The friction between the car and the ground when driving is rolling friction, which belongs to the field of static friction. This friction is the same as the friction between the track and the ground when a tracked tank moves forward, and it is static friction.
While sliding friction is constant, relative movement occurs between some point in the contact process and the contact surface - i.e. the wheel “slips,” resulting in sliding friction.
Thus, in normal driving, there is rolling friction; when braking hard, it slips, which is sliding friction.
In life: When an object on a horizontal treadmill moves at a constant speed, there is no friction; When an object moving diagonally upward is stationary on the treadmill, static friction occurs.
When a person walks, thefriction act on it?
I think it should be faster where friction is low.
Because of this, the resistance is reduced and the car wheels will spin very quickly.
p>This mechanic is involved. There is a well-known law in physics that internal forces cannot do work, only external forces can do work. So, for a car, the rotation of the wheels is the internal force. It stands to reason that if there is only rotation with no external force, the car will not move. Here, friction acts as an external force. Many people think that friction can become resistance, so the greater the resistance, the slower the car will be. However, the greater the friction, the greater the external force, but you need to pay a little more fuel. There is no fuel limit here.
The resistance f=umg, V=P/f, traction is provided by the motor andForward power is provided by friction between the wheel and the ground. The resistance must have a certain range before it can be. said that the bigger the better.
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Um, I suddenly thought of this question, but Baidu got a lot of facts instead of answers. My point is work.
Does friction work when a person walks? From this sentence, we can see that “person” here refers to a whole or system, not feet. Therefore, human movement at present cannot be equated with the movement of the feet, but must be equated with the movement of the center of gravity. When a person walks, his feet alternately support each other. When the foot tends to slide forward relative to the ground, the frictional force moves backward, and vice versa. Since people as a system move forward relative to the ground, we can roughly think of the force ofhe friction and the horizontal component of the person's backpedaling force are equal in magnitude and opposite in direction. In other words, the friction force moves forward and, although the feet do not move relative to the ground, the person's center of gravity moves forward relative to the ground. Friction therefore has a positive effect.
In order to deepen understanding, you can give such an example. A long pole with a uniform distribution of masses is erected on an absolutely smooth horizontal surface. When the pole falls, how does the pole's center of gravity shift? The answer is that the center of gravity falls vertically from half the height to the horizontal plane. Because there is no force acting on the long rod in the horizontal direction. But what if it's not a smooth horizontal surface? If the long pole falls forward, the bottom must be subjected to forward friction. At that moment, theforward distance from the center of gravity of the long pole corresponds to the displacement of the long pole, so that the friction force does positive work.
This example is very similar to that of people walking. There is no relative movement of the contact surface, but the center of gravity of the system does. To determine whether an object has a displacement, the most important thing is to determine its center of gravity rather than its contact surface.
Second, let me refute the point of view in the answer above. The answer above mentioned that "cars obtain energy by relying on ground friction, and cars can also use no fuel." is false. Car tires are a rolling process. The contact area between the tire and the ground will move backward relative to the ground, and the ground will move forward against the friction force of the car, so the friction force will do work positif. This friction force and the force of the tire rotating backwards form a pair of action force and reaction force. If the tire did not rotate, there would be no friction. Naturally, the car will not move forward. Therefore, the energy required for the forward motion of the car comes from the rotation of the car's tires. It is not true that it can move without fuel.