Stopping Distance for Auto

汽车的停车距离

Assuming proper operation of the brakes, the minimum stopping distance for an automobile is determined by the effective coefficient of friction between the tires and the road. The friction force of the road must do enough work on the car to reduce its kinetic energy to zero (work-energy principle). If the wheels of the car continue to turn while braking, then static friction is operating, while if the wheels are locked and sliding over the road surface, the braking force is a kinetic friction force.

To reduce the kinetic energy to zero:

so the stopping distance is

Show calculation

展示计算

Note that this implies a stopping distance independent of vehicle mass. It also implies a quadrupling of stopping distance with a doubling of vehicle speed.

Even though the stopping distance for a large truck should be the same as that for a car, there are real-world cases where a truck has more difficulty stopping. Runaway truck ramps are placed on long downgrades like this one on Monteagle in Tennessee. Deep, loose gravel provides a stopping force greater than that obtained from just a tire against the road.

尽管大型卡车的停车距离应与汽车相同，但在现实世界中，卡车往往更难停下来。这种情况下，会设置 runaway truck ramps，例如田纳西州蒙特尼格勒的这个坡道。深厚的松散碎石能提供比仅靠轮胎与路面接触所获得的更大的停车阻力。

因此，停车距离是注意到这表明停车距离与车辆质量无关。它还表明，车辆速度加倍时，停车距离会增加四倍。

假定刹车正常工作，汽车的最小停车距离由轮胎与路面之间的有效摩擦系数决定。路面的摩擦力必须对汽车做足够的功，使其动能减少到零（功-能原理）。如果刹车时车轮继续转动，则静摩擦力在起作用；如果车轮锁死并滑动，则制动力是动能摩擦力。为了将动能减少到零：

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Work-energy principle

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Stopping Distance Calculation

停车距离计算

For calculating minimum stopping distance, a value of 0.8 is a nominal value for the coefficient of static friction between good tires and a good road surface. Generally, coefficients of kinetic friction are less, and may be dramatically less for wet, icy, or oily surfaces. For many existing tires, the coefficient of kinetic friction on a dry road surface may approach 0.8 if the braking is not so prolonged as to cause tire melting.

The stopping distance is given by:

Develop expression

推导表达式

You may enter data in any of the boxes above. The quantity will be calculated in the other unit systems. Then click on the active text for either stopping distance or vehicle speed to calculate that quantity. The quantities will not be forced to be consistent until you click on the quantity to be calculated.
Note that this calculation implies a stopping distance independent of vehicle mass. It also implies a quadrupling of stopping distance with a doubling of vehicle speed.

One experiment with trained drivers asked the drivers to stop a vehicle on signal by 1) locking the wheels and 2) stopping as fast as possible without locking the wheels. On dry flat concrete, the stopping distances were very nearly the same. Both test yielded coefficients of friction near 0.8 for tires with new tread on this surface. The coefficient of kinetic friction is anticipated to be considerably less on a wet surface where the water can act as a lubricant. It is also likely that worn tires will have a considerably smaller coefficient of kinetic friction than static friction.

一项对训练有素的驾驶员的实验要求驾驶员在信号发出时通过两种方式停止车辆：1）锁死车轮，2）不锁死车轮尽可能快速地停止。在干燥的平坦混凝土表面上，停车距离几乎相同。两种测试均得到轮胎新胎纹在该表面的动摩擦因数接近0.8。预计在湿滑表面上，水可以起到润滑作用，动摩擦因数会显著降低。此外，磨损的轮胎很可能具有比静摩擦因数显著更小的动摩擦因数。

对于计算最小停车距离，0.8是一个良好的轮胎与良好路面之间的静摩擦因数的名义值。通常，动摩擦因数更小，对于湿滑、冰面或油污表面，可能小得多。对于许多现有轮胎，如果刹车不持续到轮胎熔化，那么在干燥路面上的动摩擦因数可能接近0.8。停车距离由下式给出：如果车辆速度是v = m/s = ft/s = km/hr = mi/hr，则停车距离是d = m = ft。您可以输入数据到上述任何框中。该量将在其他单位系统中被计算。然后点击“停车距离”或“车辆速度”上的活动文本以计算该量。直到您点击要计算的量之前，这些量不会被强制保持一致。请注意，这个计算假设停车距离与车辆质量无关。它还意味着车辆速度加倍时，停车距离会四倍增加。

中文译文中的待填/计算数值依次对应：1：v 2：vc 3：vk 4：vm 5：d 6：dc。实际数值以上方原输入框为准。

Index

Work-energy principle

索引功-能原理

HyperPhysics***** Mechanics

力学

R Nave

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