Force and Motion Question (Physics)?

Question

Consider a child holding a helium balloon in a closed car at rest. What would the child observe in the car if a) accelerates from rest and b) breaks from a stop? (the ballon does not touch the roof of the car.)

Answer 1

Newtons third law of motion states that for every acting force there is an equal an opposing force.

At rest the balloon experiences no unbalanced forces but as the car accelerates it is exerting a force forwards therefore there is a backwards force exerted on the balloon so it should move backwards. (if you imagine yourself in a seat and this happening you find that you are pushed against the seat, this is because there is that equal opposing force acting on you just as on the balloon)

b) if a car breaks it is decelerating to a stop and so the car is exerting a force backwards, there fore a force will be exerted on the balloon to move forwards. (if you imagine this part happening again with you in a seat you find that you are pushed forward as the car breaks, this because of that equal force acting on you just as on the balloon)

=]

Answer 2

It's the opposite of what Maureen said.

When the car accelerates, the air in the car (and the balloon) all tries to stay stationary (until the back window pushes the air forward along with the car). So all this air is trying to congregate at the back. Being more dense than the balloon, the air pushes the balloon out of the way -- toward the front of the car. It's buoyancy tipped a bit sideways because the acceleration of the car is added to the acceleration due to gravity.

The opposite happens when the car brakes.