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rssh

ABS-a physics concept got wrong.

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ABS stand for anti lock braking system which applied brakes 15 times a second when it senses the wheel about to lock up.

 

Recently this new technology is getting famous in all the car segment like the V-TEC is getting ABS option and even the hatches are not far behind.

 

PHYSICS CONCEPT-

According to friction law the coefficient of friction of rolling is much less compared to sliding friction that why wheels are used in cars.

My question is that the car equipped with ABS has lesser stopping distance than normal one (check new V-tec) ,when the wheels lock up in a car without ABS the wheels slide so the rolling motion coverts to sliding motion so the car should take lesser stopping distance but In a car with ABS the wheels don't slide and rolling motion is maintained so how come it takes less distance (I am just talking abt braking distance and not ability to steer the car  with ABS). Remember that the vehicle brake in the same surface.

WHY?????smiley3.gif

 

 

[Guys its a request that you don't write abt ABS as I know what it is ]

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Car and Driver in the 90s did a test between ABS and non ABS car, the non ABS car was driven by experts, consistently, the non ABS car out-braked the ABS equipped car by 15-20%, both cars were same model. It was found in the end that modulation with 33% lock up works out to be the best formula for braking. One of the reasons I removed my ABS module in my Accord, maybe tech has changed now and there is more processing power available to today's ABS but in the 90s, experience and the right amount of foot pressure got you stopped faster than ABS provided you were aware of what you were doing.

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Basic point of having an ABS system is to be able to provide the driver with steering control during emergency braking.

 

In a non ABS car, on emergency braking the wheels would lock up and car would continue in the directionn it was last pointing before the lock up. This is dangerous as the driver cannot steer away from an obstacle.

 

In a ABS car, the system prevents the wheels from locking up which helps the driver to retain steering and hence avoid crashing into something.

 

The primary purpose of ABS is to retain steering control in emergency situations and not necessarily for reducing braking distance.

 

FRG

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Basic point of having an ABS system is to be able to provide the driver with steering control during emergency braking.

 

In a non ABS car' date=' on emergency braking the wheels would lock up and car would continue in the directionn it was last pointing before the lock up. This is dangerous as the driver cannot steer away from an obstacle.

 

In a ABS car, the system prevents the wheels from locking up which helps the driver to retain steering and hence avoid crashing into something.

 

The primary purpose of ABS is to retain steering control in emergency situations and not necessarily for reducing braking distance.

 

FRG
[/quote'] Well FRG i knoe this but how come an ABS fitted car has lower stopping distance than no ABS one ,forget the steering for a moment.

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Basic point of having an ABS system is to be able to provide the driver with steering control during emergency braking.

 

In a non ABS car' date=' on emergency braking the wheels would lock up and car would continue in the directionn it was last pointing before the lock up. This is dangerous as the driver cannot steer away from an obstacle.

 

In a ABS car, the system prevents the wheels from locking up which helps the driver to retain steering and hence avoid crashing into something.

 

The primary purpose of ABS is to retain steering control in emergency situations and not necessarily for reducing braking distance.

 

FRG
[/quote'] Hey you didn't get my question how come an ABS fitted car take lesser stopping distance than non-ABS one forget the steering for a moment.rssh2007-10-29 20:21:28

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Thats because most drivers cannot modulate the pressure on the brakes like the ABS. Maximum friction is generated right up till the moment of lock up. Once the car begins to slide, there is very less friction to really stop the car.

 

FRG

 

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so why did the earlier cars with ABS took more distance than non-ABS one . So you mean to say that rolling friction is more than sliding friction for a body with same mass . Its magic.

 

 

If someone can explain it with equation then it will be helpful. I LOVE PHYSICS.
rssh2007-10-29 20:32:05

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Thank FRG I am flattered !!!! the tires have static friction and not kinetic ,I thought vice versa .Thanks for clearing my doubt. (thats why in drifting the tires burn faster.) 

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The link explains the friction ver well.

 In panic braking the average driver just jams on the brakes. So

1. He gets into the kinetic braking band and this increases the stopping distance.

2. With the wheels locked he loses steering control. FWD with its lopsided weight distribution makes this worse. Weight transfer in hard braking makes the front even 'heavier', so rear wheels tend to lock quickly. That is why you see the rear trying to 'overtake' the front of the car!

On the other hand ABS prevents the brakes from locking. Modern ABS systems monitor the wheel rotation, and when they detect that the rotation significantly lower in a particular wheel (locking is imminent) while others are still be rotating it momentarily releases the brake until the errant wheel starts revolving. This 'pumping' action is controlled by sensors and the frequency varies with the requirements. In other words the sensors 'modulate' the ABS action.

In the older generation ABS systems this modulation was missing. Once the ABS was triggered the pumping frequency was invariant (and far lower), irrespective of the conditions. This is why an expert could out-brake the ABS. However, the average John Doe still benefited since event these systems gave far shorter braking distances than locked wheels, and with steering control.

Added: Also, in modern cars ABS may work separately on each wheel, while the first generation systems worked on the entire braking system. So they released brakes even on the wheels not yet locked!

Today things are different. A good ABS will outdo almost all experts. Traction Control in F1 cars is fast enough to modulate the engine power when wheels start slipping !

FRG: Your mail box is full. I was away for five days.

sgiitk2007-10-30 12:07:50

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