How does a car differential work?

The car differential is a mechanism that enables the left and right (or front and rear) drive wheels to rotate at different speeds. It is mainly composed of left and right half-axle gears, two planetary gears and a gear rack. The function is to make the left and right wheels roll at different speeds when the car is turning or driving on uneven roads, that is, to ensure that the drive wheels on both sides perform pure rolling motion. The differential is installed to adjust the speed difference between the left and right wheels. In four-wheel drive, in order to drive the four wheels, all wheels must be connected. If the four wheels are mechanically connected together, the car cannot rotate at the same speed when driving in a curve. In order to make the car's rotation speed basically consistent when driving in a curve, an intermediate differential needs to be added to adjust the speed difference between the front and rear wheels.
 
This adjustment of the differential is automatic, which involves the "minimum energy consumption principle", that is, all objects on the earth tend to consume the least energy. For example, if a bean is put into a bowl, the bean will automatically stay at the bottom of the bowl and will never stay on the wall of the bowl, because the bottom of the bowl is the lowest energy position (potential energy), it automatically chooses to be still (minimum kinetic energy) and will not move continuously. In the same way, when turning, the wheels will automatically tend to the state with the lowest energy consumption, and automatically adjust the speed of the left and right wheels according to the turning radius.
 
When turning, due to the phenomenon of drag on the outer wheel and slip on the inner wheel, the two driving wheels will generate two additional forces in opposite directions. Due to the "minimum energy consumption principle", the rotation speeds of the wheels on both sides will inevitably be different, thus destroying the balance relationship between the three, and reflected on the half-axle gears through the half-axle, forcing the planetary gears to rotate, slowing down the speed of the inner half-axle and speeding up the speed of the outer half-axle, thereby achieving the difference in the speed of the wheels on both sides.
 
If the driving wheels on both sides of the drive axle are rigidly connected with a whole shaft, the two wheels can only rotate at the same angle. In this way, when the car turns, the outer wheel will slide while rolling, while the inner wheel will slip while rolling, because the outer wheel has to move a greater distance than the inner wheel. Even if the car is driving in a straight line, the wheels will slide due to uneven road surface or different rolling radius of the tires even though the road surface is straight (tire manufacturing error, different wear, uneven load or unequal air pressure).