0 Members and 1 Guest are viewing this topic.

Centrifugal force is not the same as gravity because there is no such thing as centrifugal force. It's an imaginary force. The only force in this context is centripetal force.

Quote from: Geezer on 18/03/2011 19:50:29Centrifugal force is not the same as gravity because there is no such thing as centrifugal force. It's an imaginary force. The only force in this context is centripetal force.That's what we've all been told by high school physics teachers with a BA in education, but it's not true. In fact, it's a question of frame of reference. In a rotating frame of reference, like Planet Earth, centrifugal force is real. We usually consider the weight/mass ratio measured by a spring scale or gravity pendulum to be the actual gravitational field strength. In the rotating reference frame of Earth, that is true; but in the sidereal reference frame centered on Earth, the spring scale is measuring the gravitational force (a vector pointing to the center of Earth) plus the centrifugal force (a vector point away from Earth's axis of rotation).

Centripetal Force is the force towards a center of rotation which could be gravity.

Centrifugal force is the force away from the center of rotation which is derived from changing the direction of momentum from a tangential to a curve.

If you tie a ball to a string and spin it around your head.The centrifugal force keeps it at a horzontal.

No, it is not the same as "real" gravity as it is not the attraction of masses towards a center.

If you were in a circular device in orbit that was 1 mile in diameter, spinning, you might not be able to tell the difference between artificial gravity and real gravity as long as you never looked out the window (perhaps you could have artificial stabilized windows).

Would you get dizzy?

As far as your bones.They wouldn't know the difference between gravity and artificial gravity.

Only if you're in a rotating frame of reference, like you're in a centrifuge or on a Merry-go-round or cornering in a car. Or the Earth's rotation is significant for what you're doing.

Also centrifugal force and coriolis force are actually pseudoforces; notably they don't obey Newton's third law!!!

Actually centrifugal forces aren't forces- you can't measure them (directly)!

If you're holding an accelerometer for example, on Earth, it says that it's being accelerated upwards, and it's the same in a rotating situation. It's measuring the force of the floor/chair holding you up against gravity, not the gravity itself.All parts of an accelerometer accelerate at almost exactly the same rate under gravity or centrifugal or coriolis, it can't really measure those accelerations at all.

That's not a centrifugal force, that's a normal force that follows Newton's third law.

QuoteCentrifugal force is the force away from the center of rotation which is derived from changing the direction of momentum from a tangential to a curve.Only if you're in a rotating frame of reference, like you're in a centrifuge or on a Merry-go-round or cornering in a car. Or the Earth's rotation is significant for what you're doing.

From the non rotating point of view (the non rotating reference frame) The 'force' that pushes you into the wall is your momentum; the wall 'slams into you' as your momentum tries to make you go in a straight line.

Incidentally, linear momentum doesn't convert into angular momentum, they're different things.

Normally most people talk about angular momentum in terms of rotation, but if I'm measuring angular momentum around my finger and a car drives past it 10ft away at 30 mph, in a perfectly straight line, then from the definition of angular momentum the car has (a constant) angular momentum around my finger,

Conversely, something that is rotating, each bit/atom/molecule that's moving has linear momentum as well as angular momentum, and you calculate the two completely separately- one can't turn into the other; they're just different, and independently conserved.

Actually, the approaching car's angular momentum is anything but constant relative to your finger. I think you will discover that the rate of change of angle increases and decreases according to the sine of the distance. On that basis there has to be an enormous change in the angular momentum of the approaching car, which, to me at least, sounds a teeny bit suspect.

Quote from: Geezer on 21/03/2011 03:49:32Actually, the approaching car's angular momentum is anything but constant relative to your finger. I think you will discover that the rate of change of angle increases and decreases according to the sine of the distance. On that basis there has to be an enormous change in the angular momentum of the approaching car, which, to me at least, sounds a teeny bit suspect. The angular velocity changes drastically, that's true, but unfortunately you've neglected the fact that the change in angular speed is compensated (precisely) by the change in distance, so it turns out that the angular momentum is exactly constant at all times; in fact it's simply distance at closest approach multiplied by speed.