When a balloon filled with helium rises, it gains potential energy, but this does not violate the law of energy conservation. The potential energy gained by the balloon is a result of the work done on it by the surrounding air and the energy stored in the helium.
Here's a breakdown of the process:
Buoyancy: The reason a helium-filled balloon rises is due to buoyancy. The density of helium is lower than the density of the surrounding air, so it experiences an upward buoyant force. This force is a result of the pressure difference between the top and bottom of the balloon.
Work Done: As the balloon rises, the surrounding air does work on the balloon. The air pushes against the bottom of the balloon, transferring energy to it. This work done by the air is what increases the balloon's potential energy.
Potential Energy Increase: The potential energy of an object increases as it moves higher in a gravitational field. In the case of the balloon, as it rises against gravity, the work done on it by the air is converted into potential energy. This potential energy is stored in the balloon and is a result of its position in the Earth's gravitational field.
So, the potential energy gained by the helium-filled balloon comes from the work done on it by the surrounding air. The energy is not created or destroyed but rather transferred from the air to the balloon, causing its potential energy to increase. This process obeys the law of energy conservation, which states that energy cannot be created or destroyed, but only transferred or transformed from one form to another.