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/sci/ - Science & Math

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1845123 No.1845123 [Reply] [Original]

Ok guys, my mind is full of fuck.

The question is, is there acceleration with 0 velocity? Before you jump to conclusions, hear me out.

If you throw a ball in the air, it goes up and comes down and is constantly in some state of acceleration, even though at the very peak velocity was 0. So, this would suggest that acceleration is possible without velocity.

However, a=Δv/Δt, and if Δv=0, a = 0, correct?

Anyways, I have some physics assignment where I am to describe an object with positive displacement, zero velocity, and positive acceleration. My current answer is "not possible", where am I going wrong? Or, am I right? WTF

>> No.1845130

>>1845123
You cannot have acceleration without velocity. At the peak of the objects parabola, it had 0 velocity and therefor 0 acceleration.

>> No.1845129

Jesus christ, you just described one.

>> No.1845134

>The question is, is there acceleration with 0 velocity?
yes

>and if Δv=0, a = 0, correct?
no because at the peak v=o but the delta v isnt 0.

>> No.1845137

When velocity is nearing 0, acceleration is rapidly lowering. When velocity finally reaches 0, acceleration has stopped as well.

Impossible, I would think.

>> No.1845153

>>1845134

Yes, but the question is "IF it has no velocity, what does acceleration look like" not "Does it have velocity at the peak." My first example appears to be erroneous, which reinforces my view that acceleration cannot exist without velocity

>> No.1845169

>However, a=Δv/Δt, and if Δv=0, a = 0, correct?
Average velocity = Δx/Δt
Average acceleration = Δv/Δt
Instantaneous velocity = dx/dt
Instantaneous acceleration = dv/dt
Usually when you talk about velocity and acceleration, you talk about the instantaneous kind, which is the limit as Δt approaches zero. So you can have an instantaneous velocity of zero, and at the same time an instantaneous acceleration, which is when the ball is at the peak.

If you think about you can even have an average velocity of zero over a Δt when the ball is at the peak. It just requires that at the ball returns to the same place at the end of the Δt that it was at the beginning of the Δt.

>> No.1845186

>>1845153
>Yes, but the question is "IF it has no velocity, what does acceleration look like"
If it couldn't have acceleration without velocity, it could never achieve velocity. Acceleration is what gives something velocity, so obviously something can have acceleration without velocity.

>> No.1845191

Protip, all of you armchair physicists: if an object has 0 velocity AND 0 acceleration while following a parabolic trajectory, it's floating in the air. No movement.

Objects that don't have an applied force are always accelerating toward the Earth at a rate of 9.8m/s^2. If not Earth, than toward the closest massive body at whatever rate that may be. No exceptions.

>> No.1845198

My physics teacher said there were people who didn't understand this. I didn't believe him.

Sadly, I was proven wrong today.

>> No.1845209

>>1845130
>>1845137
this thread makes me cry

>> No.1845211

>However, a=Δv/Δt, and if Δv=0, a = 0, correct?

In that case, Δt = 0 too. HOLY SHIT BATMAN, LIMITS!

>> No.1845224

>>1845186

It would lie at rest until an outside force acted upon it. Acceleration and velocity are both dependent upon initial force, one is not causal of the other. A car isn't accelerating until velocity changes.

>> No.1845227

>>1845211

Δt = any real number. 0/arl = 0

>> No.1845240

...

I cannot believe the amount of idiocy in this thread. acceleration is the result of a force on a mass. If you throw a ball upward, the acceleration due to gravity acts on it all the way. It decreases the velocity upwards and increases it on the way down. No it doesn't become zero at the zenith of the trajectory. It REMAINS CONSTANT the whole way through, at about 9.8 m/s^-2 for the earth's surface. Acceleration is a rate of change in velocity. If velocity is changing, it doesn't matter if it's zero or over 9000. There's acceleration involved.

a = F/m

a = d(v)/d(t)

>> No.1845275

Wow, this is really pathetic.

> a=Δv/Δt
> Δv
> delta v

If there is no change in velocity there is no acceleration. It does not mean an object is not moving, it means the objects velocity remains unchanged. If a ball is dropped and reaches a velocity of 0 at the top of its trajectory, there will be a change in velocity, thus Δv DNE 0. Fuuuck.

>> No.1845303
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1845303

>>1845209
Indeed

OP, maybe this can help: Try to imagine the graphs of A, V, and Y when you throw the ball.

>> No.1845350

>>1845303
Shit, I just realized I forgot the m/s^2 on the graph of A.

acceleration is in meters/seconds^2
velocity is in meters/seconds
position is in meters

if you know calculus, think of meters as y and seconds as x
acceleration: dy/dx^2
velocity = dy/dx
position = y

Also, there is a difference between velocity over time and instantaneous velocity. Δv can only be zero when Δt is also zero. Δv/Δt becomes 0/0, so using that to evaluate what a is no longer becomes viable. If Δv is anything besides zero, Δv/Δt will always result in the constant value for acceleration.

>> No.1845393

>Δv can only be zero when Δt is also zero

wat?

if vf-vi is 100-100 then Δv is 0, regardless of the time. This is shown when it crosses the x-axis it your graph and t =/= 0.