[scientizscht (OP)]

If earth rotates why don't hanging items swing due to inertia?

[Bored chemist]

Why would they?

[scientizscht (OP)]

Because if you hang something and you move its base, it swings because of difference in inertia, air drag, etc.

[Kryptid]

The Earth rotates once per day. That's a very low revolution rate. At the equator, this results in a centrifugal force only about 0.34% of the force of gravity on an object at sea level: https://www.omnicalculator.com/physics/centrifugal-force

[alancalverd]

Look at a Foucault pendulum. It uses the conservation of angular momentum to demonstrate the rotation of the earth.

[evan_au]

(Oops! Overlap with Alan & Kryptid!)
It does!

The world's oceans swing out due to the Earth's rotation, by several kilometers.
See: https://en.wikipedia.org/wiki/Equatorial_bulge

The plane of a Foucault pendulum appears to swing around over 24 hours (but in reality the Earth rotates over 24 hours).
See: https://en.wikipedia.org/wiki/Foucault_pendulum

[scientizscht (OP)]

Can anyone explain the movement? Is there any video?

I see this but it is very confusing: https://en.m.wikipedia.org/wiki/File:Foucault-rotz.gif

[alancalverd]

Video of what? A swinging pendulum? Worth visiting a science museum or observatory to see a Foucault pendulum in action.

https://en.wikipedia.org/wiki/Foucault_pendulum goes through the maths in detail

[scientizscht (OP)]

So the plane of the pendulum movement rotates but I don't understand how this rotation relates to the rotation of the earth.

At a middle point in the north hemisphere like in London, the force exerted on the pendulum will be a constant direction force due to the rotation of the earth

How does this force translate into rotation of the pendulum plane?

[Bored chemist]

The simplest case is a pendulum at the north or south pole.
Imagine you pull the pendulum towards some particular star in the sky + then let it go.
It swings back and to, Moving in the same line towards and away from that star.

But the Earth rotates underneath it.
So, from the point of view of someone on earth, it looks like the plane of the pendulum rotates.

[Halc]

Because if you hang something and you move its base, it swings because of difference in inertia, air drag, etc.

The Earth is in free fall, and items hung from spinning things in free fall exhibit no tendency for any kind of back and forth swinging motion

[evan_au]

How does this force translate into rotation of the pendulum plane?

It doesn't.

The pendulum is hanging from a pivot, which doesn't exert any sideways force on the pendulum.
-  You start the pendulum swinging in a certain plane (eg lined up with the Sun).
- The pendulum keeps swinging in this plane.
- While the Earth rotates through 360 degrees.
- So from the view of someone standing on the ground, it looks like the plane of the pendulum has rotated through 360°.

...Just like the shadow on a sundial is lined up with the Sun. To someone looking at a sundial, it will appear as if the shadow has moved to different angles throughout the day.

[Petrochemicals]

Something i would have thought alan would have come up with (also used on ship)

 https://www.flightliteracy.com/gyro-precession/

It does indeed swing 360 in 24 hours

[Bored chemist]

If there was a mechanism that set pendula swinging just because they were on the rotating Earth, we would have a conservation law problem.
I can set up lots of them.
And, they will start to swing, but, in doing so they need to get energy from somewhere, and that has to be the rotational energy of the Earth.
But that swinging will be slowed down by friction and drag.
So eventually the drag will slow the pendulum down, but the Earth will keep them ticking until the Earth itself stops spinning.

But that can't happen- by the conservation of angular momentum.
You can't stop the Earth's rotation without having some external force acting on it.

[scientizscht (OP)]

Why the Foucault pendulum gets displaced but not a simply hanging item since the effect on the item is a constantly acting force with changing direction?

[Bored chemist]

Why the Foucault pendulum gets displaced but not a simply hanging item

Did you read my post?

[Kryptid]

Why the Foucault pendulum gets displaced but not a simply hanging item since the effect on the item is a constantly acting force with changing direction?

Most hanging items don't swing like pendulums.

[Bored chemist]

Why the Foucault pendulum gets displaced but not a simply hanging item since the effect on the item is a constantly acting force with changing direction?

Most hanging items don't swing like pendulums.

(cough) zero point energy (cough)

[alancalverd]

Most hanging items don't swing like pendulums.

Ipsi dixit. Swap Y-fronts for boxers.

[scientizscht (OP)]

I do not expect a hanging item to swing.

But if there is an inertial force due to the movement of earth on every item on earth, then I do expect a hanging item to be displaced under that force.

A simple experiment will show that if you have an item hanging from a hanging base and you move the base, the item will be displaced from its vertical position.

I expect the same to happen with any hanging item due to earth's movement, ie the rope should not be exactly perpendicular but rather at an angle from the perpendicular axis.

I expect during 24h, the hanging item and the rope to draw a cone with their movement (the base can be ellipse or circular or something like that).

Isn't this the case?