The discussion centers around the stopping distances of vehicles under different braking conditions, specifically comparing locked wheel skidding to rolling, braked wheels in conventional, non-ABS vehicles. Participants explore the mechanics of friction involved in these scenarios, including the coefficients of static and kinetic friction, and the implications for vehicle control and stopping efficiency.
Participants express differing views on the relationship between skidding and stopping distances, with no consensus reached. Some argue that skidding leads to longer stopping distances due to kinetic friction, while others challenge this notion, suggesting that under certain conditions, skidding may not always result in longer distances. The discussion remains unresolved regarding the exact dynamics and implications of friction in these scenarios.
Participants note that the coefficients of friction may vary based on conditions such as tire damage, road surface, and the dynamics of braking. There are references to the effects of overheating brakes and the design of clutches in vehicles, indicating that these factors could influence the discussion but are not fully explored.
mgb_phys said:Whats the friction in both cases?
The point is that it's not!Langmarais said:The co-efficient of friction of the road surface is constant/ same in both.
For dry roads, the stopping distance is less for the skidding vehicle.Langmarais said:Why is it that a vehicle travels further when skidding with locked wheels than when decelerating with rolling, braked wheels in conventional, non-abs vehicles.
No, just the opposite. Otherwise anti-lock brakes would serve no purpose--just jam on the brakes and skid.sganesh88 said:For dry roads, the stopping distance is less for the skidding vehicle.
No. Once the tires skid, you are dealing with kinetic friction and not static friction. And kinetic friction, being less than static, leaves you with less control of your vehicle. That's why you don't want your tires to skid.sganesh88 said:@Doc Al
Why is that? If we assume that the tire isn't notably damaged by skidding, the coefficient should be almost the same right?
The main purpose of ABS is to maintain directional control - which is possible only when the wheels are rotating- and not reducing the stopping distance.. But ya. I did the calculations and saw the rolling vehicle will stop sooner. The skidding vehicle screeching through the road makes me think its losing energy faster. Thats not the case though. :(Doc Al said:No, just the opposite. Otherwise anti-lock brakes would serve no purpose--just jam on the brakes and skid.
mgb_phys said:The point of the question though, is that in one case you have rubber+road * weight of car and in the other you have steel disc+brake shoes * force of hydraulics
Yes. But the only external force is friction. So one can prove that the rolling car will stop faster than the skidding assuming that the friction at pads is high enough to support equivalent deceleration of the wheel..mgb_phys said:The point of the question though, is that in one case you have rubber+road * weight of car and in the other you have steel disc+brake shoes * force of hydraulics
Except in the case of overheated brakes (or really bad design), the dynamic coefficient of friction at the brake pads is always enough to maximize braking.sganesh88 said:Yes. But the only external force is friction. So one can prove that the rolling car will stop faster than the skidding assuming that the friction at pads is high enough to support equivalent deceleration of the wheel.
Lsos said:Place a heavy book on a table and gently try to push it. You'll notice it is harder to get it moving than it is to keep it moving. It's because static friction is higher than sliding friction. Same mechanism works in tires...
Doc Al said:No, just the opposite. Otherwise anti-lock brakes would serve no purpose--just jam on the brakes and skid.
No. Once the tires skid, you are dealing with kinetic friction and not static friction. And kinetic friction, being less than static, leaves you with less control of your vehicle. That's why you don't want your tires to skid.
The first thing to understand is the difference between static friction and kinetic friction, and that in most situations the coefficient of static friction is greater that the coefficient of kinetic friction. (Consider the sliding book example brought up by Lsos.)Langmarais said:Could you please elaborate and explain the application of static/ kenetic energy theory in the case study as per the original example. I am not a physics expert and would like to understand.