Brainings

Energy

Photo Jun 07, 10 37 02 AM

Most of my job consists of keeping track of energy. If I know how much energy I have coming in I can figure out how much energy I need to have going out. Then I can properly size a pump or heater or chiller, and tell the electrical engineers how much energy they need to give me to make my energy balance work. Energy is an interesting thing. It’s neither created or destroyed. It just is. It gets converted into many forms (motion, light, heat, electricity). So, when I see comparisons like the one above, from Brembo’s Facebook page, it strikes a chord with me. You see, according to Brembo, in one lap of the Circuit Gilles-Villeneuve for the GP Montreal a Formula 1 car will convert enough energy into heat and electricity (for KERS) from its brakes to power an electric scooter around the 4.361 km course four times. After all, it’s just energy.

[Image Credit: Brembo]

  • I remember the first time someone told me that brakes were a machine that converted motion into heat.

    [youtube OT4B-NJUcZE http://www.youtube.com/watch?v=OT4B-NJUcZE youtube]

    • And electric scooters can turn normal people into utter dweebs. Just think of what would happen if I got on one! Dweeb singularity, that's what I'm talking about. Neo-Maxi-Zoom-Dweebie. Things nearby would start dweebifying by osmosis.

    • Abe

      I know this will be unpopular but I feel that the notion that brakes convert motion into heat is utter BS. Heat is a byproduct of the action but not the result.

      • B72

        The energy doesn't just go away. If you want less motion, you need to convert the kinetic energy into some other kind of energy.

        On hybrids and electrics, regenerative brakes convert motion into electrical energy.
        There are flywheel systems on some race cars (F1?) that convert motion of the car into motion of the flywheel.
        When you slow down by downshifting, you are using the engine to convert the motion of the car into heat and noise.
        When you slow down by coasting, you are very slowly converting motion into a little bit of heat via air drag and mechanical friction
        When you slow down by coasting up a hill, you are converting motion into potential energy (the ability to go back downhill).
        And yes, traditional car brakes convert the motion of the car into thermal energy (heat).

        This is how engineers see the world. Why? Because the concept of conservation of energy allows us to correctly predict how things will work. It's a pretty basic and important concept in the engineering world.

  • monkey_tennis

    The thing I want to ask an engineer about brakes is "what is the thermodynamic mechanism that explains brake fade?"

    I get that the brakes are basically converting kinetic energy to heat — but what changes at a key temperature point that means that this mechanism suddenly becomes MUCH less effective? Is it even an effect at the brake disks/pads/drums; or is it just the point where heat sink back into the hydraulics makes that system ineffictive.

    Surely some Hoon-gineer can explain this in simple enough terms that I can follow?…

    • skitter

      Brake fade can happen either at the pad/disk/drum, or in the hydraulic system.
      1. At the pad/disk/drum, the materials get so hot that the friction is reduced.
      AND/OR
      2. By the brake pistons, the brake fluid can boil so the pedal no longer applies force through the vapor.
      Before either of those can happen, the whole system has gotten hot, and its surroundings have gotten hot. A brake in cool air gets rid of heat, so it can take more motion and generate more heat, and get rid of that heat. A brake in hot air can't get rid of heat as well. If it gets to the point of fading, it can't get rid of the motion as well, and keeps getting worse until the driver can stop using the brakes and let them cool.

      • monkey_tennis

        Thank you skitter — that all makes sense now.

        I guess the bit I didn't realise was that the friction of the pad/disk/drum typically reduces as it gets too hot: That explains why it is no longer so effective at converting knetic energy to heat. Hence the 'fade'.

        (It also explains why I am not an engineer!)

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