PBS Space Time Season 2015 Episode 19 Challenge: What Happens to a Helium Balloon in Freefall?

PBS Space Time season 2015 episode 19, titled Challenge: What Happens to a Helium Balloon in Freefall?, explores the physics behind a seemingly simple question: what happens to a helium balloon when it is dropped and allowed to fall freely? The episode starts by addressing the basics of gravity and the forces that act on a falling object. The narrator explains that objects in freefall experience an acceleration of 9.8 meters per second squared due to gravity, and that there are no additional forces acting on the object, such as air resistance, when it is dropped in a vacuum.

From here, the episode sets out to answer the titular challenge: what happens to a helium balloon when it is dropped? To answer this question, the host of PBS Space Time, Matt O'Dowd, enlists the help of a special guest: Derek Muller, the host of the YouTube channel Veritasium. Together, O'Dowd and Muller set up a series of experiments to test what happens to a helium balloon in freefall, using a high-altitude weather balloon to lift the balloons to a high altitude before releasing them.

In the first experiment, O'Dowd and Muller attach a camera to a helium balloon and release it from the weather balloon. The camera captures footage of the balloon as it falls rapidly towards the ground, and the hosts note that the balloon appears to be falling at the same speed as the surrounding air. Muller points out that this is because the helium inside the balloon is no longer exerting an upward force on the balloon, as there is no longer a pressure difference between the inside and outside of the balloon due to the lack of air resistance.

In the second experiment, O'Dowd and Muller release two balloons at once: one filled with helium, and one filled with air. The results of this experiment are surprising: the helium balloon falls faster than the air-filled balloon, despite the fact that the helium balloon is still falling at the same speed as the surrounding air. The hosts explain that this is due to the difference in density between the helium and the surrounding air: because the helium is less dense than the air, it takes up more volume and experiences more air resistance as it falls, slowing it down compared to the air-filled balloon.

In the third experiment, O'Dowd and Muller modify the second experiment by attaching a parachute to the helium balloon. This time, the helium balloon falls more slowly than the air-filled balloon, despite the fact that it is still falling at the same speed as the surrounding air. The hosts explain that this is due to the parachute creating more air resistance, which slows down the helium balloon more than the air-filled balloon.

Throughout the episode, O'Dowd and Muller use their experiments to illustrate key concepts in physics, such as air resistance, density, and pressure. They also show how small changes in a system can have a big impact on how it behaves, such as the addition of a parachute drastically slowing down the fall of a helium balloon.

Overall, PBS Space Time season 2015 episode 19 is an informative and engaging exploration of the physics of falling objects, using a simple question about helium balloons to illustrate complex concepts in an approachable way. Whether you're a student studying physics or just someone with a curious mind, this episode is sure to teach you something new about the world around you.