Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Inertia of a man driving a car

  1. Jan 1, 2005 #1
    a man was driving a car, with him was his friend inside the car along with a box full of godies, and a helium fill baloon.

    suddenly he stops the car.

    now you have to tell, what will be the effect of this breaking (negitive acceleration) on all the four bodies( both men, box of goodies and the helium filled baloon.)
  2. jcsd
  3. Jan 1, 2005 #2
    Gets a car , a friend , a box of goodies and a helium balloon. Puts them all in the car and drives. After sometime realises, that he cant drive. Desparately attempts to brake but no luck and crashes. So the effect of braking on me and my partner was that we were in the hospital , the box of goodies i learnt were taken as goodwil gift by the inspecting policeman and the balloon well i offerred it to the good looking nurse.

    -- AI
    But in your example,
    the two men move forward (inertia),
    the box of goodies , well i ate them
    and the helium balloon moves backward (inertia) .
  4. Jan 1, 2005 #3
    Newton’s first law would apply to all four bodies. However, the balloon would float towards the back of the car because the air around it will rush towards the front.
  5. Jan 4, 2005 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    I suspect your troubles resulted from trying to put a car inside a car. :wink:

    ::The helium balloon moves in the same direction as the center of mass of the air inside the box of goodies. ::
  6. Jan 4, 2005 #5
    The driver not wishing to consult Newton's first, and putting shades on all the car windows, discovers that according to GR use of the 'brake' has created a new gravity source directly in front. All the objects react to the additional gravitational force in front of them exactly as they have been reacting to the one still below them. Including the helium balloon that seems to be repelled from the ground below.
  7. Jan 6, 2005 #6
    Hehe, i never realised that! So were they really brakes i was trying to apply there :eek:

    -- AI
  8. Jan 6, 2005 #7


    User Avatar
    Science Advisor

    The helium balloon will tend towards the rear of the car during the braking. All of the the others will tend to the forward direction until restraining forces bring them to a stop.
  9. Jan 8, 2005 #8
    does this mean that i was the only one in this whole world who took a week to get to the answer to this question.

    obviously, everybody else seems to know the answer immidiately.
  10. Jan 12, 2005 #9
    today on my way to college, i saw a boy walking with a helium baloon in his hand.

    so what if i change the situation in this case. suppose a man is running or walking(in linear motion), while holding on to a long thread tied to a helium baloon. what will be the effect of his sudden acceleration or retardation on the baloon. will it still be the same as was in the case when the baloon was inside the car??
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook