Answer to Question #63382 in Physics for Maria

Question

1. If you release a balloon in air in this condition which law can apply according newtons law of motion and why?

Answer 1

Newtons's first law states:
An object at rest will remain at rest unless acted on by an unbalanced force. An object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

If the balloon is filled with helium, its weight is less than the upthrust force produced by air. Thus, the upthrust force is not balanced by weight, and the balloon accelerates upwards.
If the balloon is flled with air, its weight is greater than the upthrust force produced by air. Thus, the weight is not balanced by the upthrust force, and the balloon accelerates downwards.