Hello, I was watching a video today on what will happen in the future like The Milky way colliding with Andromeda. What was also said was that the moon moves away from earth 1cm every year. I was talking to a friend about it and he was adamant that this isn t true as he said "Gravity on earth would change...
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answers:
YKhan say: The laws of gravity don't change, but the force of gravity changes all of the time, depending on mass and distance, as Newton's Laws demonstrate. The force of gravity goes down, the further away you are from from an object, in fact it goes down according to an inverse square law, if you're twice as far away, then the force of gravity is 4 times as weak.
So yes, as the Moon recedes, it's force of gravity to objects on Earth goes down. The most obvious object affected by the Moon are Earth's tides. The water is actually lifted slightly by the Moon's pull. As the Moon's pull goes down, the tides aren't lifted as much.
So yes, the balance of gravitational forces do change every year on Earth due to the receding Moon. However, it's unnoticeable. In fact, far more significant than the Moon's recession from Earth is it's orbit around the Earth, where parts of the Earth directly underneath the Moon are being pulled at different rates vs. parts not directly underneath. But even this more significant gravitational change is barely noticeable by us on Earth.
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spot a say: The moon moves away at 1.496 inches or 38mm per year
Gravity does indeed change every year because of this
You can calculate the change in the gravitational pull of the moon on your body using the formula G * m1 * m2 / r1^2 - G * m1 * m2 / r2^2
where
G = 6.67408 × 10^(-11) m3 kg-1 s-2
m1 = mass of moon = 7.34767309 × 1022
m2 = your mass = maybe 60 kg
r1 = (384,400 - 6871.001) km Assuming you are about 2 m tall