Moon rover sped up vs Moon rover as is released by NASA

originally posted by: MarioOnTheFly
a reply to: OneBigMonkeyToo

so if I grab a hand of sand on both environments...and throw it in the air...the one on the Moon will fall right back on the surface as opposed to one on Earth where it...apparently just "suspends in midair" ?

Well...one learns something new every day.

Like most things, it can get a little complicated and you're attempting to over-simplify it which won't give you the right answer.

Why is a fall from a tall building usually fatal to a human but not to a mouse? Because the human and the mouse have different mass to surface area ratios and therefore different terminal velocities.

Are all sand particles the same size? No they are not, therefore you have the same thing going on with sand particles, the larger particles tend to have higher terminal velocities and fall to earth faster than the small particles because they have a relatively greater mass to surface area ratio.

So do the particles on Earth fall faster or slower?

This is the wrong question and if you ask the wrong question you'll probably get the wrong answer. The correct answer is the particles on earth fall both faster and slower, so this is probably why you're confused, the coarse particles fall faster due to Earth higher gravity and the small particles fall more slowly because in spite of the higher gravity, they act like they have little built-in parachutes due to their mass to surface area ratio. They fall more slowly for the same reason mice fall more slowly than humans at terminal velocity.

On the moon, all particles fall at exactly the same rate regardless of size, because there is no "parachute effect" or slower terminal velocities for smaller particles.

a reply to: Arbitrageur

Why is a fall from a tall building usually fatal to a human but not to a mouse? Because the human and the mouse have different mass to surface area ratios and therefore different terminal velocities.

a mouse will most probably die having fallen from a tall building. Unless under tall building you mean...under 5 meters high.

On the moon, all particles fall at exactly the same rate regardless of size, because there is no "parachute effect" or slower terminal velocities for smaller particles.

this is not the issue. The issue of the thread is...whether regolit particles should have stayed hanging longer in the air...then shown in the rover video, compared to the same situation on Earth. I claim that they should have.

You guys claim that on the Moon...these regolit particles will fall right down. Now, to be perfectly clear in my claim...this can never happen on a moon environment...unless you remove the kinetic force that propells the particles. Once propelled by a force...there is no way in hell they should fall faster then on Earth...or "right down"...

a reply to: MarioOnTheFly

What would happen to them then? Enlighten us.

a reply to: MarioOnTheFly

I'd say the first problem with your assumption is there is no air on the moon. Care to try again see its because there is no atmosphere lighter particles don't drift. Also don't get sand storms on thru moon either. Yet they happen on earth but according to you I guess they don't

a reply to: MarioOnTheFly

I'd also add here to help you with all the calculations you're about to provide that the 'kinetic force propelling the particles" is removed the second that those particles leave the rover wheel.

a reply to: Darkmadness

If that is true then it should happen with all videos with the rover, right?

originally posted by: MarioOnTheFly
a mouse will most probably die having fallen from a tall building. Unless under tall building you mean...under 5 meters high.

I had a cat that fell from the fourth floor (13 metres) of a building and didn't broke any thing. He was a little sore in the day after but lived several years after that.

A human falling from a fourth floor wouldn't be that lucky.

a reply to: OneBigMonkeyToo

I'd also add here to help you with all the calculations you're about to provide that the 'kinetic force propelling the particles" is removed the second that those particles leave the rover wheel.

true...but then you are left with inertia. Absent of atmosphere on the moon...and lower gravity. I just dont see it how anything can "drop down" upon being released. I certainly don t understand how it can drop faster then on Earth.

a reply to: dragonridr

I'd say the first problem with your assumption is there is no air on the moon.

I made no such assumption. Maybe you're thinking about this "whether regolit particles should have stayed hanging longer in the air"

"air" in this sentence was meant to say medium. In our case vacuum.

originally posted by: ArMaP

originally posted by: MarioOnTheFly
a mouse will most probably die having fallen from a tall building. Unless under tall building you mean...under 5 meters high.

I had a cat that fell from the fourth floor (13 metres) of a building and didn't broke any thing. He was a little sore in the day after but lived several years after that.

A human falling from a fourth floor wouldn't be that lucky.

well man...didnt you know...cats have 9 lives...

a reply to: MarioOnTheFly

You need to look up the definition of inertia and consider what external force might be acting on a soil particle in motion.

originally posted by: MarioOnTheFly
a reply to: OneBigMonkeyToo

I'd also add here to help you with all the calculations you're about to provide that the 'kinetic force propelling the particles" is removed the second that those particles leave the rover wheel.

true...but then you are left with inertia. Absent of atmosphere on the moon...and lower gravity. I just dont see it how anything can "drop down" upon being released. I certainly don t understand how it can drop faster then on Earth.

It drops down due to gravity.

Whether it was on the Moon or on Earth, gravity would begin pulling down on the dust particle as soon as it was thrown off of the surface. The dust particle's momentum and inertia would allow the particle to continue to move for a while, but gravity would eventually win out and pull it back down.

On Earth (or in a relatively thick atmosphere anywhere), there would be another factor in play: air resistance. A piece of paper - or even a fine dust particle in your house - can seem to float very slowly down to the ground, more slowly than a ball would fall....and that is due to air resistance. If I kicked up a lot of dust in a bone-dry field here on earth, a cloud of dust would remain hanging in the air for some time; that "hanging in the air" is due to air resistance. The thick air would be viscous enough to hold things with a large relative surface area (relative to mass) for a while, counteracting the force of gravity.

However, if we were to eliminate air resistance by trying to kick up dust in a vacuum chamber, that dust would not "hang in the air" - because there would virtually be no air in which the dust could hang. In that case (in a vacuum), whether on Earth or on the Moon, the main external force acting on the dust would be gravity. The particle in a vacuum would be sent on an initial path until gravity pulls it back down, resulting in a ballistic trajectory.

In a vacuum where air resistance could be eliminated, the gravity on The Earth would pull that dust down more quickly than on the moon because the Earth has a greater acceleration due to gravity (9.8 m/s² for the Earth; 1.6 m/s² for the Moon).

a reply to: chr0naut

Just for argument's sake, doesn't that further prove the OP's point? If speeding it up 3x makes it look unnatural, then it must not have been shot in an environment 1/3 of earth's gravity? Am I wrong? Who cares? We landed on the moon. End of story.

originally posted by: MarioOnTheFly

true...but then you are left with inertia. Absent of atmosphere on the moon...and lower gravity. I just dont see it how anything can "drop down" upon being released. I certainly don t understand how it can drop faster then on Earth.

it doesnt drop faster than on earth (assuming its also in a vacuum chamber on earth).. and when you say drop down do you mean drop down immediately after leaving the wheel or reach its apex then drop down?

or are you hinting that it never drops back down? meaning you believe the particles are being launched at escape velocity.

a reply to: MarioOnTheFly
Have you watched the lunar rover video (the original one, not the speeded-up)? I don't see why you would have a problem with what we're saying about the video, unless you're just hanging on particular words and phrasing.

The dust kicked up by the rover behaves exactly as it would in vacuum and 1/6th gravity. There is the initial kinetic energy, yes, and it makes the dust fly up, slow down, and then fall back due to gravity. It's just this happens differently to how it would be in our atmosphere. The fine dust doesn't get suspended in the air (because there is no air), so it falls straight back to the ground, with the speed determined by the Moon's gravity. There's nothing in the airless environment of the Moon to make it just hang around above surface. Inertia keeps the things moving, it doesn't make stuff hang around either.

All this is fairly basic stuff kids learn at school, and there's plentiful material on the Internet for those who want to catch up or learn more.



P.S. By the way, here's the culprit (a dark spot annotated as LRV, to the right of the Apollo Descent Stage), spotted by the Lunar Reconnaissance Orbiter: lroc.sese.asu.edu...

originally posted by: MarioOnTheFly
a reply to: Arbitrageur
this is not the issue. The issue of the thread is...whether regolit particles should have stayed hanging longer in the air...then shown in the rover video, compared to the same situation on Earth. I claim that they should have.

You guys claim that on the Moon...these regolit particles will fall right down. Now, to be perfectly clear in my claim...this can never happen on a moon environment...unless you remove the kinetic force that propells the particles. Once propelled by a force...there is no way in hell they should fall faster then on Earth...or "right down"...

I never claimed they "fall right down". If you kick them up with the tires, they follow a ballistic trajectory that can keep going up for a while before stopping their ascent and falling. But on the moon there is no "parachute-like" effect where they linger a long time in the air as they fall because there's no air to cause them to do that.

originally posted by: MarioOnTheFly
a reply to: Arbitrageur
a mouse will most probably die having fallen from a tall building. Unless under tall building you mean...under 5 meters high.

originally posted by: ArMaP

originally posted by: MarioOnTheFly
a mouse will most probably die having fallen from a tall building. Unless under tall building you mean...under 5 meters high.

I had a cat that fell from the fourth floor (13 metres) of a building and didn't broke any thing. He was a little sore in the day after but lived several years after that.

A human falling from a fourth floor wouldn't be that lucky.

That's an anecdote but there is research showing about a 90% survival rate for cats falling from buildings, so it's no exception. Mice have an even lower terminal velocity so their survival rate should be even higher, and you're right humans don't fare very well on long falls. These are approximate terminal velocities for a "flat fall" (belly down):

human skydiver: ~200kph (~120mph)
cat: ~100kph (~60mph)
mouse: ~20kph (~12mph)

Quite interesting facts about cats

A 1987 paper in the Journal of the American Veterinary Medical Association studied 132 cases of falling cats. Ninety per cent survived; the average number of injuries per cat peaked at the seven-storey mark. There are cats that have fallen 30 storeys or more without ill effects.

The terminal velocity of tiny dust particles is really small, the dust can seem to "hang" in the air for a long time, but of course that can't happen on the moon.

a reply to: Arbitrageur

The terminal velocity of tiny dust particles is really small, the dust can seem to "hang" in the air for a long time, but of course that can't happen on the moon.

With fine enough dust terminal velocity is irrelevant. Brownian motion takes over, getting knocked around by air molecules, in essence levitating the dust. This won't happen on the Moon.





Neither will this.


Want to give jumping out of a 50' tree a shot?

originally posted by: Phage
a reply to: Arbitrageur
With fine enough dust terminal velocity is irrelevant. Brownian motion takes over, getting knocked around by air molecules, in essence levitating the dust. This won't happen on the Moon.

That's true. This amazes me even more. Even though it doesn't defy known physics, it's still quite amazing to me that Saharan dust can "defy gravity" for 5000 miles on Earth:

Saharan Dust From Africa Brings Hazy Skies to Texas Gulf Coast

Plumes of dust from the Sahara Desert frequently make a 5,000-mile-long voyage to parts of the United States and the air that lofts these particles can have a big impact on the Atlantic hurricane season.

Known as the Saharan air layer (SAL), this dry, dusty air mass pushes westward off Africa into the tropical Atlantic Ocean about every three to five days from late spring through early fall.

There can be a lot of that dust traveling 5000 miles depending on conditions, so yes it's not following a ballistic trajectory at all like dust on the moon does.

originally posted by: neveroddoreven99
a reply to: chr0naut

Just for argument's sake, doesn't that further prove the OP's point? If speeding it up 3x makes it look unnatural, then it must not have been shot in an environment 1/3 of earth's gravity? Am I wrong? Who cares? We landed on the moon. End of story.

That was precisely my point, but as Phage pointed out, it's really 1/6 th of Earths gravity.

If you had to speed up the film to make the gravitational effects look more 'Earthlike', the speed that the buggy moves and turns at would be way too fast - an indication that it wasn't filmed somewhere on Earth.

originally posted by: Arbitrageur

originally posted by: Phage
a reply to: Arbitrageur
With fine enough dust terminal velocity is irrelevant. Brownian motion takes over, getting knocked around by air molecules, in essence levitating the dust. This won't happen on the Moon.

That's true. This amazes me even more. Even though it doesn't defy known physics, it's still quite amazing to me that Saharan dust can "defy gravity" for 5000 miles on Earth:

Saharan Dust From Africa Brings Hazy Skies to Texas Gulf Coast

Plumes of dust from the Sahara Desert frequently make a 5,000-mile-long voyage to parts of the United States and the air that lofts these particles can have a big impact on the Atlantic hurricane season.

Known as the Saharan air layer (SAL), this dry, dusty air mass pushes westward off Africa into the tropical Atlantic Ocean about every three to five days from late spring through early fall.

There can be a lot of that dust traveling 5000 miles depending on conditions, so yes it's not following a ballistic trajectory at all like dust on the moon does.

Us Londoners have woken up a handful of times in the last 15 years to a light dusting on all the cars and surfaces outside. Dust from the Sahara. Really amazing.

If only chemtrail believers would take note of how long particulates can stay afloat and how far they can travel.

No one is chemtrailing over Tangiers in order to cover London.

I used to live in Saudi Arabia and vividly remember falling asleep with the window ajar, only to wake up with my bed and room covered in sand. Not a mistake one makes often.