"Long Wu weighs only 110 kilograms, he can push a 25,000-kilogram truck, but he can't push Chen Xiaowang, who weighs 93 kilograms. 》
1. When standing upright, what is the maximum static friction between Long Wu, Chen Xiaowang and the ground?
The maximum static friction is calculated as follows
f=μn=μg
If the coefficient of static friction is μ = 0.2, then
The maximum static friction between Longwu and the ground is
0.2× 110 kg force = 22 kg force
The maximum static friction between Chen Xiaowang and the ground is
0.2×93 kgf = 18.6kgf
2. Is the maximum static friction between a 25,000 kg truck and the ground 5 tons of force (that is, 5,000 kg force)?
At that time, an expert said that the thrust required to propel a 25-ton truck must be greater than 5 tons of force. His basis is
If the coefficient of static friction between the truck and the ground is 0.2, then
The maximum static friction between a 25-ton truck and the ground is
0.2× 25 tons of force = 5 tons of force = 5000 kg of force
Only when Longwu's horizontal thrust is greater than the maximum static friction between the truck and the ground is 5 tons of force (that is, 5000 kg force), can the 25-ton truck be propelled. So the expert believed that Long Wu had at least 5 tons of force (that is, 5,000 kilograms of force) to propel the truck at that time.
The maximum static friction between Longwu and the ground is only 22 kg force, it is impossible to produce a horizontal thrust of 5 tons of force (that is, 5000 kg force) on the truck, when the horizontal thrust of Long Wu push is greater than 22 kg force, Long Wu slipped under his feet. It is impossible for Long Wu to push a truck with horizontal force. It can be seen that the expert's analysis is wrong!
Why do experts make the wrong analysis? He mistook the rolling friction between the truck and the ground as sliding friction. Trucks have wheels with rolling bearings with very little coefficient of friction and very small. The rolling friction between the truck and the ground is minimal, with a rough calculation of only about 50 kg of force. Long Wu was still unable to propel the truck with a horizontal force of 22 kilograms. The average person can't push it.
3. Why can Longwu push the truck?
When Longwu pushes the truck, the body tilts forward, and when the foot pedals to the ground, the force of the foot on the ground slopes backwards and downwards, which can increase the maximum static friction between Longwu and the ground, at this time, the reaction force of the ground facing Longwu's feet is obliquely upwards, and the rear wall of the truck carriage produces an oblique downward force on the palm of Longwu, and the palm produces an oblique upward force on the rear wall of the truck carriage, so that the maximum static friction between the truck and the ground is reduced. In this way, the maximum static friction between Longwu and the ground increases to be large enough, and the maximum static friction between the truck and the ground is reduced to small enough that Longwu can push the truck without slipping backwards under his feet.
It has been calculated that to push the truck, Long Wu's body needs to be tilted forward at an angle of about 50 degrees, and the size of the oblique upward thrust is about 76 kg force.
4. Why can't Long Wu push Chen Xiaowang?
When Long Wu and Chen Xiaowang pushed hands, Chen Xiaowang took the following measures:
(1) Chen Xiaowang stands with a big lunge before and after to increase his balance stability coefficient and improve his balance stability.
(2) Chen Xiaowang did not let Long Wu push according to the position to stabilize, so that Long Wu could not stabilize and continue to exert a gradually increasing force on Chen Xiaowang.
(3) Try to make Longwu act on Chen Xiaowang's force pointing forward and below, even if the force pointing of Longwu acts on himself is forward and above, so as to reduce the maximum static friction under Longwu's feet and increase the maximum static friction under his feet.
Therefore, although Long Wu weighed more than Chen Xiaowang, his body was stronger than Chen Xiaowang's, and he had more strength than ordinary people, and it was entirely possible that he could not push Chen Xiaowang.
