How could lower gravity give someone "the strength of ten men"?

Question

I've been thinking about how strong a human or humanoid would/could be on a planet with ten times lower gravity than Earth. After thinking about characters like John Carter of Mars, an Earth human that goes to a world with lower gravity and finds himself capable of giant leaps and can kill a martian with one blow, and conversely Superman, a humanoid whose species is adapted to a planet with higher gravity and is stronger on Earth where the gravity is weaker, I'm very curious as to the feats of strength and athleticism a human/humanoid could achieve.

Say we use the records set by Olympic athletes as the maximum average potential for a human/humanoid in Earth gravity - how does this change in lower gravity? Does ten times weaker gravity give someone "The Strength of Ten Men"?

Answer 1

Mass and Weight are Different.

In zero gravity a punching bag is weightless. Still, you cannot punch it into the ceiling with a fingertip. This is because the bag is too massive. Mass is a body's ability to resist movement and doesn't change with gravity.

In ZG if you prod the bag with your fingertip millions of times it will reach the ceiling. This is because the bag stays in place between pokes. This won't work in gravity because the bag resets after each poke.

In ZG if you poke the bag enough it will eventually hit the ceiling. That's because each poke gives the bag a sliiiiiight momentum that is not cancelled by gravity. So poke the bag one and wait a year for it to hit the ceiling. Or poke it a few million times and watch it fly!

Now replace the punching bag with a Martian on Mars. You won't send them flying unless they are stick-thin and have little mass.

Likewise, your jump speed will not increase on Mars. What changes is the max height of the jump? It might still take a while to reach the top of that skyscraper.

Probably your top speed is lower on Mars. Your legs have the same mass so each stride uses the same energy. So you could make the same number of strides per minute. Only now with lower gravity each stride pushes you higher into the air so you take longer to land. So fewer strides and less speed.

Your heart can pump the blood from your feet to your head more easily. This might change endurance. I'm not sure exactly. It might cause other problems too, like unnaturally high blood pressure

You're not stronger -- they're weaker.

The usual story is that evolving in low gravity, the Martians did indeed evolve to be much less massive. For example, they can get away with lighter, weaker bones, and less muscle.

Let's say Martians weigh about 30kg. About are half the mass of a grown human. Depending on their biology, your fist might go straight through a Martian's chest, or you might stagger them a few feet. This probably depends on where you hit them. Hit near the top bit of the Martian they will move back further as they try to catch themselves.

From a scientific point of view, I find a huge difference in strength hard to believe. The skeleton is only 15%ish percent of the body weight. Perhaps a smaller heart to pump blood up to the head, but most of the body is not there to resist gravity. Remember there are other stresses. Such as the stresses caused by the body on itself when turning suddenly.

Answer 2

Just want to add some data about swimming. From XKCD What If #24:

This(...) footnote contains some detail on the math behind a dolphin jump. Calculating the height a swimmer can jump out of the water requires taking several different things into account, but the bottom line is that a normal swimmer on the Moon could probably launch themselves a full meter out of the water, and Michael Phelps may well be able to manage 2 or 3.

The numbers get even more exciting when we introduce fins.

Swimmers wearing fins can go substantially faster than regular swimmers without them (although the fastest swimmer wearing flippers will still lose to a runner, even if the runner is also wearing flippers and jumping over hurdles).

Champion finswimmers can go almost 3.2 m/s wearing a monofin, which is fast enough for some pretty impressive jumps—even on Earth. Data on swimfin top speeds and thrusts suggest that on the Moon, a champion finswimmer could probably launch themselves as high as 4 or 5 meters into the air. In other words, on the Moon, you could conceivably do a high dive in reverse.

There is a link to this Youtube video in the original text, I recommend you see it. A man wearing a monofin manages to leap out out the water. For an instant he is practically vertical and only the fin touches the water. In lunar gravity even someone with little practice might be able to do this feat, and people who do have a lot of experience might do the 5 meters (~15 feet) jump mentioned in the XKCD article.

Answer 3

Relatively stronger

Gravity on a planet is incredibly important for the evolutionary paths. They determine if flight is possible and what kind, as well as how tall and strong creatures grow.

Differences most cited are:

• A planet with a higher gravity will have more stocky and less high animals.
• A low gravity one will be able to have taller, more slim animals.

This isn't fully true. The restrictions and likely outcome change. Slim animals would likely be crushed on a high gravity planet, but short stocky ones can live on a low gravity one (if things like deepsea sickness aren't afflicting them). They can evolve, although other designs are more likely to succeed. Heavy seeds that burrow on impact make sense in a high gravity situation, but are impractical in a low gravity one. Yet light seeds can be grown on a high gravity planet.

The reason your guy is likely stronger, is that creatures have grown in a way that doesn't waste energy they don't need. Not every creature is a bidy builder version for this reason. It wastes energy and time to get and maintain it, while it might be better not to eat everything around you just to keep those swoll legs.

Your guy lived on a higher gravity planet, so it required to get bigger muscles to do basic tasks. Thanks to the square cube law, he might actually be ten times stronger than the aliens, even if the gravity isn't ten times lower.

Jumping might not be one of them though. The bodies of the aliens might be better adapted and thanks to their build be able to go much further. Like a grasshopper can jump high and far in relative terms to humans. But the power behind the jump of your guy is stronger.

Answer 4

Gravity directly impacts weight.

Weight = mass * gravity acceleration

So, let's say an olympic weight lifter can lift up to 200kg which is

20 MASS * 10 gravity acceleration on earth = 200kg

The effect you would have is that on a planet with 10 times less gravity acceleration is that the weight lifter can now lift heavier objects

20 MASS * 1 gravity acceleration = 20kg ( mass won't change over planets but gravity will )

So, to lift the same weight as he could on Earth, he could lift 200kg as follows:

200 MASS * 1 gravity acceleration = 200kg

Conclusion:

He won't be stronger but he will be able to lift 10 times more mass than he could on Earth because of lesser gravity forces but still he's maximum weight lifting will be 200kg.

Answer 5

Unlike the other answers, I believe the OP is alluding to the body developing to be stronger under higher gravity than lower gravity. So it would be like you walking around all day with weights on so when you take them off you are stronger than everyone else whose body did not need to develop as much.

So the phrase shouldn't be "gives you the strength of ten men" as much as "gives you the strength of 10 martians". 10 times is too much though. Mars does not have 1/10th Earth's gravity. Mars has about half the graqvity.

Answer 6

In my opinion, the mass would decrease 10 times. The result is that your weight also decreases by ten, but the mass is the same, therefore it weighs the same and you do not have the strength of 10 men.