Happy Friday, and the weekly "A Taste of Physics" corner is back — number 47.
This time: a monstrous metal ball, and its connection to swimming pools and tennis rackets.
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The enormous metal ball in the video weighs 660 tons and hangs between floors 87 and 92 of the Taipei 101 tower in Taiwan.
Taipei 101 is a skyscraper standing 509 meters tall with 101 floors, which held the title of the world's tallest structure for several years.
The ball's purpose is to stabilize the building during earthquakes and typhoons — events that are quite common in Taiwan's capital.
But how does it work?
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Every material has a natural frequency at which it responds in a periodic, resonant way (a topic we've covered in this corner before).
Think of it like a playground swing. If you push the swing again and again each time it comes back to you, its oscillation will grow stronger and stronger.
If you push it at intervals that don't match its natural frequency, the swing will slow down.
A building that perfectly resonates with the wind striking it will sway more and more until it collapses.
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The ball acts as a damper thanks to its enormous mass, and it draws on two physical principles to prevent the building from swaying.
The first principle is conservation of energy.
Moving a metal ball of this weight requires it to absorb a tremendous amount of kinetic energy from the building, thereby slowing it down.
The ball also converts some of that energy into heat through friction with the stabilizing pistons, dissipating it throughout the structure.
The second — and more important — principle is inertia.
The building begins to move under the force of the wind, but it takes some time before that motion overcomes the ball's inertia, so the ball starts moving later.
This time delay is precisely engineered so that the ball swings in the opposite direction to the building, stabilizing it in place.
The ball's position, mass, and cable length were all calculated with great precision to cancel out the building's resonance with wind and seismic activity.
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If you've ever wondered about the logic of placing enormous swimming pools on the rooftops of high-rise buildings, this is one of the reasons.
A square meter of water weighs one ton, and a full swimming pool is more than heavy enough to serve as an excellent damper.
Similar dampers can also be found in tennis rackets, where added weight at a precise location on the racket makes it more stable and accurate.
Shock absorbers in vehicles are a particularly well-established technology, but what sets the modern dampers found in certain cars apart is their ability to convert the energy they absorb into electrical energy.
In this way the benefit is twofold: ride quality improves, while the vehicle's battery is simultaneously charged with energy that would otherwise have been lost without this technology.
Shabbat Shalom 😊
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