Is there such a thing as instantly stopping?

Question

I'm sorry if this is a stupid question, but I've never taken a physics class and I was curious about something. But anyway, my question is, is there such a thing as instantly stopping? For example, if I'm traveling at 70MPH and I hit a wall, between the time that I am going at full speed and when I hit the wall, do I slow down until I reach zero, or do I instantly stop? Do I go every speed in between 70 and 0?

I'm sorry if my question is unclear. If it is, please leave a comment and I'll try explaining it more.

score 4 · Accepted Answer · answered Feb 14 '14 at 00:38

4

To stop instantly, you would need infinite deceleration. This in turn, requires infinite force, as demonstrable with this equation: $$\vec F=m\vec a$$ So when you hit a wall, you do not instantly stop (e.g. the trunk of the car will still move because the car is getting crushed). In a case of a change in momentum, $m\vec v$, we can use the following equation to calculate force: $$F=\frac{\Delta{p}}{\Delta{t}}$$ However, because the force is nowhere close to infinity, time will never tend to zero either, which means that you cannot come to an instantaneous stop.

answered Feb 14 '14 at 00:38

Ruben

663

I can't upvote it, but I marked it as an answer. Thank you. – Michael Blake Feb 14 '14 at 00:45
Could you mention why an infinite force is unreasonable? – BMS Feb 14 '14 at 06:50

Is there such a thing as instantly stopping?

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