Were the Lunar Rovers faked?

[Glom]

In Zero G, an object with a mass of 1kg has a weight of 0kg

In zero g, the weight of 1kg is 0 netwons.

Funny thing is, we can fix that one in another way as well.

"In Zero G, an object with a mass of 1kg has the weight of an object with a mass of 0kg" 

But in what gravitational field, sir, what gravitational field?

The kilogram-force is sometimes used in an effort to be annoying and that is 9.81N, basically the weight of 1kg in Earth standard gravity.

If it must be used, qualify the symbol by writing is as kgf.

[Not Myself]

In Zero G, an object with a mass of 1kg has a weight of 0kg

In zero g, the weight of 1kg is 0 netwons.

Funny thing is, we can fix that one in another way as well.

"In Zero G, an object with a mass of 1kg has the weight of an object with a mass of 0kg" 

But in what gravitational field, sir, what gravitational field?

In any Zero G gravitational field!  One without even tidal forces.

[Donnie B.]

But if it has the weight of an object with 0kg mass, it must be moving at the speed of light!

[cjameshuff]

Do we even have a citation for the loading limits of the LRV? Or is it just a bit of hyperbole taken too literally, which is often a trap HBs fall into.

All I've seen is a vague "it is often said" statement that it wouldn't support the astronauts on Earth, and a completely unsupported claim that this means it couldn't withstand the impact of an astronaut falling a short distance on the moon.

First, it's entirely possible that the rover never experienced forces in excess of six times its static load. There's plenty of margin there to bring the falling astronauts to a halt in a reasonable distance. If the flexing rover exerted a continuous upward force of 5 times the astronauts lunar weight as it compressed underneath them, it would bring them to a halt in 1/4 the distance they fell without ever exerting as much force as would be needed to support them on Earth...and the actual thing had a very flexible structure with soft wheels and suspension.

However, it needn't be even that limited. The rover's a massive, damped elastic structure. It's entirely reasonable for the rover to withstand forces for a brief period that it could not withstand continuously, it just needs to bring the landing object to a halt before it gets permanently deformed by those forces. A 500 g stone dropped onto the rover from 1 m, being brought to a halt in 1 millisecond by the impact, would briefly apply the same force as a 550 kg object resting on the rover, but the rover is obviously not going to react in the same way. The rover would flex and compress in response to the astronaut landing on it, but the force between the rover and the astronaut would drop to the astronaut's lunar weight as it did so. The same goes for travel over bumpy terrain...the peak force experienced during a bump could easily exceed the maximum static force the rover could withstand, but not be sustained over enough distance to irreversibly deform the rover's structure.

So...yes, anywho, you do need to give numbers showing that the rover couldn't operate on the moon. Show it couldn't withstand the dynamic loads involved. A vague statement by a non-authoritative source about its behavior under static loads in an environment with six times the gravitational acceleration does not qualify.

[Not Myself]

Yes, I guess the slightest force would do that.

Have you seen my new 0kg virtual car keys?  Oh, there they are, on the table.  No wait, don't touch them, oh - bugger, gone!

[Tedward]

To sum the claim up then.

My gut feeling says no and I think you should agree with me? (My as in OP claim)

Been having a look around in my un expert way.

Drive Ratio 80:1. RPM max 10,000. Wheel diameter 32 inches. I am assuming torque is in here somewhere? Then having a quick shufty at the specs for an industrial 100hp motor at 1000 rpm, it has more torque than my petrol engine. Torque is a word I know about, not what it is fully. So the basic ingredients get more complicated if you delve? More to this than meets the claim then. Get back to this later.

[nomuse]

Can I make a general plea to everyone to use the right units for mass and weight.
Every time you talk about weight in kg or mass in lbs you make a unicorn cry.

Aww.  And no-one has had to resort to slugs or poundels yet, even.

(I'm with you -- mks all the way.)

[gillianren]

I haven't used any!  Of course, this is because I'm refusing to have a conversation on any level deeper than "if you don't know the numbers, you don't know what you're talking about."  Also because, well, I don't know the numbers and can't have an intelligent discussion about the whole thing myself.  However, I at least know enough to know that, without the numbers, there is no intelligent discussion possible.

[ka9q]

In Zero G, an object with a mass of 1kg has a weight of 0kg
On the moon an object with a mass of 1kg has a weight of approx 167g because its a 0.167 G environment
On Mars an object with a mass of 1kg has a weight of approx 380g because its a 0.38G environment

<nitpick mode>
The kilogram is a unit of mass, not force -- even though many people abuse it for that purpose. A mass of 1 kg has an earth weight of 9.8 newtons, that being the proper unit to measure force, including the force of gravity on mass.
</nitpick mode>

So, your 1500kg LRV, while it only weighs 250kg on the moon, its mass remains 1500kg. However, that isn't the kicker. The power required to move it horizontally is unaffected by its weight; it affected only by its mass.

This isn't right. The power was greatly reduced by the lower lunar weight.

Although the energy (not power) needed to accelerate a given mass to a given velocity remains the same, in wheeled transport this is usually swamped by drag even when you don't recover kinetic energy through regenerative braking. (The LRV had non-rechargeable batteries.)

Earth vehicles have three main forms of drag: mechanical friction in the drive train, aerodynamic drag on the vehicle body, and rolling resistance in the tires. The aerodynamic drag force increases with the square of velocity while the rolling resistance and drive train frictional forces are independent of velocity once static friction is overcome (see Coulomb's law of friction). The power needed to overcome aerodynamic drag therefore increases with the cube of the velocity but only linearly with velocity for the other two forms. This causes aerodynamic drag to dominate total drag at high (e.g., freeway) speeds but to vanish at very low speeds (e.g., a golf cart).

Aerodynamic drag is of course completely absent on the moon. We don't know the friction in the LRV drive train, but with a motor in each wheel it's reasonable to assume it was small and in any event unaffected by gravity (though air pressure, or lack thereof, might have had a small effect). Rolling resistance was dominant, and since it is linear with weight (see Amonton's first law), on the moon it's only 1/6 of what it would be on earth with the same surface.

All this makes the energy losses of a vehicle on the moon much less than it would be on earth. On earth, the range per charge of my Nissan Leaf electric car is about 80 miles; on the moon, if paved roads were built it could be over 1,000 depending mainly on non-propulsive overhead loads.

So the Apollo LRV performed very well with only 1 hp of propulsive power.

[ka9q]

Weight is the effect produced by mass in a gravitational field.  Weight = mass times gravitation.

Actually, weight is the force produced by accelerating a mass (F=ma) and gravity is just one way to do it.  According to the equivalence principle of general relativity, the effect of the earth's surface pushing up against you as it resists gravity is completely indistinguishable from being accelerated by a rocket engine in deep space far from any gravitational field.

Similarly, you can experience weightlessness even in a strong gravitational field by free falling within it, e.g., in orbit.

[nomuse]

Maybe we should call it, instead of "weightlessness," something like "net forceless-ness relative to self inertial frame?"

Meanwhile, out in Apollo Denier land, there are still people whose understanding of lunar gravity is best summed up by the quote, "Heavy boots!"

[ka9q]

Maybe we should call it, instead of "weightlessness," something like "net forceless-ness relative to self inertial frame?"

What's wrong with 'free fall'?

[Nowhere Man]

Actually, weight is the force produced by accelerating a mass (F=ma) and gravity is just one way to do it.

I was trying to dumb it down for the OP.

Fred

[BazBear]

Someone else has probably said something like this by now, but I don't think we even need to address the numbers to discount the OP's assertion (I'm certainly not saying it's a waste of time, it's very educational to us more math challenged types, and the more thoroughly a claim such as this is debunked, the better). We have hours of footage of the rover moving, both from the rover and observing the rover, all taken in what would be an impossibly large movie set, in a vacuum no less. We are also to believe that the LRV wouldn't be rugged enough for a 1/6 g environment, yet would handle the 1g found on the impossible Earth film set with no problem.

[gillianren]

Someone else has probably said something like this by now, but I don't think we even need to address the numbers to discount the OP's assertion (I'm certainly not saying it's a waste of time, it's very educational to us more math challenged types, and the more thoroughly a claim such as this is debunked, the better). We have hours of footage of the rover moving, both from the rover and observing the rover, all taken in what would be an impossibly large movie set, in a vacuum no less. We are also to believe that the LRV wouldn't be rugged enough for a 1/6 g environment, yet would handle the 1g found on the impossible Earth film set with no problem.

All of this is true.  However, I do still firmly believe that, if the OP cannot provide the numbers to back up his assertion, it's proof he doesn't know what he's talking about.  I am so math-challenged that I don't get the numbers even when they're presented, and I acknowledge this.  However, that's also why I'd never make the assertion in the first place.  I know I don't know enough to make it.  I know the assertion is ridiculous on its face for several reasons, but if you can't present it in the right language, there's no reason to believe you know enough to know why it is ridiculous.  Even with the whole "impossible Earth film set" aspect thrown in.