I Why things do not stop immediately?

  • Thread starter parshyaa
  • Start date
303
19
Why things do not stops immediately when a retarding force is applied on a moving ball.
  • I know this is a foolish question but I have tried to give the answer
  • my attempt : suppose I have applied force on a moving ball(its moving on a non frictional plane) and I want to stop it immediately means at a time = 0.
  • F = m.a(this is a retarding force applied on ball and 'a' is the constant deaccelaration due to force on a ball )
  • a = dv/dt , adt = dv , suppose initial velocity of a ball is 0.
  • ∫a dt = ∫dv , lower limit and uppar limit for velocity is 0 and v and for time 0 and t
  • Therefore v = at , to get immediate stop, t =0 , in that case a = ∞ , and F = ma , ∴F = ∞ , but it is impossible to apply infinite force. Therefore it is impossible to stop things immediately.
  • What's your answer or opinion
 

andrewkirk

Science Advisor
Homework Helper
Insights Author
Gold Member
3,717
1,344
Your reasoning looks correct. Average acceleration is change in velocity divided by time. So to change velocity by a nonzero amount in zero time would require infinite negative acceleration, which would require infinite force.

If you watch slow-motion footage of a cricketer or baseballer catching a fast ball, you'll see they let their hand(s) move backwards a little way after making contact. That increases the deceleration time, thereby reducing the force, thereby reducing the likelihood of the ball bouncing out of their hands (as well as lessening the potential damage to their hands).
 
303
19
Thanks andrewkirk for fielders example.
 

russ_watters

Mentor
18,405
4,653
Why bother with the math? You should be able to just state Newton's First Law of motion.
 
303
19
Why bother with the math? You should be able to just state Newton's First Law of motion.
Yes you are right but maths makes everything more clearer
 
303
19
If you say so....let me know if your teacher agrees.
Hee hee , what's wrong in this answer , this question was mine and I will not showiy to my teacher. ^_^ ^_^
 
3,722
405
  • a = dv/dt , adt = dv , suppose initial velocity of a ball is 0.
So you want to "stop" a ball with zero initial velocity?
You can do this instantaneously. :smile:
 
303
19
nasgot itpost: 5565525 said:
So you want to "stop" a ball with zero initial velocity?
You can do this instantaneously. :smile:
Hey nasu u got it , I was thinking of editing , ball was moving with constant velocity v and limit should be from v to 0 . And equation will be at = -v , a = -(v/t) it is negative because retarding force was applied ,
 

Want to reply to this thread?

"Why things do not stop immediately?" You must log in or register to reply here.

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving

Hot Threads

Top