Why do balloons behave differently from cars when braking?

[smartboy]

my question is about the Newton's laws:

1. if a car suddenly brakes all the objects in the car tends to move forward by a force but a balloon tends to move backward, why?

2. if we tie two strings in two sides of a weight and hang the weight by one string and slowly pull the other string slowly the top string breaks apart and the weight falls down (because both the weight and the pull acted on the top string) but if we pull the string fast the string breaks apart before the weight and the weight doesn't fall down, why?

3.how can i find the acceleration for a roller caoster from a distance time graph (actual acceleration) and from the height and lenth (ideal acceleration) of a ramp?

 

[andrevdh]

1. It might be due to the air being slightly compressed at the front of the car against the windscreen since the air also moves forward. This compression wave is then propagated towards the rear of the car, pushing the balloon backwards. The wave amplitude will quickly die out though and will have virtually no effect on it's return path. The same effect is found when a boxer is hit against his head - his brain is pushed by the liquid in his head in the same direction as that of the applied force thereby hitting the opposite side of the head - not as one would think the same side as where the punch was applied!

 

[CarlB]

Where the balloon goes depends on what's in it. If there's air, it won't move much. If it's helium then it will go to the back of the car because helium is lighter than air (and air goes to the front).

Carl

 

[andrevdh]

One can build an amusing device that displays the same principle. Put an horizontally spinning structure in a glass bowl. Stick a burning candle on the edge of disc and spin it. Guess in which direction the flame will point?

 

[Tide]

1. An air filled balloon suspended from the ceiling will, in fact, move forward.