The Coriolis Force

force, which is itself mass times volume squared divided by the radius. Because the car is on the road, the net vertical force must equal zero. The vertical component is Normal force multiplied by the cosine of theta, which must also equal mass times the force of gravity. Combining these, we get these equations as seen in figure 26:

Figure 26.

THE CORIOLIS FORCE

There are fictitious forces that come into play when turning a corner in a car, riding in a spinning amusement park ride, and taking off in a jet airplane that everyone experiences. You feel, for example, that you are being forced backward on an airplane when you accelerate down the runway, which is not a force at all. It is instead the force of the seat pushing on you. When you make a tight curve in one direction, you feel like you are being forced in the other direction. In reality, you are going in a straight line but the car is moving in another curved direction. This arises from the use of the car as a frame of reference.

These fictitious forces come from using something as a frame of reference that is within a specific system. Passengers will use the car or airplane as the frame of reference, while in physics, the frame of reference is the earth. Using physics, only inertial frames of reference with real forces are used. The car is considered a non-inertial frame of

reference because it is accelerated to the side. The force that pulls you to the opposite direction of a turn is a fictitious force that has no physical origin.

Think of going around in a spinning ride at an amusement park, in which you feel pulled to the outside of the car you are riding in. You are in reality rotating together with the car but, in that non-inertial frame of reference, you feel a fictitious force called the centrifugal force that is trying to throw you off. The reason you must hang on is because you would otherwise go in a straight line.

This inertial effect, which carries you away from the center of rotation, is used in centrifuges. These will spin a sample rapidly in a circular motion, throwing the particles outward, which causes their sedimentation. The greater the angular velocity, the greater the centrifugal force. What really happens, though, is that the inertia of the particles carries them along a line tangent to the circle while the test tube in the centrifuge is being forced in a circular path by centripetal force.

This fictitious force or apparent outward force is described by Newton’s first law. This states that a body at rest will remain at rest, while a body in motion will stay in motion unless it is acted on by an external force. It is the inertia of a body with mass that will cause the object to continue in a straight line unless an outside force (centripetal force) acts upon the object spinning.

If a person throws a ball in a straight path while on a merry-go-round, it will go in a straight path and will no longer be directed along a circular path with respect to the earth. A person on the ground will see the ball going straight and will see the merry-goround circling beneath it. On the merry-go-round, on the other hand, the person will see a curvature of the ball’s path because of a fictitious force. This apparent curvature of the ball is called the Coriolis effect. It will curve in the opposite direction of the path of the circle rotating (clockwise or counterclockwise).

You should know that Earth is also an inertial frame of reference with the effect noted in things like weather systems. Because of this effect, weather systems rotate to the right in the northern hemisphere because the earth rotates counterclockwise as viewed from the north pole. It rotates in a clockwise direction as viewed from the south pole so weather rotates to the left. Wind patterns also observe the Coriolis effect. It causes