Kinetic friction and regenerative braking dilemma

In summary: Clearly the car velocity matters since KE = 1/2 m v^2, so the same rate of deceleration at a higher speed means more energy consumed per unit of time, but I was wondering if the speed of the tire surface matters in a skidding situation, and apparently it does.
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rcgldr
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Assume a car has a smart regenerative braking system that optionally locks up the wheels with the tires skidding or allows the wheels to rotate while skidding, using the torque from the rotating and skidding tires to generate power into some type of kinetic energy recovery system. Assume the coefficient of kinetic friction is the same in both cases.

In the first case with the wheels locked up, all of the reduction of kinetic energy of the car during braking is converted into heat. In the second case with the wheels rotating, some of the reduction in kinetic energy is transferred into the kinetic energy recovery system, and the rest of it converted into heat by the skidding tires.

The dilemma here is that it seems the heat produced by kinetic friction would be the same regardless if the wheels are locked up or rotating but still skidding, but in the second case some of the kinetic energy is going into the kinetic energy recovery system.

I'm wondering if the relative velocity between tire surface and road while skidding makes a difference, base on the formula that power equals force times velocity.
 
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  • #2
rcgldr said:
The dilemma here is that it seems the heat produced by kinetic friction would be the same regardless if the wheels are locked up or rotating but still skidding,
Why would you assume that? If they are locked up completely then the "slipping rate" will be higher than if they are rotating but still skidding. Surely there should be higher frictional losses with a faster slipping rate, all other things equal.
 
  • #3
rcgldr said:
The dilemma here is that it seems the heat produced by kinetic friction would be the same regardless if the wheels are locked up or rotating but still skidding, but in the second case some of the kinetic energy is going into the kinetic energy recovery system.

DaleSpam said:
Why would you assume that? If they are locked up completely then the "slipping rate" will be higher than if they are rotating but still skidding. Surely there should be higher frictional losses with a faster slipping rate, all other things equal.

Which is why I continued with (this was an edit (text went blank while I was trying to compose message), maybe we cross posted)).

rcgldr said:
I'm wondering if the relative velocity between tire surface and road while skidding makes a difference, base on the formula that power equals force times velocity.

Clearly the car velocity matters since KE = 1/2 m v^2, so the same rate of deceleration at a higher speed means more energy consumed per unit of time, but I was wondering if the speed of the tire surface matters in a skidding situation, and apparently it does.
 
Last edited:

1. What is kinetic friction and how does it affect regenerative braking?

Kinetic friction is the force that acts between two surfaces in contact when they are moving relative to each other. In the case of regenerative braking, this force works against the motion of the wheels, converting some of the kinetic energy into heat and reducing the effectiveness of the regenerative braking system.

2. How does regenerative braking work?

Regenerative braking is a system that allows a vehicle to recover some of the kinetic energy that is lost during braking. It works by using an electric motor to slow down the vehicle and convert the kinetic energy into electrical energy, which can then be stored in a battery for later use.

3. What is the dilemma with regenerative braking?

The dilemma with regenerative braking is that while it can save energy and increase the efficiency of a vehicle, it is not always the best option for stopping the vehicle. This is because the conversion of kinetic energy to electrical energy is not 100% efficient, and in some situations, traditional friction braking may be more effective.

4. Are there any downsides to using regenerative braking?

Yes, there are some downsides to using regenerative braking. One of the main concerns is that the regenerative braking system adds weight and complexity to the vehicle, which can increase the cost of production and maintenance. Additionally, the system may not work as effectively in extreme weather conditions.

5. Can regenerative braking be used in all types of vehicles?

While regenerative braking is most commonly used in hybrid and electric vehicles, it can also be implemented in traditional gasoline and diesel vehicles. However, the effectiveness of regenerative braking may vary depending on the type of vehicle and its driving conditions.

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