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Physics

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    $\begingroup$ Acceleration is "the rate of change of velocity per unit of time" . It is not a force-applying [mechanism]. +1 $\endgroup$
    – Mazura
    Commented Dec 5, 2018 at 2:24
  • 54
    $\begingroup$ Thanks for the mental image of a car slamming into a giant spring. $\endgroup$
    – sampathsris
    Commented Dec 5, 2018 at 7:12
  • 10
    $\begingroup$ This is how a spacecraft slows down. It rotates so that its rocket nozzle is pointing in the direction of motion. Then it fires the rocket to produce a force and decelerate. If it kept the motor burning, it would eventually stop and then accelerate back the way it came. $\endgroup$
    – Oscar Bravo
    Commented Dec 5, 2018 at 15:25
  • 42
    $\begingroup$ Essentially: braking (friction) is a multiplicative. No amount of multiplying by 0.9 will ever make a positive number negative. Rockets, on the other hand, are additive (and you can absolutely add a negative number to a positive one and end up with a negative number). $\endgroup$
    – Draco18s no longer trusts SE
    Commented Dec 5, 2018 at 21:56
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    $\begingroup$ @Draco18s An interesting simplification, although if true it would mean you can't stop your car with the brakes (no amount of multiplying by 0.9 will ever make a positive number zero either)! $\endgroup$
    – Dan Staley
    Commented Dec 6, 2018 at 19:54