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DPJ said:
No, you don't understand this!

Acceleration can change from 10m/s/s instantaneously to 0m/s/s if the force is removed instantaneously.

Acceleration is the rate of change of velocity. If velocity suddenly stops increasing, acceleration ceases.

Please come back with a proven arguement rather than unproven theories.
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haha, ok, i think i get this now, i was incorrect in my thoughts of acceleration and i fully admit this.

however.....

F = ma
Net force = mass x acceleration

mass cannot change so when net force is 0 acceleration must also be zero.

heres the kicker, show me a car that can instantaneously remove driving force!

As the clutch is in the process of disengaging the gear box, there will still be some aero dynamic drag applying a driving force although, this will decrease as the clutch is depressed. the driving force will be removed once the clutch if fully engaged!
 
Although the force accelerating the car is removed instantaneously by depressing the clutch (it isn't really instantaneous but we can assume so for the sake of this discussion) the car still has momentum and at the point the power was removed that momentum was increasing (momentum = mass x velocity). My argument is that when a car is accelearting as quickly as we are talking about (around 7 seconds to 60 mph) its momentum will be increasing at such a rate that the forces trying to stop the car moving (drag, friction etc etc) will not be high enough to halt that acceleration instantaneously, it will take a very small amount of time before those forces have reduced the acceleration to zero and actually turned it into deceleration, it will be a very small amount of time as I have already said and the object will never increase or even maintain its rate of acceleration and will ultimately stop. If something is heavy enough and accelerated really quickly I don't think that aerodynamic drag and mechanical resistance will always be enough force to halt the rate of acceleration to zero instantaneously. Whether our cars have enough mass and acceleration for this to be the case is hard for me to prove without lots of calculations and reliable data but its what I believe to be the case.

Matthew.
 
The other thing is that although force = mass x acceleration, the power generated by the engine is not the only force exerted on the car, there are all the others, just because you reduce the force from the engine to zero, force in this equation will not be zero, as the mass isn't zero then neither is the acceleration. The only time that the acceleration will be zero is when the sum of all forces acting on the car are equal resulting in no change in velocity to the car, ie constant speed caused by the power from the engine and the momentum of the car being equal to all the drag and mechanical resistance suffered by the car.
 
matt-drummer said:
The other thing is that although force = mass x acceleration, the power generated by the engine is not the only force exerted on the car, there are all the others, just because you reduce the force from the engine to zero, force in this equation will not be zero.
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actually it will be less than zero, force is net force i.e. all the forces added to together including the negative ones (wind resistance, mechanical drag etc.) since the negative forces will be greater than the force of moomentum alone the force in this equation will be negative making acceleration negative.

also, how the f**k did we get started on this???? i cant even remember now!
 
As my final say on this.....

I dont see threads like this as an argument (as some people seem to see it). I have learnt from partaking in this thread and that is is exactly why I am a member of this forum, I enjoy taking part in constructive debate!

If people think I am arguing for the sake of it, please dont. I am simply putting forward my view of things in the hope of gaining a better understanding by reading the replies of my fellow members.

Peace out! :)
 
You're all now making this far too complex.

The issue is about whether a car keeps accelerating after the clutch is depressed. The moment before the clutch is depressed, you've lifted off the throttle. You need only to look at Vag-Com logs to see that at that point, the load is removed from the engine (ie Force removed). No more acceleration at that point.

I can drive my car in say sixth gear and accelerate hard, then gradually reduce my rate of acceleration to 0. Or, I can accelerate hard in sixth and suddenly lift off. Instant change of acceleration to zero.

It is possible to change a high rate of acceleration to a high rate of deceleration instantaneously. Consider a falling lead weight. It's accelerating at 9.8 m/s/s. Let's say that 0.0001mm before it hits the ground, it's moving at 30m/s. The moment it hits the ground, it's doing 0mph. The weight has instantly gone from accelerating at 9.8m/s/s to decelerating at 30m/s/s (with ever showing another acceleration rate.
 
haha, you might be right but just imagine how much quicker newton would have come up with his laws if he had scn to post his ideas on!!! :)
 
skahigh said:
haha, you might be right but just imagine how much quicker newton would have come up with his laws if he had scn to post his ideas on!!! :)
Click to expand...

If he'd come round to my house, I'd have been dropping MAFs on his head instead of apples! :D

Interestingly, you make a good point. Newton & Co got their 'momentum' to advance ideas more rapidly from being in regular contact/competition with like minds. :cartman:
 
You all sicken me with talk of the laws of physics.

Cars work by magic alone. Stop this blasphemy now!
 
and perhaps we should at long last put this thread to bed only to be resurrected in a few months when someone else asks the question! :)
 
what affect would weight transfer have on a car? i.e. you accelerate the weight goes to the back of the car you put the clutch down and the weight goes back to the front of the car (bit like lift off over steer)

I'm sure I've noticed a similar thing with braking but I could be going mad, lol, say you brake from 60 - 0 (car in neutral or clutch down) and just before you come to a complete stop you come off the brakes and car seems to surge slightly, anyone experienced this?

its like if you spin a raw egg you can stop it spinning briefly with your hand, take your hand off and it'll start to spin slightly
 
WE SEEM TO HAVE GONE FROM 0-60 TO 60-0!!!!
it doesnt matter bout weight shift coz the weight is increased to the rear when it shifts from the front and vice versa.still the same resistance!!!dont know why ive got involved in this again!!!!!!
 
jonathanp said:
I'm sure I've noticed a similar thing with braking but I could be going mad, lol, say you brake from 60 - 0 (car in neutral or clutch down) and just before you come to a complete stop you come off the brakes and car seems to surge slightly, anyone experienced this?
Click to expand...

that is an odd feeling but it is because your body is so sensitive to environmental changes like acceleration (trust me im a psychologist). as you are braking negative acceleration is occurring, when you lift off, negative acceleration becomes less and your body detects this change making you feel like you are surging forward when actually you are just slowing down your rate of decelleration! :lol:

read THAT once!
 
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