# The Earth now has 95% of its former gravity, what happens? **URL:** \ **Category:** Factual Questions\ **Created:** [June 8, 2011, 9:39pm UTC](https://boards.straightdope.com/t/the-earth-now-has-95-of-its-former-gravity-what-happens/584786 "2011-06-08T21:39:24Z")\ **Posts on this page:** 20\ **Page:** 3
**Author:** ![Darth\_Panda](https://avatars.discourse-cdn.com/v4/letter/d/ee7513/32.png) [@Darth\_Panda](https://boards.straightdope.com/u/Darth_Panda)\ **Post date:** [June 9, 2011, 8:21am UTC](https://boards.straightdope.com/t/the-earth-now-has-95-of-its-former-gravity-what-happens/584786/41 "2011-06-09T08:21:21Z")
I’m not an engineer, but I imagine that a lot of machinery is designed to take friction into account for rotating parts of the machinery (I’m thinking about turbines at nuclear and coal plants, for instance). With a change in gravity, it seems you would get different amounts of friction and then your plants would operate differently. We assume we kow how these things work (and we actually do most of the time, which is nice) - but when they start producing different power outputs than we expect them to, it could be hard to balance a system (generation versus load), leading to variations in power frequency (bad for electronic devices) or worse (brownouts, blackouts, plant damage, whatever). Again, this is a bit of a WAG. ---
**Author:** ![Candyman74](https://avatars.discourse-cdn.com/v4/letter/c/ad7895/32.png) [@Candyman74](https://boards.straightdope.com/u/Candyman74)\ **Post date:** [June 9, 2011, 8:25am UTC](https://boards.straightdope.com/t/the-earth-now-has-95-of-its-former-gravity-what-happens/584786/42 "2011-06-09T08:25:35Z")
> [@Alka\_Seltzer](#): > > No, you wouldn’t notice this, as you don’t accelerate anywhere when you are standing on the floor. Without additional information, it is impossible to distingush between acceleration and gravity. ---
**Author:** ![Alka\_Seltzer](https://avatars.discourse-cdn.com/v4/letter/a/c89c15/32.png) [@Alka\_Seltzer](https://boards.straightdope.com/u/Alka_Seltzer)\ **Post date:** [June 9, 2011, 8:52am UTC](https://boards.straightdope.com/t/the-earth-now-has-95-of-its-former-gravity-what-happens/584786/43 "2011-06-09T08:52:54Z")
> [@The\_Hamster\_King](#): > > It would feel exactly the same as being in an elevator accelerating down at about half the typical amount. Only it wouldn’t stop. With an elevator you get an initial dropping feeling that subsides as the elevator reaches maximum velocity. If the gravity of the Earth suddenly decreased by 5% you’d instantly feel the same faint dropping feeling, but it wouldn’t go away. (Until you adjusted to it psychologically, of course. But that might take minutes, hours, or even days.) Thinking about this some more, I think you are right. > [@Chronos](#): > > I still maintain that everyone would suddenly become very clumsy. Walking is basically a process of falling forward and moving your feet in front to catch yourself. Change the rate at which you fall, and your reflexes for when to move your feet where will be all wrong. This is not like putting on or taking off a heavy backpack; that doesn’t change the rate of falling. I’m sure it would be possible to walk without falling over, but it’s difficult to say how much effect a 5% drop would have without testing it. The nearest thing in my experience is walking along the length of a bus as it went over a rise, and that did make me quite clumsy. Has anyone ever tried walking along the aisle of an airplane while it was pitching down? What rate of pitch would give an apparent 5% drop in gravity? ---
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [June 9, 2011, 9:00am UTC](https://boards.straightdope.com/t/the-earth-now-has-95-of-its-former-gravity-what-happens/584786/44 "2011-06-09T09:00:12Z")
> [@Fear\_Itself](#): > > Yes, life exists at 5500 feet, but most of the oxygen in atmosphere is generated in the rain forest and other large green areas at much lower altitudes that do not thrive at that altitude. 1. Rainforests don’t generate any oxygen at all, they consume oxygen. 2. Most of the oxygen in atmosphere was generated in the oceans millions of years ago. We could remove every photosynthetic organism on Earth and have no noticeable effect on atmospheric oxygen levels for at least several centuries. 3. Rainforest grows quite happily at 10, 000 feet. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [June 9, 2011, 12:11pm UTC](https://boards.straightdope.com/t/the-earth-now-has-95-of-its-former-gravity-what-happens/584786/45 "2011-06-09T12:11:53Z")
reduced air density at any given altitude means reduced aerodynamic drag. Combined with reduced gravity, this means: -You’d get better fuel economy in your car; national oil consumption would go down. -You’d have less engine power available. -you’d have less traction, a bit like driving in the rain. Expect more accidents. Airplanes: -better fuel economy. -lower cruise altitudes (since the desired air density could then be found at lower altitudes) -future designs would enjoy even better fuel economy, since they could be made with smaller wings and fuel capacities, further reducing weight. When the gravity was reduced, the expansion of the atmosphere would result in adiabatic cooling. By my calcs, if the pressure drops to 95% of 14.7 psi, ambient temperature would drop from (for example) 70 to 62 degrees. This might make a mess of weather worldwide for a while. It’s unclear how fast the atmospheric expansion would happen; it depends on how fast the upper portions of the atmosphere rise, making room for the upward-moving mass of air below. The change in density would be commensurate, 95% of original. That means a lot of air would would want to leave enclosed spaces. If the density change happened rapidly, sports stadiums with air-supported roofs might be unable to vent fast enough. Lower atmospheric pressure means less dissolved gases in water. Aquatic life might suffer as a result. The timber line in mountainous areas would move to a lower elevation. ---
**Author:** ![Quercus](https://avatars.discourse-cdn.com/v4/letter/q/7ab992/32.png) [@Quercus](https://boards.straightdope.com/u/Quercus)\ **Post date:** [June 9, 2011, 12:48pm UTC](https://boards.straightdope.com/t/the-earth-now-has-95-of-its-former-gravity-what-happens/584786/46 "2011-06-09T12:48:30Z")
> [@The\_Hamster\_King](#): > > You’d feel it instantly in the pit of your stomach. A drop in gravity of 5% would feel just like standing in an elevator accelerating downward at about 1.5 ft/s^2. Most real-world elevators have accelerations in the range of 2 to 5 ft/s^2, so the feeling of the floor dropping out from under you would be definitely noticeable. Except I don’t feel a dropping sensation in most elevator rides, only the fastest ones. So with the reduction in gravity being less than your range for elevators, I don’t think I would notice it just standing. > [@Heracles](#): > > - Ships would run higher in the water, possibly causing a few collisions with low bridges. This is also an equation with gravity on both sides – the weight of the ship versus weight of the water it’s displacing. > [@MuleSkinner](#): > > Wouldn’t the effect be similar to someone that’s 100lbs. taking off 5lbs. of clothing and walking? Or losing 5lbs. of feces and fluids? Not quite. In standard 1-gee, A 95lb person and a 100lb person fall at the same rate. So they both walk at the same rhythm, just the lighter one uses a little less muscle force. But at 0.95-gee the person falls a little slower, so the timing changes, not just the amount of force. Don’t know if people would unconsciously adjust or not, but it’s at least plausible they wouldn’t. > [@Mangetout](#): > > In the longer run, the maximum sustainable size of arthropods may be slightly bigger. Your descendants may be pestered by larger cockroaches, for example. Given that there were huge arthropods in ancient (geologically speaking) times, isn’t the main limitation on arthropod size now thought to be breathing ability or competition/predation from vertebrates, not structural strength of the exoskeleton ? (Seriously asking, if anyone is an expert) ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [June 9, 2011, 1:32pm UTC](https://boards.straightdope.com/t/the-earth-now-has-95-of-its-former-gravity-what-happens/584786/47 "2011-06-09T13:32:39Z")
> [@Quercus](#): > > Except I don’t feel a dropping sensation in most elevator rides, only the fastest ones. So with the reduction in gravity being less than your range for elevators, I don’t think I would notice it just standing. The _speed_ of the elevator isn’t the issue; it’s the _acceleration_ of the elevator at the beginning and end of its journey. A very fast elevator may accelerate/decelerate very gently (but over a longer period of time), giving you a non-rollercoaster ride. On the other hand, an elevator with modest top speed may be designed for jackrabbit starts and stops that puts butterflies in your stomach during downward acceleration (when it starts going down or stops going up), and buckles your knees during upward acceleration (when it stops going down or starts going up). ---
**Author:** ![The\_Hamster\_King](https://avatars.discourse-cdn.com/v4/letter/t/8edcca/32.png) [@The\_Hamster\_King](https://boards.straightdope.com/u/The_Hamster_King)\ **Post date:** [June 9, 2011, 1:41pm UTC](https://boards.straightdope.com/t/the-earth-now-has-95-of-its-former-gravity-what-happens/584786/48 "2011-06-09T13:41:33Z")
> [@Quercus](#): > > Except I don’t feel a dropping sensation in most elevator rides, only the fastest ones. So with the reduction in gravity being less than your range for elevators, I don’t think I would notice it just standing. Faster elevators don’t have much higher acceleration, they just sustain it for longer so it’s more noticeable. A drop in gravity would feel like an elevator that accelerates forever. I think most people could acclimatize to it well enough in a few days to go about their daily business without constantly feeling wobbly and off-balance. But it would be quite a while before anyone could play most sports with any sort of skill. ---
**Author:** ![enipla](https://avatars.discourse-cdn.com/v4/letter/e/54ee81/32.png) [@enipla](https://boards.straightdope.com/u/enipla)\ **Post date:** [June 9, 2011, 1:49pm UTC](https://boards.straightdope.com/t/the-earth-now-has-95-of-its-former-gravity-what-happens/584786/49 "2011-06-09T13:49:26Z")
> [@MuleSkinner](#): > > Wouldn’t the effect be similar to someone that’s 100lbs. taking off 5lbs. of clothing and walking? Or losing 5lbs. of feces and fluids? I can walk just fine with a 40lb pack on, which also distributes your weight completely differently. 5% isn’t even going to be noticed. ---
**Author:** ![treis](https://avatars.discourse-cdn.com/v4/letter/t/bc79bd/32.png) [@treis](https://boards.straightdope.com/u/treis)\ **Post date:** [June 9, 2011, 3:51pm UTC](https://boards.straightdope.com/t/the-earth-now-has-95-of-its-former-gravity-what-happens/584786/50 "2011-06-09T15:51:01Z")
> [@Fear\_Itself](#): > > They trained hundreds of hours in simulators to prepare for it. Do you have a cite saying that they had difficulty walking, or were specifically training in how to walk? Any ideas on the apparent weight change while flying at 35000 feet? ---
**Author:** ![cmyk](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cmyk/32/3353_2.png) [@cmyk](https://boards.straightdope.com/u/cmyk)\ **Post date:** [June 9, 2011, 4:13pm UTC](https://boards.straightdope.com/t/the-earth-now-has-95-of-its-former-gravity-what-happens/584786/51 "2011-06-09T16:13:35Z")
Archimedes wouldn’t have to use as long a lever to move the world. ---
**Author:** ![Great\_Antibob](https://avatars.discourse-cdn.com/v4/letter/g/e47c2d/32.png) [@Great\_Antibob](https://boards.straightdope.com/u/Great_Antibob)\ **Post date:** [June 9, 2011, 4:15pm UTC](https://boards.straightdope.com/t/the-earth-now-has-95-of-its-former-gravity-what-happens/584786/52 "2011-06-09T16:15:04Z")
> [@treis](#): > > Do you have a cite saying that they had difficulty walking, or were specifically training in how to walk? Well, it goes almost without saying they were specifically [trained](http://www.bbc.co.uk/dna/h2g2/A1109882) for movement in their suits in a low-g environment. This is all well and good, but it ignores the fact that they were in bulky suits. It’s not like they’d be walking around like normal if they were on Earth in their spacesuits. So, how would this even apply to movement outside a spacesuit in Earth atmosphere but less than 1g? > [@treis](#): > > Any ideas on the apparent weight change while flying at 35000 feet? Nearly none. Your weight at 35000 ft altitude is almost exactly the same as ground level. It’s not a difficult calculation. At the top of Mount Everest (~29000 ft), you experience a weight decrease of less than half a percent. Outside the aircraft, you might get some additional apparent weight change from the decrease in air pressure, though. ---
**Author:** ![MikeS](https://avatars.discourse-cdn.com/v4/letter/m/919ad9/32.png) [@MikeS](https://boards.straightdope.com/u/MikeS)\ **Post date:** [June 9, 2011, 4:17pm UTC](https://boards.straightdope.com/t/the-earth-now-has-95-of-its-former-gravity-what-happens/584786/53 "2011-06-09T16:17:27Z")
> [@treis](#): > > Any ideas on the apparent weight change while flying at 35000 feet? You weigh about 0.3% less at 35,000 feet than you do at mean sea level. Note that the Earth’s asphericity and rotation make the “local” value of the gravitational acceleration _g_ vary by comparable amounts, so if you don’t feel a difference when at different latitudes, you shouldn’t feel a difference on an airplane. ---
**Author:** ![The\_Hamster\_King](https://avatars.discourse-cdn.com/v4/letter/t/8edcca/32.png) [@The\_Hamster\_King](https://boards.straightdope.com/u/The_Hamster_King)\ **Post date:** [June 9, 2011, 4:18pm UTC](https://boards.straightdope.com/t/the-earth-now-has-95-of-its-former-gravity-what-happens/584786/54 "2011-06-09T16:18:52Z")
> [@treis](#): > > Any ideas on the apparent weight change while flying at 35000 feet? According to my quick back of the envelope changes, gravitational attraction is only about 0.15% less at that altitude. That’s considerable smaller than a 5% drop. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [June 9, 2011, 4:20pm UTC](https://boards.straightdope.com/t/the-earth-now-has-95-of-its-former-gravity-what-happens/584786/55 "2011-06-09T16:20:45Z")
> [@](#): > > Chronos makes a good point here, although I wonder whether 5% would be within tolerance for us just to adapt behaviourally, rather than by evolution. Oh, no doubt we’d adapt, and probably sooner rather than later. It’d still be easily noticeable to everyone, right at the beginning, though. ---
**Author:** ![Asympotically\_fat](https://avatars.discourse-cdn.com/v4/letter/a/e47c2d/32.png) [@Asympotically\_fat](https://boards.straightdope.com/u/Asympotically_fat)\ **Post date:** [June 9, 2011, 5:02pm UTC](https://boards.straightdope.com/t/the-earth-now-has-95-of-its-former-gravity-what-happens/584786/56 "2011-06-09T17:02:12Z")
> [@The\_Hamster\_King](#): > > Faster elevators don’t have much higher acceleration, they just sustain it for longer so it’s more noticeable. A drop in gravity would feel like an elevator that accelerates forever. > > I think most people could acclimatize to it well enough in a few days to go about their daily business without constantly feeling wobbly and off-balance. But it would be quite a while before anyone could play most sports with any sort of skill. I disagree again, what you notice in the elvator is the jerk and the jonce (which ypu could argue would be felt in this situation). The actual effect of losing 5% of your weight would not be obviously noticeable. ---
**Author:** ![Quercus](https://avatars.discourse-cdn.com/v4/letter/q/7ab992/32.png) [@Quercus](https://boards.straightdope.com/u/Quercus)\ **Post date:** [June 9, 2011, 5:11pm UTC](https://boards.straightdope.com/t/the-earth-now-has-95-of-its-former-gravity-what-happens/584786/57 "2011-06-09T17:11:53Z")
> [@The\_Hamster\_King](#): > > Faster elevators don’t have much higher acceleration, they just sustain it for longer so it’s more noticeable. You didn’t post elevator speeds; you posted accelerations. I don’t know much about elevators so don’t know if they’re accurate, but the posted accelerations which are all higher than 0.05G. And since I do not usually notice a falling feeling from most elevators, I maintain that I, at least, would not notice a change from standing at 1-G to 0.95-G. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [June 9, 2011, 5:21pm UTC](https://boards.straightdope.com/t/the-earth-now-has-95-of-its-former-gravity-what-happens/584786/58 "2011-06-09T17:21:25Z")
> [@Quercus](#): > > Given that there were huge arthropods in ancient (geologically speaking) times, isn’t the main limitation on arthropod size now thought to be breathing ability or competition/predation from vertebrates, not structural strength of the exoskeleton ? (Seriously asking, if anyone is an expert) I think that actually supports my point. Arthropods were able to grow larger in the past because oxygen levels were higher. That’s an example of what becomes possible when a constraint is relaxed. It doesn’t matter if gravity isn’t the _main_ limitation because all of the constraints play a part together, not just the biggest one. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [June 9, 2011, 5:24pm UTC](https://boards.straightdope.com/t/the-earth-now-has-95-of-its-former-gravity-what-happens/584786/59 "2011-06-09T17:24:19Z")
> [@The\_Hamster\_King](#): > > According to my quick back of the envelope changes, gravitational attraction is only about 0.15% less at that altitude. That’s considerable smaller than a 5% drop. You also see an apparent change in gravity due to your flight path following the curvature of the earth. I posted the following in another thread elsewhere on this site: =========================================== It does. Disregarding local variations in the actual attractive force of gravity, a person standing on the equator (and therefore orbiting the center of the earth at 1041 MPH) would perceive a gravity to be 99.6% of what he felt standing at either pole. A person flying east along the equator on a 747 (ground speed 600 MPH) would experience 99.1% of what he felt at either pole. # The pilot of an SR-71 flying east along the equator (ground speed 2100 MPH) would experience 96.9% of what he felt at either pole; something dropped in the cockpit would accelerate toward the pilot’s feet only 96.9% as rapidly as would happen if the plane were parked at the north pole. ---
**Author:** ![Enilno](https://avatars.discourse-cdn.com/v4/letter/e/58f4c7/32.png) [@Enilno](https://boards.straightdope.com/u/Enilno)\ **Post date:** [June 9, 2011, 6:21pm UTC](https://boards.straightdope.com/t/the-earth-now-has-95-of-its-former-gravity-what-happens/584786/60 "2011-06-09T18:21:54Z")
> [@billfish678](#): > > If it happened very quickly pretty much everybody would be killed and most things destroyed as the surface of the earth sprung up many feet in a short period of time. I’ll let somebody else calculate how many feet/miles the spring up is. I’m not sure it’ll be quite so dramatic, but I figure there’s going to be a lot of earthquakes and volcanic activity as the surface of the Earth shifts to a new equilibrium. [Previous page](https://boards.straightdope.com/t/the-earth-now-has-95-of-its-former-gravity-what-happens/584786.md?page=2) [Next page](https://boards.straightdope.com/t/the-earth-now-has-95-of-its-former-gravity-what-happens/584786.md?page=4)