I've been wondering what happens to acceleration when a car reaches the maximum velocity that is capable to produce (let's say 250 km/h). I would assume that the acceleration is decreasing until it reaches 0, but what exactly is decreasing the acceleration? Why can't the car accelerate even more? I know this question might be stupid but I'm really struggling.
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2 Answers
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The force generated by the engine to accelerate the car forwards remains more or less constant (ignoring the effect of changing RPM), but the faster the car gets the greater the forces decelerating it — air resistance and friction with the ground and within the drive train. When the car reaches its maximum speed, those opposing forces are in balance, which is why it can’t then go any faster.
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$\begingroup$ So, if we ignore the air resistance and friction there wouldn't be anything to stop the car from accelerating? $\endgroup$ Mar 6, 2023 at 23:24
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$\begingroup$ @Randomdude That’s correct, a car with no air resistance or friction could keep accelerating for ever, or at least until it left the ground and went into orbit, or ran out of fuel. $\endgroup$ Mar 6, 2023 at 23:26
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1$\begingroup$ You would need an infinite series of gear ratios. The RPM limit on the engine is fixed by internal stresses (e.g. linear acceleration of the pistons or centrifugal forces in the electric motor), and by airflow constraints through the induction, valves and exhaust. $\endgroup$ Mar 7, 2023 at 13:06
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1$\begingroup$ @MikeScott Or reached the speed of light. You'd need a pretty long straight track for that though. (And one that's truly straight, not on the surface of a spherical-ish planet.) $\endgroup$– GrahamMar 7, 2023 at 16:42
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When the car reaches the maximum acceleration it could possibly achieve, ignoring all other forces acting on it, it would have achieved a state known as 'terminal velocity', in accordance to Newton's first law, which essentially means that the car would travel at a constant velocity forward forever, as you can see in the graph attached, which shows the acceleration-time graph for a free fall situation- a skydiver's acceleration as he dives downwards; and it is quite clear that over time, as air drag cancels out gravitational pull on the skydiver, that the acceleration eventually goes to 0, and that is what it is meant to reach 'terminal velocity'. However, that is not realistic in real life as there are other factors slowing down the car when it reaches terminal velocity, such as friction, air drag ect.
![Free fall acceleration-time graph][1]
[![Free fall terminal velocity graph][1]][1]
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$\begingroup$ Terminal velocity of an object falling in atmosphere is caused by drag, that's not an "other factor". $\endgroup$– BarmarMar 7, 2023 at 16:50