Acceleration Physics

[kambites]

yorkshireegg said:

kambites said:

If they hit the throttle at the same time they stay the same distance apart.

If they hit the throttle at the same point on the road, the gap between them extends.

OP said:

they both hit the throttle at the same time

Indeed, so in that case the gap stays the same.

[mrmr96]

joewilliams said:

kambites said:

If they hit the throttle at the same time they stay the same distance apart.

If they hit the throttle at the same point on the road, the gap between them extends.

Giving the original author the benefit of the doubt, this is probably what is meant.

Indeed, but it's not what he said. He said "at the same time" not "upon crossing the same mark on the road".

[richwig83]

TATOR said:

I think the car behind would shorten the gap due to drafting off the one in front (but i really dont have a clue

That is what I would have thought too. Slipstream effect reducing drag on the rear car enabling faster acceleration.

[thehammer]

james_gt3rs said:

Presumably the opposite would happen! The slipstreaming effect would make the car behind accelerate faster and go into the back of the car infront.

it would happen in the real world but it states that they have identical acceleration characteristics so this doesn't apply here.

[RobM77]

mrmr96 said:

joewilliams said:

kambites said:

If they hit the throttle at the same time they stay the same distance apart.

If they hit the throttle at the same point on the road, the gap between them extends.

Giving the original author the benefit of the doubt, this is probably what is meant.

Indeed, but it's not what he said. He said "at the same time" not "upon crossing the same mark on the road".

Yes, Kambites just mentioned it to suggest where the confusion probably arose from.

[GadgeS3C]

marshalla said:

OK - let's do it properly, "two perfectly spherical vehicles, in a vacuum, and subject to no gravitational, frictional or other forces except those provided by their own propulsion systems...."

Must...resist...asking...how...they...can...then...accelerate?

Sorry

[marshalla]

GadgeS3C said:

marshalla said:

OK - let's do it properly, "two perfectly spherical vehicles, in a vacuum, and subject to no gravitational, frictional or other forces except those provided by their own propulsion systems...."

Must...resist...asking...how...they...can...then...accelerate?

Sorry

Read
The
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Properly

[NISaxoVTR]

marshalla said:

GadgeS3C said:

marshalla said:

OK - let's do it properly, "two perfectly spherical vehicles, in a vacuum, and subject to no gravitational, frictional or other forces except those provided by their own propulsion systems...."

Must...resist...asking...how...they...can...then...accelerate?

Sorry

Read
The
Question
Properly

Nothing would ever move in this proposed test universe so nobody would have asked this question, or exist .

[RobM77]

NISaxoVTR said:

marshalla said:

GadgeS3C said:

marshalla said:

OK - let's do it properly, "two perfectly spherical vehicles, in a vacuum, and subject to no gravitational, frictional or other forces except those provided by their own propulsion systems...."

Must...resist...asking...how...they...can...then...accelerate?

Sorry

Read
The
Question
Properly

Nothing would ever move in this proposed test universe so nobody would have asked this question, or exist .

Newton's third law? If one sphere pushes out a mass (e.g. from a propulsion system) then it'll move in the opposite direction.

[marshalla]

RobM77 said:

ewton's third law? If one sphere pushes out a mass (e.g. from a propulsion system) then it'll move in the opposite direction.

Someone'll be along in a minute to say that it won't work because there's nothing for it to push against...

[RobM77]

marshalla said:

RobM77 said:

ewton's third law? If one sphere pushes out a mass (e.g. from a propulsion system) then it'll move in the opposite direction.

Someone'll be along in a minute to say that it won't work because there's nothing for it to push against...

I'd ask them to watch a spacecraft manoeuvring!

[J4CKO]

What if they are on a conveyor belt ?

[57Ford]

Full bore acceleration at a distance of 20 feet. These are Audi A4 TDi/ BMW 320d's we're talking about, yes?

Sorry, couldn't resist

As others have said, the website is flawed and the gap would remain constant or indeed close up due to the slipstreaming effect.

[Mr2Mike]

57Ford said:

As others have said, the website is flawed and the gap would remain constant or indeed close up due to the slipstreaming effect.

The OP specified that both vehicles have identical acceleration. If drafting caused the gap to close, this would no longer be true.

[NISaxoVTR]

RobM77 said:

Newton's third law? If one sphere pushes out a mass (e.g. from a propulsion system) then it'll move in the opposite direction.

Which is in affect with a car tyre on the road, but without friction there would be no force exerted and the cars wouldn't move .

[Super Slo Mo]

NISaxoVTR said:

RobM77 said:

Newton's third law? If one sphere pushes out a mass (e.g. from a propulsion system) then it'll move in the opposite direction.

Which is in affect with a car tyre on the road, but without friction there would be no force exerted and the cars wouldn't move .

But if you have something that allows you to fire particles with mass out of the back of the car, gas for example, then you have propulsion. You don't need friction.

[Mave]

NISaxoVTR said:

Which is in affect with a car tyre on the road, but without friction there would be no force exerted and the cars wouldn't move .

Rockets don't have car tyres, and they manage to move :-)

[57Ford]

Mr2Mike said:

57Ford said:

As others have said, the website is flawed and the gap would remain constant or indeed close up due to the slipstreaming effect.

The OP specified that both vehicles have identical acceleration. If drafting caused the gap to close, this would no longer be true.

I simply took it to mean identical vehicles. Guess you're talking about identical acceleration characteristics within this particular scenario. Yes, in that case you're right. But the other forum's still wrong.
Yay for PH!

[anonymous-user]

Only if they accelerated to beyond the speed of light, would the distance between them change. So they would have to be either the Starship Enterprise or a 335d..........

[RobM77]

NISaxoVTR said:

RobM77 said:

Newton's third law? If one sphere pushes out a mass (e.g. from a propulsion system) then it'll move in the opposite direction.

Which is in affect with a car tyre on the road, but without friction there would be no force exerted and the cars wouldn't move .

Newton's third law does not require friction to work. A car tyre moves a car forwards because it rotates and there's friction between the tyre and the road; the tyre is circular, so whilst it's pushing on the road, it's not actually going anywhere. However, if you fired cannon balls (or car tyres!) out of the back of a car then the car would move forward, even if it was in a vacuum or there was no friction on the road (in fact it'd move faster without friction!) - that's the essence of Newton's Third Law.