Quote:
Originally Posted by stefanv
Yes, you're transferring the same number of Newtons (force), but you're expending more power while producing those Newtons (thus, less efficiently). That extra power has to go somewhere. Since it isn't going into making the car move, it is going into removing material from the clutch and making it hotter.
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The extra power has to go somewhere, but it doesn't have to go into the clutch disc. Just like revving in neutral, the energy goes into spinning the flywheel.
If revving with the clutch dragging created more friction, the car would move. You cannot create more heat in the clutch disc without more friction, and more friction would cause the the car to move, especially as friction comes first, heat is generated from friction.
My Ford has a hand crank handle. How much power can I exert with my arms? Tiny amount of power.
An electric starter takes 80A - cranking a hot engine takes 1 second. That's ~80mah.
Moreover, if a bump start caused the same wear as a 2000rpm start, you would experience the same change in motion. I don't feel a thing as my clutch spinning at ~2000rpm just kisses my flywheel accelerating my engine to the ~90rpm required for it to fire up. Once it fires, I rev match and I'm off.
I'm a semi-pro wood worker, and I think there are a lot of flaws with the sander analogy. When I first built my workshop, I did a feature beam running the whole width of the shop. I started hand sanding the whole thing - then switched to the belt sander - it was barely any faster, just less tiring since the motor was doing the work. The ~2kg weight of the sander means it's exerting more force than I could on a similar sized sanding float and still be able to push it across the surface. The speed of the belt ejects saw dust- hand sanding means regular stopping as your sand paper rides on it's own layer or saw dust reducing it's cutting power. Finally of course, a power tool doesn't stop/start at the end of it's stroke- which costs time.
Yes, I can take off more wood than a sander with just one heavy stroke, I can use a jack plane. I can also use a file/ rasp to take of a lot of material in a single stroke, using lots of pressure, or I can use less pressure and and go back and forth and do less work.
An example of a hand tool moving slower, having to stop and change direction and yet doing the same amount of work:
Power tools are just for lazy people.