Acceleration and velocity

[cyruseternity]

Why cant acceleration and velocity cannot change abrubtly at an instant..??

[Robittybob1]

Why cant acceleration and velocity cannot change abrubtly at an instant..??

Where is the energy going to come from? I drove out in front of a thousand tonne train doing 100 km/hr and my car changed acceleration and velocity "abruptly". Define abruptly? Do you mean instantly? Or even "in no time at all"?

[cyruseternity]

Yes i do mean in no time at all

[Janus]

An instantaneous change of velocity means an infinite acceleration.

 

Acceleration is equal to force/mass, so for any object with a non-zero mass, it would take an infinite force to cause the infinite acceleration needed for an instantaneous change of velocity.

 

As for a change in acceleration,(sometimes called "jerk") there is nothing that expressly forbids an instantaneous change in acceleration, but real world conditions tend to smooth it out to being non-instantaneous.

[Robittybob1]

An instantaneous change of velocity means an infinite acceleration.

 

Acceleration is equal to force/mass, so for any object with a non-zero mass, it would take an infinite force to cause the infinite acceleration needed for an instantaneous change of velocity.

 

As for a change in acceleration,(sometimes called "jerk") there is nothing that expressly forbids an instantaneous change in acceleration, but real world conditions tend to smooth it out to being non-instantaneous.

When a high energy ray interacts with a molecule would that be a instantaneous change? (as in a shock-wave initiating a nebula collapse.)

[studiot]

 

When a high energy ray interacts with a molecule would that be a instantaneous change? (as in a shock-wave initiating a nebula collapse.)

 

 

The uncertainty principle ensure that changes of magnitude take a finite time to occur for massive particles (particles with mass)

 

Special Relativity ensures that particles without mass (photons) cannot change velocity magnitude.

 

But sure both acceleration and magnitude are vectors so can instantaneously change direction when going in curvilinear motion.

Edited November 6, 2014 by studiot

[Robittybob1]

 

The uncertainty principle ensure that changes of magnitude take a finite time to occur for massive particles (particles with mass)

 

Special Relativity ensures that particles without mass (photons) cannot change velocity magnitude.

 

But sure both acceleration and magnitude are vectors so can instantaneously change direction when going in curvilinear motion.

Was that last sentence the answer to my question? ( I was wanting to know if a photon or other radiation that when moving at/near the speed of light can interact with a particle that must in all intents be stationary (moving slowly) as implied in the concept of shock-wave.)

A photon has momentum and can that momentum be transferred in an interaction? Would that interaction be instantaneous?

I didn't know what the last sentence means, but it does it have something to do with the definition of Pi, a number which never comes to an end, so the transition in curvilinear motion is impossible to define too isn't it? The curve (at the limit) is so gentle that it too probably can't be called instantaneous either.

Edited November 6, 2014 by Robittybob1

[Strange]

 

I didn't know what last sentence means but it does it have something to do with the definition of Pi

 

How do you get to that conclusion? The sentence said nothing about angles, circles, circumferences or diameters...

 

a number which never comes to an end

 

I don't know what it would mean for a "number to come to an end". Perhaps you mean, "the numerical expansion of which can never be written down." The exact value of Pi can, of course, be written down in a few symbols. But why that would be relevant to the question, I don't know.

 

, so the transition in curvilinear motion is impossible to define too isn't it? The curve is so gentle that it too probably can't be called instantaneous either.

 

I believe the point being made was that the velocity and acceleration in this case are continuously changing. You can therefore, in the limit, view this as a continuous sequence of (infinitesimally small) instant changes. Basic schoolboy calculus.

[studiot]

Sorry to have caused the confusion, I have editied my previous post to what I should have written.

 

Rectilinear = in a straight line

 

Curvilinear = in a curving line

 

The linear part = line and the prefix tells whether the line is straight or not.

 

As to the abrupt part I suppose a rolling irregular object could have corners that follow a cuspate path and thus suffer abrupt changes of direction.

[Robittybob1]

 

How do you get to that conclusion? The sentence said nothing about angles, circles, circumferences or diameters...

 

 

I don't know what it would mean for a "number to come to an end". Perhaps you mean, "the numerical expansion of which can never be written down." The exact value of Pi can, of course, be written down in a few symbols. But why that would be relevant to the question, I don't know.

 

 

I believe the point being made was that the velocity and acceleration in this case are continuously changing. You can therefore, in the limit, view this as a continuous sequence of (infinitesimally small) instant changes. Basic schoolboy calculus.

OK I was a bit lost but you sort of recovered it thanks. I was thinking of curves, especially something moving in a circle, I was thinking you can't say it changes instantaneously.

Forgive me if I'm a bit confused regarding what was meant by curvilinear motion.

Any motion when looked at the limit might be in the form of "infinitesimally small instant changes". Was there a difference if the motion was rectilinear or curvilinear?

Edited November 7, 2014 by Robittybob1