4 ms·

Why is the velocity of a falling bullet > the speed of gravity?

by cyberCleve 4y ago

philwelch 4y ago
Gravity isn’t a speed, it’s a force.
- nobody9999 4y ago
  >Gravity isn’t a speed, it’s a force. Actually, it's not a force either[0]. It feels like a force, but it's just mass acting in warped space-time. [0] http://curious.astro.cornell.edu/about-us/140-physics/the-theory-of-relativity/general-relativity/1059-if-gravity-isn-t-a-force-how-does-it-accelerate-objects-advanced http://curious.astro.cornell.edu/about-us/140-physics/the-th...
  - philwelch 4y ago
    I yield to your superior pedantry :) But seriously, thanks!
  - midoridensha 4y ago
    Only if you believe the theory of relativity is correct. If you believe in quantum mechanics or some other theory of gravity, this isn't true.
    - nobody9999 4y ago
      >Only if you believe the theory of relativity is correct. https://bohring.substack.com/p/how-do-we-know-that-general-relativity https://bohring.substack.com/p/how-do-we-know-that-general-r... https://en.wikipedia.org/wiki/Tests_of_general_relativity https://en.wikipedia.org/wiki/Tests_of_general_relativity https://www.researchgate.net/post/Why_you_think_that_general_theory_of_relativity_is_wrong_or_incomplete https://www.researchgate.net/post/Why_you_think_that_general... https://archive.ph/iVZZu https://archive.ph/iVZZu https://www.livescience.com/black-hole-image-shows-einstein-right-again.html https://www.livescience.com/black-hole-image-shows-einstein-... Und so weiter, und so weiter...
      - midoridensha 4y ago
        I can show you plenty of tests "proving" that Newtonian mechanics are correct too. General relativity doesn't correctly predict things at quantum scale.
vlovich123 4y ago
Gravity doesn’t have a speed. It creates an acceleration due to force. The bullet is accelerating over a great distance until it reaches terminal velocity (where the air resistance counterbalances any gains in acceleration). The easiest way to think about it is in terms of conservation of energy. All the kinetic energy the bullet has at the muzzle is converted into gravitational potential until velocity hits zero. At that point, gravitational velocity starts getting converted directly back into kinetic energy. If not for air resistance, the bullet would reach the ground at roughly muzzle velocity. However, air resistance on the way up zaps some of that energy and presents a velocity barrier on the way down.
sobriquet9 4y ago
There are two components - horizontal and vertical. For a bullet fired straight up, horizontal component is negligible, as the bullet will spend enough time in flight for it to decrease due to air resistance. The vertical component is primarily determined by sectional density. Tumbling bullet spends a lot of time flying sideways, so its terminal velocity (where air resistance equals weight) is way less than muzzle velocity.
renewiltord 4y ago
It's not. The magnitude of the velocity of a falling bullet (in the low m/s) is many orders of magnitude lower than the speed of gravity (which propagates at the speed of light)
magicalhippo 4y ago
By "speed of gravity" I assume you mean terminal velocity[1]. If not fired fairly straight up the bullet can maintain a ballistic trajectory[2], rather than being in a vertical free fall. In that case, the higher speed compared to the terminal velocity is simply because it has yet to shed the speed it acquired[3] when it was accelerated out of the barrel. [1]: https://en.wikipedia.org/wiki/Terminal_velocity https://en.wikipedia.org/wiki/Terminal_velocity [2]: https://en.wikipedia.org/wiki/Ballistics https://en.wikipedia.org/wiki/Ballistics [3]: https://en.wikipedia.org/wiki/Muzzle_velocity https://en.wikipedia.org/wiki/Muzzle_velocity

Why is the velocity of a falling bullet > the speed of gravity?

philwelch 4y ago

Gravity isn’t a speed, it’s a force.

nobody9999 4y ago
>Gravity isn’t a speed, it’s a force. Actually, it's not a force either[0]. It feels like a force, but it's just mass acting in warped space-time. [0] http://curious.astro.cornell.edu/about-us/140-physics/the-theory-of-relativity/general-relativity/1059-if-gravity-isn-t-a-force-how-does-it-accelerate-objects-advanced http://curious.astro.cornell.edu/about-us/140-physics/the-th...
- philwelch 4y ago
  I yield to your superior pedantry :) But seriously, thanks!
- midoridensha 4y ago
  Only if you believe the theory of relativity is correct. If you believe in quantum mechanics or some other theory of gravity, this isn't true.
  - nobody9999 4y ago
    >Only if you believe the theory of relativity is correct. https://bohring.substack.com/p/how-do-we-know-that-general-relativity https://bohring.substack.com/p/how-do-we-know-that-general-r... https://en.wikipedia.org/wiki/Tests_of_general_relativity https://en.wikipedia.org/wiki/Tests_of_general_relativity https://www.researchgate.net/post/Why_you_think_that_general_theory_of_relativity_is_wrong_or_incomplete https://www.researchgate.net/post/Why_you_think_that_general... https://archive.ph/iVZZu https://archive.ph/iVZZu https://www.livescience.com/black-hole-image-shows-einstein-right-again.html https://www.livescience.com/black-hole-image-shows-einstein-... Und so weiter, und so weiter...
    - midoridensha 4y ago
      I can show you plenty of tests "proving" that Newtonian mechanics are correct too. General relativity doesn't correctly predict things at quantum scale.

vlovich123 4y ago

Gravity doesn’t have a speed. It creates an acceleration due to force. The bullet is accelerating over a great distance until it reaches terminal velocity (where the air resistance counterbalances any gains in acceleration). The easiest way to think about it is in terms of conservation of energy. All the kinetic energy the bullet has at the muzzle is converted into gravitational potential until velocity hits zero. At that point, gravitational velocity starts getting converted directly back into kinetic energy. If not for air resistance, the bullet would reach the ground at roughly muzzle velocity. However, air resistance on the way up zaps some of that energy and presents a velocity barrier on the way down.

sobriquet9 4y ago

There are two components - horizontal and vertical. For a bullet fired straight up, horizontal component is negligible, as the bullet will spend enough time in flight for it to decrease due to air resistance. The vertical component is primarily determined by sectional density. Tumbling bullet spends a lot of time flying sideways, so its terminal velocity (where air resistance equals weight) is way less than muzzle velocity.

renewiltord 4y ago

It's not. The magnitude of the velocity of a falling bullet (in the low m/s) is many orders of magnitude lower than the speed of gravity (which propagates at the speed of light)

magicalhippo 4y ago

By "speed of gravity" I assume you mean terminal velocity[1]. If not fired fairly straight up the bullet can maintain a ballistic trajectory[2], rather than being in a vertical free fall. In that case, the higher speed compared to the terminal velocity is simply because it has yet to shed the speed it acquired[3] when it was accelerated out of the barrel. [1]: https://en.wikipedia.org/wiki/Terminal_velocity https://en.wikipedia.org/wiki/Terminal_velocity [2]: https://en.wikipedia.org/wiki/Ballistics https://en.wikipedia.org/wiki/Ballistics [3]: https://en.wikipedia.org/wiki/Muzzle_velocity https://en.wikipedia.org/wiki/Muzzle_velocity