Naima is standing on a hillside. She is holding a helium-filled balloon on a string. If she releases the string, what happens to the balloon and why?

Respond very briefly.
The helium-filled balloon will rise upwards once Naima releases the string. This is because helium is lighter than the surrounding air. The buoyant force, which is the upward force exerted by a fluid that opposes the weight of an object immersed in it, is greater for the helium inside the balloon compared to the weight of the air it displaces. Therefore, the overall force acting on the balloon is upward, causing it to ascend into the sky.