The Earth is rotating at speed 1600 km/hour, Why don't we feel it?

Have you ever think about it? or have you ever got a question like this? Honestly, I had a question like this from my friend when discussing the flat or round earth, and he asked this question as an argument that the earth is stationary and flat. well, we're not going to talk about a round or flat earth, but this question is quite interesting to answer. so let's deep into it.

Introduction

As one of the planets in the solar system, the earth rotates on its axis at a speed of about 1600 km/h or about 1000 miles/h. it is faster than the current fastest car, the SSC Tuatara which has a speed record of 508 km/h. in fact, it's slightly faster than the speed of the plane Airbus a380 which reaches around 1185 km/h. this rotation of the earth on its axis takes 24 hours and causes day and night to occur like what we have experienced so far.

Image credit: Wikiscient, Tdadamemd, Used under CC 3.0 license
Earth is the third planet from the Sun and the only astronomical object known to harbor life. About 29% of Earth's surface is land consisting of continents and islands. The remaining 71% is covered with water, mostly by oceans, seas, gulfs, and other salt water bodies, but also by lakes, rivers, and other fresh water, which together constitute the hydrosphere The Earth orbits the sun once every 365 days and rotates about its axis once every 24 hours. Day and night are due to the Earth rotating on its axis, not its orbiting around the sun

What do you think about when you see the illustration above? I'm sure you must imagine how we can remain calm and not feel the spinning of the giant ball with a speed of 1600 km/h which has been our residence.

So what makes us not feel the rotation of the earth?

The Reason why we don't feel the Earth is Moving

The first thing we need to know is the angular velocity and the linear velocity of the earth's rotation, these two velocity models will give us an idea of how the earth's velocity is on its axis.

Angular velocity is a vector quantity which states the angular frequency of an object and its axis of rotation.

We use the angular velocity formula to measure the earth's rotational speed based on its degree of movement over a unit of time.

v = r . ω
ω = v / r
Information :
v = linear velocity (km/h)
r = radius (km)
ω = angular velocity (rad/h)

ω = 1669,875(km/h) / 6.378,4 km
ω = 0.2618 rad/ h

1 radians = 57.32 0 , if converted into units of degrees which are more commonly known in angles then:
ω = 0.2618 rad/ h x (360 O / 2 π rad)
ω =15 ° / h
or equal to 0.0042 °/second

So guys, You can imagine how the angular velocity of the earth which is only moving to 15 ° in one hour, it's very slow. even if you are outside the earth's atmosphere you find it difficult to see the earth rotating.

It was even much slower than the angular rotation speed of Carousel.

Image credit Jim semonik From Pixabay
I'm sure you are familiar with the game, do you know how long it takes a Carousel to rotate 360 degrees? ok just say it 10 seconds only, then the carousel angular velocity is 36 degrees per second or 8600 times faster than the angular speed of the earth's rotation.

So how about speed of 1600 km / hour ?

Speed 1600 km/h is linear velocity But before we discuss why we don't feel this linear velocity, we need to know what linear velocity is and how to get its value.

Linear velocity is the relationship between the length of the linear path that the object travels per time interval. As we know that in the context of a straight line, velocity is defined as the change in displacement in a certain time. then in the context of circular motion, speed is defined as the length of the track covered in a certain time.

The formula for linear velocity (v) is the angular velocity (ω) times the radius (r). The radius used here is not the radius of the earth, but the radius of the earth multiplied by the cosine of the latitude of the location (Ө). In other words, r is the distance between points on the earth's surface and the straight line of the earth's diameter connecting the north and south poles. The average radius of the earth is 6371 km.

v = ω R earth cos Ө

Based on this formula, for people living on the equator (Ө = 0), the linear velocity is:

v = 0,000073 radian/second × 6371000 meters × cos(0)
= 465 meters per second = 1669,875->1670 km/h.

So within one hour, the earth rotates with a track length of more than 1600 km/h. but one thing we need to know is that the speed of 1600 km/h is the linear velocity of the point on the equator around the earth's diameter line connecting the north and south poles. so If the point on the surface of the earth gets closer to the pole (north or south), the linear velocity would get smaller as the value of cos Ө.

So, if it's said that the speed of the earth rotates always reaches 1600 or 1670 km/h, that's not true because that number only applies at the equator.

For example at 60 degrees latitude, the linear velocity drops to 835 km / h. Even right at the point of the north pole (90 degrees latitude), the linear velocity is zero because cos (90o) = 0.

So what makes us unable to feel the angular and the linear velocity of the earth's rotation ?

The answer is because we rotate along with the earth. for example when we board an Airbus A380 with a speed of 1185 km/h, and we could sit comfortably in the passenger seat. even though we are traveling at a very high speed, but we don't feel anything. this is because we move with the plane. so our speed is the same as the speed of the plane.

We can also take the example of the car. Visually, of course, we know that when we ride a car, our speed towards the ground is quite large when we see houses, trees and so on that are still on the ground. Houses, trees, and so on will appear to be away from us. A car moving away from the house (according to the observer at home) is the equivalent of a house moving away from the car (according to the observer in the car).

Likewise in the case of the earth's rotation whose linear velocity reaches more than 1600 km/h, but we don't feel it because the earth and all its contents (atmosphere, air, clouds, plants, animals and etc) also rotate.

Is there a chance to feel the rotation of the earth?

Yes, there is even though it means disaster, we can feel the earth's rotation if the earth stops rotating suddenly. if that happens then the consequences of Newton's first law of inertia principle will apply that an object will tend to maintain its previous state..

For example when you are in a car at a speed of 120 km/h and stopped suddenly. then according to the principle of inertia, we will tend to keep moving forward and our body is thrown forward at a speed of 120 km/h. that's why we use seat belts.

In the case of the earth's rotation, when the earth stops rotating suddenly, we and the objects on the surface of the earth will be thrown at a speed of 1600 km/h (depending on where you are). and also we will feel the impact of strong winds because as mentioned before, the air also rotates with the earth. Of course, it's not a good thing to feel the wind blows at a speed of 1600 km / h (for those on the equator)

Conclusion

As a giant ball floating in space, the angular velocity of the earth on its axis is actually very slow, we can imagine that the earth only moves 15 °/h it's even slower than the carousel rotation in general. however, it's fast enough for linear velocity for objects on the surface of the earth, especially humans. but we don't feel that speed because we rotate along with the earth.

References

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