A hydrogen-filled balloon stops rising after it has attained a certain height in the sky. This happens because

A hydrogen-filled balloon stops rising after it has attained a certain height in the sky due to the balance between the buoyant force and the force of gravity.

Here are the steps to understand this:

1. When a balloon is filled with hydrogen, it becomes lighter than the air around it. This is because hydrogen is less dense than air.

2. As a result, the balloon experiences a buoyant force which pushes it upwards. This force is due to the difference in pressure between the bottom and the top of the balloon.

3. As the balloon rises, the air pressure decreases. This means the difference in pressure between the bottom and the top of the balloon also decreases, which in turn reduces the buoyant force.

4. At the same time, the balloon is always subject to the force of gravity, which pulls it downwards.

5. At a certain height, the buoyant force equals the force of gravity. When this happens, the balloon stops rising because there is no net force pushing it upwards.

6. Therefore, a hydrogen-filled balloon stops rising after it has attained a certain height in the sky because the buoyant force and the force of gravity balance each other out.

A hydrogen-filled balloon stops rising after it has attained a certain height in the sky. This happens because of the principle of buoyancy. Buoyancy is the upward force exerted on an object immersed in a fluid, such as air. In the case of a balloon, the hydrogen gas inside the balloon is less dense than the surrounding air. This means that the upward buoyant force acting on the balloon is greater than the downward force of gravity. As a result, the balloon rises in the sky.

However, as the balloon continues to rise, the atmospheric pressure decreases. This decrease in pressure causes the hydrogen gas inside the balloon to expand. As the gas expands, it becomes less dense compared to the surrounding air. Eventually, the density of the hydrogen gas inside the balloon becomes equal to the density of the surrounding air. At this point, the upward buoyant force is no longer greater than the downward force of gravity, and the balloon stops rising.

In summary, a hydrogen-filled balloon stops rising in the sky because the density of the hydrogen gas inside the balloon becomes equal to the density of the surrounding air, resulting in a balance of forces.