3 ms·

There's no way it's 20-40 mph. They're dense enough for much higher velocities.

by bagels 3y ago

lethal-radio 3y ago
Confirmed on wolframalpha. Terminal velocity is about 9mph https://www.wolframalpha.com/input?i=terminal+velocity+of+an+iPhone&assumption=%7B%22F%22%2C+%22TimeToFall%3AWithDrag%22%2C+%22Cd%22%7D+-%3E%220.1%22&assumption=%7B%22F%22%2C+%22TimeToFall%3AWithDrag%22%2C+%22H%22%7D+-%3E%2212000+ft%22&assumption=%7B%22F%22%2C+%22TimeToFall%3AWithDrag%22%2C+%22d%22%7D+-%3E%2212000+ft%22&assumption=%7B%22F%22%2C+%22TimeToFall%3AWithDrag%22%2C+%22rho%22%7D+-%3E%221.29+kg%2Fm%5E3%22&assumption=%7B%22F%22%2C+%22TimeToFall%3AWithDrag%22%2C+%22A%22%7D+-%3E%221.28+m%5E2%22 https://www.wolframalpha.com/input?i=terminal+velocity+of+an...
- bagels 3y ago
  Exactly one iphone had a mass that low, 5s. None of them have >1m^2 surface area.
- tjmc 3y ago
  1.28sqm projected surface area? That's a very a big iphone.
  - xxs 3y ago
    >a very a big iphone. putting mildly, still it's lovely to see the mix the input of imperial and metric units. the 'fluid' density is quite wrong as well. 1.29 kg/m^3 -> almost 777 times lighter than water, it's similar to air. By its dimension iphone 15 should be around twice heavier than water.
- amelius 3y ago
  That's assuming the phone will fall while facing down with it's largest surface.
- amelius 3y ago
  9mph? Always carry an iPhone while on an airplane ...
kstrauser 3y ago
They’re also broad and flat, and very likely to tumble unaerodynamically on their way down.
sbuk 3y ago
~25mph assuming a Cd of 2.1 (a smooth brick is the closest I could find) a mass of 0.194Kg and a surface area of 0.01142313m^2 (75.6mm x 150.9mm). Of course that assumes it’s falling facing its largest surface, and not tumbling or a falling edge first. Obviously that is trickier to calculate, but 20-40mph doesn’t seem that unreasonable. Edit: it takes ~3 seconds to reach 99% terminal velocity.
- xxs 3y ago
  This feels like calculating a "spherical horse in a vacuum", except with drag this time.
  - sbuk 3y ago
    First Monday morning back email avoidance tactics ;)
  - peterleiser 3y ago
    Hah, yeah. But it's a good problem solving and reasoning exercise. One of my courses in college used this book and it's very useful for reasoning about general real-world science topics: https://uscibooks.aip.org/books/consider-a-spherical-cow-a-course-in-environmental-problem-solving/ https://uscibooks.aip.org/books/consider-a-spherical-cow-a-c...
- robertlagrant 3y ago
  > Of course that assumes it’s falling facing its largest surface That was what I was thinking: surely it wouldn't be stable falling face-first? Wouldn't it be more likely to either tumble or settle on an edge?
  - cesarb 3y ago
    > Wouldn't it be more likely to either tumble or settle on an edge? There's also the possibility that it behaves more like an airfoil, and starts generating lift once it's going fast enough.

There's no way it's 20-40 mph. They're dense enough for much higher velocities.

by bagels 3y ago

There's no way it's 20-40 mph. They're dense enough for much higher velocities.

Confirmed on wolframalpha. Terminal velocity is about 9mph https://www.wolframalpha.com/input?i=terminal+velocity+of+an+iPhone&assumption=%7B%22F%22%2C+%22TimeToFall%3AWithDrag%22%2C+%22Cd%22%7D+-%3E%220.1%22&assumption=%7B%22F%22%2C+%22TimeToFall%3AWithDrag%22%2C+%22H%22%7D+-%3E%2212000+ft%22&assumption=%7B%22F%22%2C+%22TimeToFall%3AWithDrag%22%2C+%22d%22%7D+-%3E%2212000+ft%22&assumption=%7B%22F%22%2C+%22TimeToFall%3AWithDrag%22%2C+%22rho%22%7D+-%3E%221.29+kg%2Fm%5E3%22&assumption=%7B%22F%22%2C+%22TimeToFall%3AWithDrag%22%2C+%22A%22%7D+-%3E%221.28+m%5E2%22 https://www.wolframalpha.com/input?i=terminal+velocity+of+an...

bagels 3y ago
Exactly one iphone had a mass that low, 5s. None of them have >1m^2 surface area.
tjmc 3y ago
1.28sqm projected surface area? That's a very a big iphone.
- xxs 3y ago
  >a very a big iphone. putting mildly, still it's lovely to see the mix the input of imperial and metric units. the 'fluid' density is quite wrong as well. 1.29 kg/m^3 -> almost 777 times lighter than water, it's similar to air. By its dimension iphone 15 should be around twice heavier than water.
amelius 3y ago
That's assuming the phone will fall while facing down with it's largest surface.
amelius 3y ago
9mph? Always carry an iPhone while on an airplane ...

kstrauser 3y ago

They’re also broad and flat, and very likely to tumble unaerodynamically on their way down.

sbuk 3y ago

~25mph assuming a Cd of 2.1 (a smooth brick is the closest I could find) a mass of 0.194Kg and a surface area of 0.01142313m^2 (75.6mm x 150.9mm). Of course that assumes it’s falling facing its largest surface, and not tumbling or a falling edge first. Obviously that is trickier to calculate, but 20-40mph doesn’t seem that unreasonable. Edit: it takes ~3 seconds to reach 99% terminal velocity.

xxs 3y ago
This feels like calculating a "spherical horse in a vacuum", except with drag this time.
- sbuk 3y ago
  First Monday morning back email avoidance tactics ;)
- peterleiser 3y ago
  Hah, yeah. But it's a good problem solving and reasoning exercise. One of my courses in college used this book and it's very useful for reasoning about general real-world science topics: https://uscibooks.aip.org/books/consider-a-spherical-cow-a-course-in-environmental-problem-solving/ https://uscibooks.aip.org/books/consider-a-spherical-cow-a-c...
robertlagrant 3y ago
> Of course that assumes it’s falling facing its largest surface That was what I was thinking: surely it wouldn't be stable falling face-first? Wouldn't it be more likely to either tumble or settle on an edge?
- cesarb 3y ago
  > Wouldn't it be more likely to either tumble or settle on an edge? There's also the possibility that it behaves more like an airfoil, and starts generating lift once it's going fast enough.