The discussion clarifies that there is no singular "force" that keeps the Earth spinning; rather, it is inertia that maintains its rotation. The Earth spins at a constant rate due to its angular momentum, while gravity plays a crucial role in holding the Earth together. The moon's gradual movement away from Earth is attributed to tidal forces, where the gravitational pull of the moon creates tidal bulges on Earth, leading to energy transfer that increases the moon's orbital distance. This complex interaction is influenced by the Earth's rotation and frictional forces.
PREREQUISITESAstronomers, physics students, educators, and anyone interested in understanding the dynamics of celestial mechanics and the Earth-Moon relationship.
Not if they spin at a constant angular velocity.quincy harman said:Spinning objects are accelerating
mfb said:There is no "force that keeps the Earth spinning" because the Earth spins at a constant rate (to a very good approximation).
Not if they spin at a constant angular velocity.
Points on the object are accelerating - but Earth is held together by gravity.
The tides induced by the moon slow down the rotation frequency a tiny bit, and they also move the moon outwards very slowly.
so it's a combination of centrifugal force and gravity? and if you're spinning at a constant speed but changing direction that is acceleration right?mfb said:There is no "force that keeps the Earth spinning" because the Earth spins at a constant rate (to a very good approximation).
Not if they spin at a constant angular velocity.
Points on the object are accelerating - but Earth is held together by gravity.
The tides induced by the moon slow down the rotation frequency a tiny bit, and they also move the moon outwards very slowly.
On the surface of Earth you feel both together, yes. Gravity is much stronger.quincy harman said:so it's a combination of centrifugal force and gravity?
That depends on what you mean with "acceleration". The individual parts of you are accelerating, but I would not say you as a whole are accelerating.quincy harman said:and if you're spinning at a constant speed but changing direction that is acceleration right?
Is the force that keeps the Earth spinning the same force that moves the moon farther away from us?
But it has it is constantly changing direction and it takes force to change direction and what is a tidal bulge is the Earth actually misshaped by the moon?CWatters said:An object on the surface of the Earth is moving at a constant speed and it's direction is changing so yes the object is accelerating. The force that causes it to accelerate is gravity. Without gravity the object would move in a straight line and fly off the Earth at a tangent to the surface.
There is no "force" that keeps the Earth spinning. It's inertia that keep it spinning.
The reason the moon is moving further away from us is quite complicated. The moon has gravity which causes a tidal bulge on earth. A combination of the Earth's rotation and friction means the tidal bulge isn't directly below the moon, but slightly ahead or leading the moon. The gravitational pull between the tidal bulge and the moon cause the moon to gain energy and move into a higher orbit. It's a bit like swinging a ball on a string around your head...by moving your hand around in a circle slightly ahead of the ball you can make it go faster.
quincy harman said:But it has it is constantly changing direction and it takes force to change direction..
and what is a tidal bulge is the Earth actually misshaped by the moon?
and how does gravity change the shape of Earth?CWatters said:Velocity has components speed and direction. In the context of the moon... Inertia ensures the speed stays constant. Gravity ensures the direction changes.
The most noticeable and significant effect are the water tides (many meters in height) but yes the solid surface of the Earth is also distorted (about 40cm)..
http://en.wikipedia.org/wiki/Earth_tide
It keeps Earth in the approximate shape of a sphere.quincy harman said:and how does gravity change the shape of Earth?
and how does gravity change the shape of Earth?
Because the gravitational field created by the Moon weakens with distance from the Moon, it exerts a slightly stronger than average force on the side of the Earth facing the Moon, and a slightly weaker force on the opposite side. The Moon thus tends to "stretch" the Earth slightly along the line connecting the two bodies.
I'm referring to the tidal bulges.mfb said:It keeps Earth in the approximate shape of a sphere.
sorry i didn't see thatCWatters said:
Thank you for the help.CWatters said:An object on the surface of the Earth is moving at a constant speed and it's direction is changing so yes the object is accelerating. The force that causes it to accelerate is gravity. Without gravity the object would move in a straight line and fly off the Earth at a tangent to the surface.
There is no "force" that keeps the Earth spinning. It's inertia that keep it spinning.
The reason the moon is moving further away from us is quite complicated. The moon has gravity which causes a tidal bulge on earth. A combination of the Earth's rotation and friction means the tidal bulge isn't directly below the moon, but slightly ahead or leading the moon. The gravitational pull between the tidal bulge and the moon cause the moon to gain energy and move into a higher orbit. It's a bit like swinging a ball on a string around your head...by moving your hand around in a circle slightly ahead of the ball you can make it go faster.