Interesting talk (commercial) on the force [not] of gravity.

YouTube

I enjoyed it.

@KellyJay

Thank you is there anything to talk about?

@Ponderable
Did you watch it, if so did you learn anything?
Do you need to be spoon-fed on what to say about it, if anything?
I found it interesting, if you didn't why post here?

@KellyJay said
@Ponderable
Did you watch it, if so did you learn anything?
Do you need to be spoon-fed on what to say about it, if anything?
I found it interesting, if you didn't why post here?

If, as she maintains, I am being accelerated upward while standing still on the surface of the Earth, why am I not launched into outer space? Don’t say because the air is holding me down. The air too must be being accelerated upwards, so what is keeping the air from being accelerated into outer space?

@moonbus said
If, as she maintains, I am being accelerated upward while standing still on the surface of the Earth, why am I not launched into outer space? Don’t say because the air is holding me down. The air too must be being accelerated upwards, so what is keeping the air from being accelerated into outer space?

@KellyJay said
Made me wonder why while standing on a globe we all can be pushed down if we are on opposite sides of the earth?

@moonbus said
Makes me wonder why, when I stand on a bathroom scale, it reads 70 kgs, when Ms Physics says I’m accelerating upwards. If I’m accelerating upwards, the scale should be too, so it should read zero kgs. There is something seriously missing from her explanation.

@KellyJay said
I am it’s all relative? 😉

@moonbus
Well the reason you don't fly into the air MIGHT have something to do with the 9.8 meters per second per second of acceleration you WOULD feel if you were not on solid ground.
The centriptal force V centrifugal force is very weak compared to the curved path we all feel in space time by the mass of the Earth.

It turns out the force flinging us into space would have to be about 17 times stronger than it is now to overcome gravity to do that. So the 'force' of gravity, really just a space time curve caused by the mass of Earth, is about 9.8 M/second squared and the force slinging us into space is abut 0.5 M/second squared, WAY too weak. If Earth spun around not once in about 24 hours but about an hour and a half the force could fling you into space but even then the atmosphere would slow you down and once you leave the surface of Earth you would probably not make it to space because of atmospheric drag because the slinging force would be gone and it would only be the inertia that would keep you going up but gravity would immediately start working to slow you down so if the force of gravity holding you to the ground was about as equal to centrifugal force slinging you up, the centrifugal force stops as soon as you let go of the ground and would continue only as much as the inertia lets you go and gravity would stop you from accelerating any further and the only force left would be your own inirtia.

@sonhouse
Like if you are riding a skateboard down hill on a road, you certainly are gaining momentum but you are not accelerating which an accelerometer would tell you.
Newton would say you ARE feeling the force of gravity but if you say, are in space like where ISS is, and you hang out in your space suit outside ISS, you won't accelerate, an accelerometer would show zero acceleration. So suppose you suddenly are doing zero meters per second while you are 250 miles high, you will fall towards earth but the accelerometer is still not showing any acceleration because you are just falling into a space time region that will pull you towards the center of mass. Now if you have a nice retro rocket on your space suit and you somehow survive crashing through the atmosphere at a really high rate of speed, then when you start the rocket motor shooting stuff away from your feet which would be pointed down and your head up you will be accelerated, the accelerometer will read that acceleration but you are then countering the space time curve which began giving you a change in momentum because you are in fact falling towards Earth and slowing down by the rocket.
So the rocket works well, you are falling but the rocket is doing say 1 g of actual force trying to get you to go in the opposite direction that you are falling into, so you do feel that. And when you finally land on solid ground and the rocket stops shooting crap out the ass end, you are STILL feeling an acceleration and the accelerometer is in fact reading you are accelerating but you now have zero relative momentum and all you are now feeling is the space time curve of Earth and it is the outward pressure of the mass keeping everyone from forming a black hole, albeit a tiny one, EARTH would be about 3 mm across if it was all of a sudden not able to withstand the spacetime curve of the mass of Earth and going downwards towards the center of Earth and a tiny black hole is born.
But the tension of matter keeps that from happing and till you stop moving relative to the fall you would be in you are gaining kinetic energy but not accelerating even though you are going faster and faster. Then if you say are also squished down to a micron size you hit the black hole horizon and say if you still have that rocket you could slow down which the accelerometer WOULD show a reading of the force exerted by the rocket but as soon as said rocket shuts off, your change in velocity ceases but when you land on the surface of the now tiny black hole the accelerometer still shows pretty much the same reading and you feel the same weight on the surface of the black hole, assuming you had a platform to stand on down there, you would not feel any different from the time you were on the rocket because you are still experiencing acceleration in spite of not getting any more change of velocity because now you are now experiencing the acceleration of space time needed to hold you still. And your accelerometer would still be thinking you are accelerating in space but you are not changing your relative position, no relative velocity change.

@sonhouse
You know, there are plans afoot to use that effect to gain energy by having a system that shoots mass off the moon with a solar powered rail car that shoots it off, because there is no atmosphere, there is no atmospheric drag so a real acceleration can be done forever on the moon if you have the energy so it can be built, not out of the reach of physics, to accelerate a mass off the surface of the moon by say a magnetic levitation so there is very little drag, so velocity can build up quickly and it flies off the moon and if it is done at the right velocity and angle and such, that mass will exceed the escape velocity of the moon with is about 2.4 Km/second, 5400 miles per hour, a LOT lower than Earth so a lot less energy would be expended on the moon to get say 100Kg off the moon and flying towards Earth.
Now if you do it right, right velocity, right angles and the like then it floats with no more rocket force needed, and the space time curvature of Earth will add velocity to that mass and when it gets in the vicinity of Earth it will be going something like 40,000 km/hour, about 7 miles per second. That represents a massive increase in that 100Kg kinetic energy gotten basically for free, not quite but close enough for this argument.
So a satellite is up in orbit and its orbit is designed to capture that mass and slow it down to zero in the length of the probe, whatever, say a km long.
Now it wants to slow down that mass to zero and so you use a linear magnetic accelerator in reverse like manually spinning a motor which generates a current based on the energy used to spin the motor which is now a generator. It matters little if the energy is spent in a straight line or a curved one, the linear motor runs in reverse and generates a LOT of energy for free basically, and using that energy to store up for subsequent shoots from the moon, in this example 100 Km at a time and a continuous catch and kill velocity trick, generating a huge amount of energy that can be stored in many ways on board the craft, spinning rotors, charging lithium ion batteries, supercapacitors, whatever, then using the energy stored that way to beam microwave energy beams to Earth and Earth thus getting may gigawatt hours of basically free energy of course minus the energy and money it took to make the magnetic sling on the moon and the satellite in orbit to catch and kill the kinetic energy gained falling from the moon to Earth.
Pretty fancy scheme and it could work in real life if there was the will to implement such a system. The mass collected could be used to expand the catcher satellite or whatever they wanted to use that mass for.
This was a science article in Analog sci fi magazine from decades ago but I always remembered that ingenious way to get basically free energy not using solar cells.

@sonhouse

Thanks for your detailed reply. What is counterintuitive to the layman is this: if a person is standing still on the surface of the Earth, how can he be accelerating? What is the accelerometer registering, if the person is not moving (with respect to the surface of the Earth)? Is it registering the motion of the planet (on its axis and orbiting the sun)? And if so, why does the accelerometer show the direction as up (away from the centre of the planet) and not a spiral (direction of orbit and rotation combined)?

@moonbus said
@sonhouse

Thanks for your detailed reply. What is counterintuitive to the layman is this: if a person is standing still on the surface of the Earth, how can he be accelerating? What is the accelerometer registering, if the person is not moving (with respect to the surface of the Earth)? Is it registering the motion of the planet (on its axis and orbiting the sun)? And if ...[text shortened]... up (away from the centre of the planet) and not a spiral (direction of orbit and rotation combined)?

@moonbus
Like the spring in the video, it will be compressed when your elevator is on the surface of Earth and you can't see out the elevator to know you are in fact on the surface of Earth.
The equivalency principle of Einstein says you can't tell say you are in an elevator in space but accelerated by the rocket, you and the spring feel being stuck to the floor whether you are stuck on the surface of Earth or a billion miles out in space accelerating at one g.

So if that elevator is in space, and there is a rocket shooting out the bottom, and it is accelerating at 1 g, if you weighed 200 pounds on the surface of the Earth and you had a scale with you, it would show you weigh 200 pounds and the spring would show compression if it is upright on the floor, It is acceleration in both cases even though you see yourself not moving. So if you are say a couple hundred miles up in your elevator and you don a spacesuit and jump out of the elevator which has a rocket shooting it up and away, you would be floating in space but depending on your velocity relative to the surface of Earth, you could be being pulled back down to Earth but in this case you are accelerating just by following the curvature of space but you don't FEEL acceleration, if you didn't see Earth, say you have your body turned away from Earth looking at the moon or stars, you wouldn't even know you were moving because you feel nothing.
That is the gist of Einstein, the acceleration you don't feel is just falling down a gravity well, the curve of spacetime you happen to be caught up in.

The fact you are in that spacetime curve means if you happen to have an atomic clock with you, it would be running a bit slower than if you were say 10 billion miles out in space away from planetary mass and most of the gravity well of the sun and the clock would be running a tad bit faster. It runs slower the bigger the gravity well you are in and there are two effects going on here, the fact you are just present in a gravity well, say 200 miles high, you get effect #1 from just being in that spacetime curvature due to the mass of Earth but effect# 2 is another change in time flow because of your velocity, how close you are to going the speed of light, it slows down just by velocity also so you get a double whammy and the clock will start changing all the way down to Earth.

Atomic clocks now are so accurate they can sense the change in time flow by just moving the clock up a meter or down a meter, it will show changes because time flow is different in different distances from the center of mass, in this case Earth's center of mass.