# Tag Info

31

Because the rotation of the earth is very smooth and doesn't change, the centripetal acceleration we feel is very nearly constant. This means that the (small) centrifugal force from the rotation gets added to gravity to make up the "background force" we don't notice. Earthquakes are not at all smooth and the accelerations involved are large and change ...

21

Dan's answer is essentially good, but miss one effect : the Coriolis effect. You can imagine a planet spinning much more rapidly than the earth, but at a constant angular speed. On that quickly rotating planet, the explanation of Dan would still stand, but as soon as on moves, we would feel a lateral Coriolis force. The Coriolis acceleration is ...

10

The whirl is due to the net angular momentum the water has before it starts draining, which is pretty much random. If the circulation were due to Coriolis forces, the water would always drain in the same direction, but I did the experiment with my sink just now and observed the water to spin different directions on different trials. The Coriolis force is ...

9

Ok, here is my (hopefully rigorous) demonstration of the origin of these forces here, from first principles. I've tried to be pretty clear what's happening with the maths. Bear with me, it's a bit lengthy! Angular velocity vector Let us start with the principal equation defining angular velocity in three dimensions, \dot{\vec{r}} = \vec{\omega} \times ...

7

Yes, the ball would land in front of you. If you watch from outside the space station, the ball moves in a straight line at constant speed while you move in a circle at constant speed. That means the distance the ball takes to get from point A (where you release it) to point B (where it hits the floor) is shorter than the distance you take. Further, ...

5

The calculation of the Coriolis force is dependent on latitude: $F = m a$ where $a = 2 \Omega sin(lat)$, with $\Omega$ being the Earth's angular velocity $m$ is the mass of the object in question The Earth's angular velocity is (about) $7.29 \times 10^{-5}$ rad/sec So, for a sink with a couple gallons of water in it at 45 degrees north... the Coriolis ...

5

Of course that there would be forces that would try to bend the track but they would be tiny. Each segment of the track would be under the action of $-2m \Omega \times v$ Coriolis force. Note that the Coriolis force only depends on velocities, not accelerations as you stated! In other words, there is the Coriolis acceleration, $-2\Omega\times v$, and you ...

4

Since you want to explain it to your daughter, take a plastic bottle, cut the bottom open, turn it upside town, hold the top closed and fill it with water. Give her that bottle and have her release the top (which is on the bottom now, sorry for the bad phrasing). The water will whirl in different orientations whenever you repeat this (if it whirls at all) ...

3

The whirl happens in the draining tube, whose optimal solution to drain the bathtub is a laminar flow allowing for some rotation in the tube. What you see in the surface is the match between the solution of flow in the tube and the solution of flow in the surface. Angular momentum of the flow gets modified a lot as the tube twists and twists, sometimes even ...

3

It does have an effect. Also see this paper about modelling tsunami propagation. As noted in the paper, the Coriolis force only becomes important over large distances. Here's an article on MathWorld including many references.

2

The Coriolis effect is proportional to velocity: $\boldsymbol{ F}_C = -2 \, m \, \boldsymbol{\Omega \times v}$, where $\boldsymbol{\Omega}$ is the angular velocity (of the earth). As waves, tsunamis have very high velocities, you would think it would be enough to see the Coriolis effect, but in fact there is little effect. When in deep water, tsunamis move ...

2

Your adjective "large" in "large whirlpool" may be very misleading. If you mean hundreds of meters, no effect of the Coriolis force may be visible by a naked eye at this scale. The origin of the whirlpool had to be different. Quite generally, tsunami is all about waves, and if one has a wave, molecules of water are moving back and forth, in circular ...

2

It does. To convince yourself, remember that rising hot air does experience a Coriolis force, so I am quite sure that your bubble does too. Also, think of what the Coriolis acceleration is - it is an apparent acceleration due to the fact that you, the observer, are in a rotating reference frame, so your definition of "straight up" is actually a curve. When ...

2

You can think about it like this: It takes one day for the earth to perform a full rotation (about 86k seconds), on the other hand, it takes a few seconds for your sink to drain (lets say 10 seconds). So it takes 8600 times longer for the earth to do a full rotation than it takes the water to drain down the sink. It is not too hard to imagine that the ...

2

Sure coriolis force applies, but I think a much simpler intuitive explanation is conservation of angular momentum. Think of the spinning skater who pulls in his/her arms & legs, spinning faster. If you look down on the earth from the north star, you see a whole hemisphere covered with air rotating counterclockwise. At the pole, it's basically not ...

1

There is no significant difference between what happens in the east-west direction and what happens in the north-south one. Upon impact it will experience a pretty sudden acceleration due to the impact, and depending on the trajectory and the nature of where it hits the ground, it may not stick, but rebound, skid, or whatever...

1

The Coriolis "force" isn't a proper force. It's probably better called the Coriolis effect. It's named after a French mathematician and engineer. In a rotating frame of reference, like the earth's, when we differentiate a dynamical variable (like the position of an object -- here, Baumgartner) with respect to time we get two terms. The first is just the ...

1

You land slightly ahead of where you jumped. As mentioned in the comments, see here. The Coriolis effect only applies to things that are moving in the rotating reference frame. If the air is stationary in the rotating frame, it feels only the centrifugal force. There will be a pressure gradient, creating buoyancy, just like on Earth, but all the air will ...

1

A discussion by 'The Straight Dope' website http://www.straightdope.com/columns/read/149/do-bathtubs-drain-counterclockwise-in-the-northern-hemisphere references experimental work carried out but Ascher Schapiro in 1962, which concluded something like it all depends on the shape of container and how its stirred before being left to empty. Here is ...

1

The main effect is angular momentum (rotational inertia) in the water set up by various movements before you start observing, such as getting out of your bath. This results in the water level being lower near the centre of rotation than further away, setting up centripital forces which maintain the rotation. When the difference in levels is significant ...

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