities, but once you hit zero...your acceleration stops.

In space...yes...theres little restrictions so you will continue to move..

 

[americanjebus]

omg guys thnx for the help with my phys. homework but i already turned it in like 6 horus ago.

anyway i now realize i was probably wrong in putting no.

i made better sense of this by thinking of it as a dyno sheet.

rpms go up from zero to like 6000rpms and then go down right well between the last 1rpm and the zero rpm the engine is decelerating at say 1rpm per second for that single instant of measureable rpms the engine reaches zero on the last interval of decelerating at 1rpm per second.


thnx for the help on my physics homework but i didnt think i would stir stuff up like this. although it REALLY HELPS to comprehend what im learning when i apply it to my car. everything we have covered so far i have applied to something related to ars in order to comprehend it.

my final lab presentation is going to be behind the physics and forces involved in a turbocharge. gonna take a yard sale turbo, hook the turbine side to air compressor, and put a pressrue guage on compressor side for my demonstration, look forward for me to ask you guys for help on that too.

 

[SupraMario]

but im still confused grim what you are saying is that from -100 to +100 you are accelerating when ur body is at 0
but if you body is at 0 then isnt the car, hence you will be at a 0 velocity and not at a non-zero acceleration.

 

[lanky189]

:oops instantaneously::