APOD: Solar System Ball Drop (2021 Aug 25)

[APOD Robot]

Solar System Ball Drop

Explanation: Does a ball drop faster on Earth, Jupiter, or Uranus? The featured animation shows a ball dropping from one kilometer high toward the surfaces of famous solar system bodies, assuming no air resistance. The force of gravity depends on the mass of the attracting object, with higher masses pulling down with greater forces. But gravitational force also depends on distance from the center of gravity, with shorter distances causing the ball to drop faster. Combining both mass and distance, it might be surprising to see that Uranus pulls the ball down slightly slower than Earth, despite containing over 14 times more mass. This happens because Uranus has a much lower density, which puts its cloud tops further away from its center of mass. Although the falling ball always speeds up, if you were on the ball you would not feel this acceleration because you would be in free-fall. Of the three planets mentioned, the video demonstrates a ball drops even faster on Jupiter than either Earth and Uranus.

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[SpaceCadet]

Does the slower fall speed make it safer for a person to fall that distance?

[Ann]

Click to play embedded YouTube video.

Click to play embedded YouTube video.

And here I've always been told that heavy and lightweight objects fall at the same speed...

Of course, I wasn't considering objects falling on different bodies in the Solar system...

Ann

[JohnD]

Does the slower fall speed make it safer for a person to fall that distance?

SC,
You will note, if you watched the video, that even onto Ceres that has the lowest g used, the terminal velocity was 90kph, or 55mph. All others were in hundreds of kph. Since your falling astronaut will lack the security of a car shell, seats and seat belts, they must be considered to have the same risk as a pedestrian hit by a car at that speed. Hit at 90kph, the probability of death is 1. They will die. Even on Earth. The damage to their space suit is incidental - they will die from impact, and then from vacuum, cold and hypoxia.

John

[orin stepanek]

Interesting that on Earth objects drop faster than on Uranus; yet it takes more thrust to reach the escape velocity on Uranus than on Earth!
ESCAPE VELOCITY
76,968km/h; Uranus
40,284km/h; Earth

Now this kitty is a Cool Cat

[Cousin Ricky]

I’m impressed that they used a realistic color for the Sun and showed Venus with its clouds.

[E Fish]

I love this video! I think I need to use it in my class when I talk about gravity. It's a vivid example of how it works on bodies of different masses.

Now, they need to make another one with balls dropping to other types of objects like onto a neutron star or something. I read a description once that a marshmallow would hit the surface of a neutron star with the force an H-bomb.

[neufer]

Does the slower fall speed make it safer for a person to fall that distance?

You will note, if you watched the video, that even onto Ceres that has the lowest g used, the terminal velocity was 90kph, or 55mph. All others were in hundreds of kph. Since your falling astronaut will lack the security of a car shell, seats and seat belts, they must be considered to have the same risk as a pedestrian hit by a car at that speed. Hit at 90kph, the probability of death is 1. They will die. Even on Earth. The damage to their space suit is incidental - they will die from impact, and then from vacuum, cold and hypoxia.

• The terminal velocity on Venus is just 15-20 mph ...
  so one is unlikely to die from impact, vacuum, cold or hypoxia.

[Chris Peterson]

Does the slower fall speed make it safer for a person to fall that distance?

You will note, if you watched the video, that even onto Ceres that has the lowest g used, the terminal velocity was 90kph, or 55mph. All others were in hundreds of kph. Since your falling astronaut will lack the security of a car shell, seats and seat belts, they must be considered to have the same risk as a pedestrian hit by a car at that speed. Hit at 90kph, the probability of death is 1. They will die. Even on Earth. The damage to their space suit is incidental - they will die from impact, and then from vacuum, cold and hypoxia.

• The terminal velocity on Venus is just 15-20 mph ...
  so one is unlikely to die from impact, vacuum, cold or hypoxia.

Just pressure, heat, and acidic dissolution?

The Universe provides so many opportunities for exciting exits!

[JohnD]

Does the slower fall speed make it safer for a person to fall that distance?

You will note, if you watched the video, that even onto Ceres that has the lowest g used, the terminal velocity was 90kph, or 55mph. All others were in hundreds of kph. Since your falling astronaut will lack the security of a car shell, seats and seat belts, they must be considered to have the same risk as a pedestrian hit by a car at that speed. Hit at 90kph, the probability of death is 1. They will die. Even on Earth. The damage to their space suit is incidental - they will die from impact, and then from vacuum, cold and hypoxia.

• The terminal velocity on Venus is just 15-20 mph ...
  so one is unlikely to die from impact, vacuum, cold or hypoxia.

Did you work it out, Neufer? Vt = SQR((4gd/3Cd)((ps - p)/p)) is a formidable equation! Not one I'm going to take on without a whip and a chair (To poke at it, not sit on!)
Various online estimates, without showing their working, of about 20mph, 10meters/second. Parachutists land at about 6m/s, so our intrepid, free falling astronaut might expect a broken ankle or two. If their kit was up to the conditions listed by Chris, and the impact (they would need to stay upright, not roll over, I fear) they yes, they might survive. But only from an atmosphere many times denser than the Earth's, not because of less 'g'.

John

[Chris Peterson]

You will note, if you watched the video, that even onto Ceres that has the lowest g used, the terminal velocity was 90kph, or 55mph. All others were in hundreds of kph. Since your falling astronaut will lack the security of a car shell, seats and seat belts, they must be considered to have the same risk as a pedestrian hit by a car at that speed. Hit at 90kph, the probability of death is 1. They will die. Even on Earth. The damage to their space suit is incidental - they will die from impact, and then from vacuum, cold and hypoxia.

• The terminal velocity on Venus is just 15-20 mph ...
  so one is unlikely to die from impact, vacuum, cold or hypoxia.

Did you work it out, Neufer? Vt = SQR((4gd/3Cd)((ps - p)/p)) is a formidable equation! Not one I'm going to take on without a whip and a chair (To poke at it, not sit on!)
Various online estimates, without showing their working, of about 20mph, 10meters/second. Parachutists land at about 6m/s, so our intrepid, free falling astronaut might expect a broken ankle or two. If their kit was up to the conditions listed by Chris, and the impact (they would need to stay upright, not roll over, I fear) they yes, they might survive. But only from an atmosphere many times denser than the Earth's, not because of less 'g'.

John

Today's APOD concerns just the effect of gravity, with atmospheric drag removed. Art's response was to your misuse of "terminal velocity", which does not apply in the context of today's post.

[neufer]

Now, they need to make another one with balls dropping to other types of objects like onto a neutron star or something. I read a description once that a marshmallow would hit the surface of a neutron star with the force an H-bomb.

• An A-bomb not an H-bomb.

1 regular marshmallow weighs 7 grams or an energy
of mc² = 630 terajoule (TJ) = 200,000 tons of TNT

A marshmallow landing on a neutron star might release ~250 TJ
= 60,000 tons of TNT => a large fission ("atomic") bomb (s'more or less).

[A marshmallow dropping one kilometer might release 5,000 tons of TNT.]

The amount of energy released by fission bombs can range
from just under a ton to upwards of 500,000 tons of TNT

A thermonuclear [H-bomb] weapon weighing little more than 2,400 pounds
can release energy equal to more than 5,000 TJ (1.2 Megatons of TNT).

<<The terajoule (TJ) is equal to one trillion (10¹²) joules; or about 0.278 GWh. About 63 TJ of energy was released by Little Boy. The International Space Station, with a mass of approximately 450 megagrams and orbital velocity of 7700 m/s, has a kinetic energy of roughly 13 TJ. In 2017, Hurricane Irma was estimated to have a peak wind energy of 112 TJ. 90 TJ is about the amount of energy equivalent to 1 gram of mass.>>

[xuxu]

Great post.. any chance you could post a simulation of how fast each planet goes around the sun and maybe the speed of each ones rotation?
Thanks

[johnnydeep]

Now, they need to make another one with balls dropping to other types of objects like onto a neutron star or something. I read a description once that a marshmallow would hit the surface of a neutron star with the force an H-bomb.

• An A-bomb not an H-bomb.

1 regular marshmallow weighs 7 grams or an energy
of mc² = 630 terajoule (TJ) = 200,000 tons of TNT

A marshmallow landing on a neutron star might release ~250 TJ
= 60,000 tons of TNT => a large fission ("atomic") bomb (s'more or less).

[A marshmallow dropping one kilometer might release 5,000 tons of TNT.]

I don't follow. What's the difference between "a marshmallow landing on" and "a marshmallow dropping one km"? The energy released by "landing on" is determined by the velocity of impact. Is the energy released by dropping 1 km due to the difference in gravitational potential? ...Oh, are you saying that the marshmallow would release the combined energy of the impact plus the difference in gravitational potential?

[Fred the Cat]

Brings forward memories of the cliff divers on Miranda.

Those will be the days.

[JohnD]

"The energy released by "landing on" is determined by the velocity of impact."

Surely, 'times the mass of the object', Johnny? I'll bet that David Scott's hammer made a bigger hole in the moon dust than the feather! Same velocity, more energy.
John

PS Fred, your links seem out of date - they don't mention cliff diving or Miranda, unless its in the small print. This reckons that you would hit the bottom at 200 kps, as Miranda has twice the mass (?) of Ceres: https://www.youtube.com/watch?v=gQjs366 ... nel=Astrum J

[ta152h0]

I think it was Alan Shepherd who dropped the feather and a hammer on the moon surface. Didn't he sneak a golf ball/club on the moon? pass the ice cold one

[Chris Peterson]

"The energy released by "landing on" is determined by the velocity of impact."

Surely, 'times the mass of the object', Johnny? I'll bet that David Scott's hammer made a bigger hole in the moon dust than the feather! Same velocity, more energy.
John

The speed and the mass, of course. But the speed often is the most important factor, since its component is squared. But clearly if you have two bodies hit at the same speed, the energy difference is determined only by mass.

[JohnD]

ta152h20,
No, it was David Scott.

Aren't some web searchers weird? To check quickly, I entered "moon feather hammer", not into my usual (couldn't be &rs%d to get that out) and the first entry was "Love Honey Fetish Selection. See Our Latest Fetish Wear." !?!?!?

John

[Chris Peterson]

ta152h20,
No, it was David Scott.

Aren't some web searchers weird? To check quickly, I entered "moon feather hammer", not into my usual (couldn't be &rs%d to get that out) and the first entry was "Love Honey Fetish Selection. See Our Latest Fetish Wear." !?!?!?

John

Hmm. When I put that search into Google I got the expected Apollo video at the top of the list. Google structures its search results based on what it thinks your interests are. So the question is... what else have you been searching for lately?

[neufer]

Now, they need to make another one with balls dropping to other types of objects like onto a neutron star or something. I read a description once that a marshmallow would hit the surface of a neutron star with the force an H-bomb.

• An A-bomb not an H-bomb.

1 regular marshmallow weighs 7 grams or an energy
of mc² = 630 terajoule (TJ) = 200,000 tons of TNT

A marshmallow landing on a neutron star might release ~250 TJ
= 60,000 tons of TNT => a large fission ("atomic") bomb (s'more or less).

[A marshmallow dropping one kilometer might release 5,000 tons of TNT.]

I don't follow. What's the difference between "a marshmallow landing on" and "a marshmallow dropping one km"? The energy released by "landing on" is determined by the velocity of impact. Is the energy released by dropping 1 km due to the difference in gravitational potential? ...Oh, are you saying that the marshmallow would release the combined energy of the impact plus the difference in gravitational potential?

"E Fish" read "a description once that a marshmallow would
hit the surface of a neutron star with the "force" [sic] an H-bomb".

Presumably, that involved a marshmallow with escape velocity.

The current discussion only involves dropping things from a height of 1 km
(such that it will not approach escape velocity at impact).

In any event, the marshmallow will have a maximum energy release of no more
than a 200 kt "A" bomb (; nevertheless, one should avoid the extra calories if possible).

[Lehmbja249]

If gravity is different then will it have less disasters

[johnnydeep]

• An A-bomb not an H-bomb.

1 regular marshmallow weighs 7 grams or an energy
of mc² = 630 terajoule (TJ) = 200,000 tons of TNT

A marshmallow landing on a neutron star might release ~250 TJ
= 60,000 tons of TNT => a large fission ("atomic") bomb (s'more or less).

[A marshmallow dropping one kilometer might release 5,000 tons of TNT.]

I don't follow. What's the difference between "a marshmallow landing on" and "a marshmallow dropping one km"? The energy released by "landing on" is determined by the velocity of impact. Is the energy released by dropping 1 km due to the difference in gravitational potential? ...Oh, are you saying that the marshmallow would release the combined energy of the impact plus the difference in gravitational potential?

"E Fish" read "a description once that a marshmallow would
hit the surface of a neutron star with the "force" [sic] an H-bomb".

Presumably, that involved a marshmallow with escape velocity.

The current discussion only involves dropping things from a height of 1 km
(such that it will not approach escape velocity at impact).

In any event, the marshmallow will have a maximum energy release of no more
than a 200 kt "A" bomb (; nevertheless, one should avoid the extra calories if possible).

Sorry, but this didn't help me. Now we have three numbers: 60 kilotons (impacting), 5 kilotons (dropping 1 km) and 200 kilotons (e=mc²), the first two resulting from a 7 gram marshmallow doing something in the vicinity of a neutron star.

[johnnydeep]

"The energy released by "landing on" is determined by the velocity of impact."

Surely, 'times the mass of the object', Johnny? I'll bet that David Scott's hammer made a bigger hole in the moon dust than the feather! Same velocity, more energy.
John

Surely. I didn't mention the mass because we were already talking about a 7 gm marshmallow. Or I was anyway.

[Chris Peterson]

I don't follow. What's the difference between "a marshmallow landing on" and "a marshmallow dropping one km"? The energy released by "landing on" is determined by the velocity of impact. Is the energy released by dropping 1 km due to the difference in gravitational potential? ...Oh, are you saying that the marshmallow would release the combined energy of the impact plus the difference in gravitational potential?

"E Fish" read "a description once that a marshmallow would
hit the surface of a neutron star with the "force" [sic] an H-bomb".

Presumably, that involved a marshmallow with escape velocity.

The current discussion only involves dropping things from a height of 1 km
(such that it will not approach escape velocity at impact).

In any event, the marshmallow will have a maximum energy release of no more
than a 200 kt "A" bomb (; nevertheless, one should avoid the extra calories if possible).

Sorry, but this didn't help me. Now we have three numbers: 60 kilotons (impacting), 5 kilotons (dropping 1 km) and 200 kilotons (e=mc²), the first two resulting from a 7 gram marshmallow doing something in the vicinity of a neutron star.

If there is no impact, there is no energy release. Just a transfer of gravitational potential energy to kinetic energy, fully contained within the body.