Why Does a Passenger Continue Moving Forward When a Car Stops Suddenly?

[quark001]

Homework Statement

A passenger in a moving car is thrown forward when the car stops suddenly. Explain why this happens with reference to Newton's First Law.

Homework Equations

The Attempt at a Solution

"An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force." That explains why the passenger stops moving, but how does it explain why passenger stops moving only some time after the car stops moving?

 

[Ruddie]

Well, what about first checking out what the law actually is?

"Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it."

And, as some additional advice -the car is in fact 'pushing' the passenger.. And will stop pushing him when the car stops..
And what stops an object in the air..

I think that should be enough to help you!
And if you really can't figure it out yet - just tell me and I will give you another hint.. (but only if you really thought about it first..)

 

[Ruddie]

Abhishekdas - you are aware that you are not supposed to simply give him the answer, right? Check out the sticky at the top.

 

[Abhishekdas]

Ya...but i thought this was a conceptua question so...neway i will delete it...I do feel guilty...

 

[Ruddie]

Don't worry that much, just thought I would remind you of it - Please don't feel guilty :P

 

[quark001]

The car stops - so there is no unbalanced force acting on the passenger - which is why the passenger also eventually stops. I get that, but what I'm wondering is: why doesn't the passenger stop at the exact moment that the car stops?

 

[Abhishekdas]

The car stops - so there is no unbalanced force acting on the passenger - which is why the passenger also eventually stops. I get that, but what I'm wondering is: why doesn't the passenger stop at the exact moment that the car stops?

You are not getting your thinking right...Why should the car stop if there is no unbalanced force acting on it...It should remain in motion...According to Newton's First...Think...clearly...

 

[quark001]

Ok! :) The passenger should continue moving at a constant velocity until it hits the dashboard/seatbelt, which provides the unbalanced force for it to stop.

Why doesn't this happen to the passenger when the car stops really slowly?

 

[Ruddie]

Simple:
- You will try to push yourself back presumably
- Your seatbelt also pushes you back a little
- Air resistance

So - It does, you just don't notice it that much.

 

[Abhishekdas]

Another reason why you can't experience it when it stops slowly maybe that the static friction limit is not exceeded if we decellerate slowly...

 

[quark001]

Thanks, that makes sense. I guess it was a stupid question from the start :)

 

[Abhishekdas]

No...it was not stupid...The transition from younger classes to core physics is not so easy...Yow know what...?

When i first got to know that... if you apply a force and give a body some velocity and you leave it in a space where there is no force acting it will keep going for ages...i just could not believe it...i really got the shock of my life...i was like how can a body move if there is no force on it...i could not digest it...Actually we live in world so far from the ideal situations which we oven have to face while studying ...it at times does take time to grasp these things...

And that's why we should realize how intelligent and great people like Newton and the other scientists were...To actually realize these things...