Stolen (with permission) from @Moriarty.
What would be the effects if gravity on Earth was lessened by 10%…besides having to rewrite basketball rules and regs, of course?
Immediately the solar system would get messed up. Gravity would no longer be strong enough to keep planets in their current orbits so each planets would enter a more elliptical orbit with its current location as its perihelion. The sun would no longer be in equilibrium; gravity would no longer be able to hold the sun’s shape against the pressure exerted by its core fusion so it would expand.
I think we’d be in serious trouble.
How about instead just reduce the mass of the Earth by hollowing it out.
I think our atmosphere would thin out. How much? I am not sure but I doubt we’d be happy about it.
Also, for a while, you would have really strong people versus comparatively weak people born and raised in the lesser gravity. Sci-fi has used this. For example, in the TV show “The Expanse” a Belter (asteroid belt) is tortured on earth merely by making him deal with earth’s stronger gravity…the poor guy is simply unable to hold-up for days under the added strain he is unused to.
Please reread the first sentence of the OP.
If this happened instantaneously, a massive amount of stored energy would be released by both the crust and the oceans, resulting in massive seismic events and tsunamis. This would basically ‘frack’ the entire crust, likely releasing massive stores of underground natural gas and sequestered littoral methane stores that would dwarf even the massive amounts of anthropogenic releases we’re currently dumping into the atmosphere.
Longer term, you’ll see a lot of tectonic uplift, and a corresponding drop in mean sea level. We’d have to reassay mountain heights, and indeed the entire reference geoid would have to be redefined, which means that ballistic missiles and space launch rockets would not fly with good accuracy until that was done. At least this would lift up glaciers and at least temporarily reduce undercutting of grounded ice, although it would probably cause massive calving of Antarctic and Greenland ice shelves.
It would reduce pressure on foundations and footings, but would also screw up gravity structures like catenary bridges, so there would be a lot of reengineering and remediation required. Of course, all gravity-based measurements would change and would require conversions between weight and inertial mass for dynamic bodies. Breaking distances would increase and lateral skidpad values would reduce. You’d have to relearn how to lean a on motorcycle and throw a baseball. Climbing would be easier and gliding/parachuting would take longer. Plants would (likely) grow a bit taller but animals will remain about the same height with maybe a centimeter or two of increase for creatures with upright spines. Elephants still would not be able to jump, and no, people aren’t going to get significantly weaker or have longer lifespans.
“I’m starting to like the cut of this guy’s gibberish!”
Stranger
Define “significantly.”
As gravity goes down the people who live in that environment will be weaker than people living in a higher gravity environment. Granted there will be overlap. The weakest high gravity person will probably be weaker than the strongest low gravity person. It is a spectrum. Where do you draw the lines?
It seems to me that how the earth’s orbit is affected is an effect of gravity on earth. After all the gravitational force of attraction between the Sun and the Earth is equal in both directions. I’m not at all sure how you’re going to reduce the attraction of the earth on people, etc. and not reduce the attraction between the sun and the earth. Either the force of gravity is lessened or the mass of earth is lessened. In either case, I’m pretty sure the Earth’s orbit is materially affected.
If your method of reducing the gravity of earth is magic, then I don’t believe there is a factual answer.
I don’t think 10% weight reduction is going to significantly affect people’s strength. A person who weighs 180 pounds today will weigh 162 after the change. That level of change happens when people go on a serious weight reduction program, not exactly routinely but it’s not very rare. People don’t gain or lose significant strength when their weight changes by that much.
The mass of the Earth (which is about 1/333,000 of the mass of the Sun) is basically irrelevant in terms of its orbit. The only planet in the solar system that has any real influence on the Sun is Jupiter, and even then the barycenter is just barely outside the radius of the Sun. Of course, if the overall kinetic energy remained despite the mass change, the specific orbital energy (vis-viva) would have to increase in proportion, and that would definitely have the effect of changing the Earth’s semi-major axis.
Stranger
I think the odds are good that Earth would be rendered largely lifeless by the crust breaking up. The interior of the Earth is under massive compression forces by the planet’s mass; without that pressure the entire planet will expand. Not enormously with only 10% difference, but it wouldn’t take much to literally shatter the crust and create massive tectonic and volcanic activity.
does anyone have a definition of gravity for the layman
Why would the water level drop if the amount of water does not change? Ignoring ice melt and evaporation, which are not directly influenced by gravity, I believe, the water level stays the same.
The mountains will grow higher in a short geological timespan, but the sea will not become deeper.
This discussion reveals an ambiguity in the OP that should be clarified for a meaningful answer: Is it just that Earth’s gravity, and Earth’s alone, is reduced (by reducing the mass of the Earth by 10% but leaving all else equal)? Or is the gravitational constant (which determines gravitational attraction between all bodies) for the entire universe reduced by 10%?
I think the idea is that since the continents are floating on the mantle (due to being made of lighter rock), with lesser gravity they’ll rise up more.
The way I understood it the OP wrote
What would be the effects if gravity on Earth was lessened by 10%
meaning that the gravitational constant would be reduced by 10% on Earth alone and nowhere else. No idea how this is feasible, but that is how I interpreted it.
Yes, I agree the mountains will rise higher, but the water between them will remain just as deep as today, as it has nowhere else to go.
Walking will be easier on flat surfaces, but slopes will become steeper.
IMO it’s not a matter of oceans getting deeper. If the land rises up then from the POV of the land, the water level is lower. IOW: Stand on a beach. Magically elevate the beach 50 feet without wrecking anything else. Where is the waters edge now? A lot lower and a lot farther away than it was a minute ago.
Here’s another way to look at it …
If we remove enough mass that Earth’s surface gravity is 10% less, while magically preventing the voids created deep down below from collapsing, the remaining solid material of the whole planet will swell as the gravity pressure is reduced. So the lithosphere (dry land and seafloor) is now a larger diameter and therefore has a larger total surface area. The same amount of ocean water is now trying to cover a larger surface area. Which would have roughly the same effect as removing a corresponding fraction of seawater from the unchanged Earth v1.0 we live on right now.
Here’s a learned treatise on removing some seawater and what happens next: Drain the Oceans (xkcd.com).
What doesn’t happen when you go on a weight reduction program, is for all of the objects around you - your bike, your coffee cup, your lawnmower to suddenly weigh less than they did. A 10% reduction in gravity makes you lighter on your feet and makes your arms slightly stronger through not having to lift so much of their own weight, but it also buys you more lifting capacity against any object you want to pick up, because everything weighs less.
In yet other words: stand on a hut by the beach. Build a second floor on the hut. Has the water receded? No, it has not. The ground floor is still where it was.
We see tectonic uplifting here and there today: mostly in parts of the Earth that were under lots of ice not so long ago. The crust is rebounding. But if we reduce gravity by 10% we would see uplifting everywhere simultaneously: the sea does not change in depth.
It hardly will swell at all. Solids and liquids are imcompressible for all practical effects. I doubt Earth will swell by more than a dozen or two meters, if at all.
Are you tryng to make my point all of a sudden? Because all that I am claiming is that the water does not drain. It has nowhere to go. That xkcd cartoon is completely irrelevant here. You can make the mountains on dry land higher but the coastline in its totality, all over the world, will hardly move.