3 ms·
Brakes _do_ stop a car. You're converting energy of motion into heat. That is not the tires doing that. You are not transferring significant amounts of energy i
by mlindner 4y ago
Brakes _do_ stop a car. You're converting energy of motion into heat. That is not the tires doing that. You are not transferring significant amounts of energy into the road or into heating up the tires.
Now in the case of regenerative braking, the losses from the charging do also dissipate the energy, but most of it goes back into the battery to be used for driving which, over time, is transferred into the tires and the air.
It's important to remember that ideal wheels are not actually moving with respect to the surface they roll over. From the tire's perspective the road is not moving in any direction other than up and down, repeatedly touching the tire and then not touching it again at different points. As long as you maintain static friction when braking and don't start skidding, for ideal wheels, you're not transferring any energy to the tire or to the road.
Now, real tires are not ideal wheels so there's some differences, but those are minor components compared to the majority of energy being dissipated in charging the battery or into heating up/wearing down brakes. And indeed when driving, the majority of loss of energy is from air resistance, not the tires.
- rootusrootus 4y ago> Brakes _do_ stop a car. Sure, from a lay perspective. Though I stop my car routinely without ever touching the brakes. Even my gas car does a non-trivial amount of braking without using friction pads. But the point stands. Brakes don't touch the road, the tire does, so it matters not at all how you apply force to the wheel, from the perspective of the tire-to-road interface it's all the same. If we want to have some fun with the physics, brake pads don't use dynamic friction to stop the car, either. Not most of the time, at least. Which is why they last as long as they do.
- mlindner 4y agoI was responding to the idea in the previous post that it was somehow that tires stop the cars rather than brakes or regenerative braking. > Brakes don't touch the road, the tire does, so it matters not at all how you apply force to the wheel, from the perspective of the tire-to-road interface it's all the same. This is not the case. Brakes (or regenerative braking) absorb the energy of motion into heat or stored chemical energy. The tires are not doing the stopping. > brake pads don't use dynamic friction to stop the car This is also incorrect. Brake pads are using almost completely dynamic friction to stop the car. From the perspective of the brake bads the tire is moving and from the perspective of the tire the brake pads are moving. There's no static friction involved there.