Chapter 23 Why Carrying Big Rocks Can Be Faster, Physical Explanation

Seeing that many friends are puzzled about why it is faster to carry a heavy stone in Chapter 21, and even laugh at Zhaizhu's common sense of physics, Zhaizhu feels the need to explain.

Many people know about Galileo's Leaning Tower experiment. Two iron balls, one big and one small, fell from the leaning tower at the same time and landed on the ground at the same time. air buoyancy.

Air buoyancy is very small, but it also affects larger objects. In addition, the biggest influence on the acceleration of gravity is air resistance, wind resistance.

When a person falls from a high altitude, encountering wind resistance will offset the acceleration, allowing the falling speed to reach a fixed value. This fixed value is 25 meters to 50 meters per second, and this speed cannot be exceeded.

The density of stone is seven times that of the human body, the potential energy is greater, and the effect of wind resistance is smaller, so the speed can be faster.

So, is Galileo's Leaning Tower experiment correct? Which one of the two iron balls, one big and one small, will fall faster at the same height?

Let's use junior high school physics to calculate.

Two round stones, one big and one small, air resistance Fw=1/16·A·Cw·v^2 Suppose CW=1, A1=1, A2=r^2, mass m1=1, m=r^3. r>1, air resistance FW1=1/16*V1^2FW2=1/16*V2^2*r^2

Gravity: G1=g, G2=r^3*g

1. If the speed is the same, the acceleration a1=(g－1/16*v^2), a2=(r^3*g－1/16*v^2*r^2)/r^3=( g－1/16*v^2*1/r)>a1a2>a1, the big rock accelerates fast.

2. When the limit speed is reached, the speed does not increase. Then 1/16*v1^2=g, 1/16*v2^2*r^2=r^3*g, 1/16*v2^2=r*g, V2>V1, the big iron ball moves at a constant speed The terminal velocity is high. So the big iron ball hits the ground first.

3. It is more difficult to calculate in the case of air buoyancy, but there is an easy way to test it, in water. Water also has buoyancy, take an iron ball and a piece of meat, fall into the water, and see who lands first. Obviously the iron ball landed first.

You can also use a similar experiment, that is, an ant and an ant lying on a stone fall from the air at the same height at the same time, which one will land first?

If you still have doubts about this, go to junior high school physics, do more calculations, and don't take it for granted.