A helium balloon hovers in midair, neither ascending or descending, is it in equilibrium? What forces act onit?
The balloon is static in mid air. So it is in equilibrium. The gravity force tries to pull it down. The bouyant force acts vertically upwards. The two forces acts through the center of gravity of the balloon in same line but opposite direction and cancels each other. So it is in equilibrium. Remember if gravity force is greater it will come down with acceleration. And if bouyant force is greater it will go up with acceleration. Hope it helped.
