Category: "everyday physics"

Does "centrifugal force" exist?

October 18th, 2016
Does "centrifugal force" exist?

There are two kinds of force, which are the real force and the fictitious force. In fact, the centrifugal force is NOT a real force, but a fictitious force.

Now you want to say, "When you drive a car during a curve, you actually feel a force outward direction! Isn’t it real?" In fact, this is a force emerged relatively to the centripetal force when turning a curve. Of course, if you stop tracking the curve, you will not feel the “centrifugal force.”

Conversely, if the centrifugal force is really exerting an object or a car, then it moves to the outside of the direction. However, it does not happen in any case.

For instance, as shown in the figure, there is a ball with a certain mass connected to the string. Then, rotate it around the center to make a constant velocity of circular motion. If the centrifugal force is real, the ball jumps out on the outside of the circular orbit when released at B.

But the reality depicts as jumping toward tangential direction as shown in the figure on the right. This is because the centrifugal force is not a real force.

This is the same for a car driving in a curve. When the car goes too fast to turn the curve, the car skids off toward the tangential direction of the curve although we always feel like the car goes off toward perpendicular to the curve’s orbit.

In general, there is another fictitious force other than centrifugal force with a moving object on the Earth. The object looks turning for the outside observer; namely, there appears to be a fictitious force, which is known as the Coriolis force.

As you can see, it does not happen unless the Earth is spinning. Due to the Coriolis force, the hurricanes on the northern hemisphere rotate counter-clockwise.

We can say that the fictitious force is a force generated associated with the correspondent real force or the motion of the reference frame. It is not a force that exists independently.

Physics Question and Answer: What is light?

July 25th, 2016
Physics Question and Answer: What is light?


How do you explain the nature of light from physics point of view? Why do the Sun and the Moon appear to be the same in size to us when you look at them from the Earth? Is it just an accident?


When you see it in a large scale, light is an electromagnetic wave, it travels through space as a transverse wave. So called white light looks white to naked human eyes because it contains all wavelengths of seven colors of a rainbow. We can only perceive colors in spite of the fact that there are various electromagnetic waves in the world. In fact, we are surrounded by invisible light that technology has made us able to use in everyday life. For example, remote-control, radio wave, mobile phone, etc. In a smaller scale, light acts as gathered particles. There is a machine with attached feathers that was designed to turn when light shines the feather. The machine is called the radiometer. In a much smaller scale, it has been known in physics to determine the energy of light, which is not based on the intensity of light; rather, it is determined by its wavelength. 

Also, the way the Sun and the Moon appear to be the same in size to us. Scientifically, we can only say that it is an accident; however, we can not exclude some unknown reason behind it. It is interesting to see that the Earth is the only planet within our solar system that has a satellite as big as the Moon. And if you'd notice, the Moon turns once in its axis while it revolves around the Earth in a month so that showing only the same surface towards the Earth at all time making other side hidden to see from the Earth.

If the distance between the Sun and the Earth had been slightly different, neither of human life nor any form of life on Earth could not have happened. 


Yasuo Koide & Hiro Shimoyama

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