The gears in the transmission aren’t actually turning, so why does a little gas keep me from rolling back but also not going forward?
In: 3
There’s a special mechanism called a “clutch” that, oversimplified, controls how “tightly” the engine’s rotation is tied to the transmission’s rotation. If the clutch is fully engaged, the engine’s rotation and the transmission’s rotation MUST match, and if the transmission isn’t moving the engine halts. If the clutch isn’t engaged, the engine spins freely with no connection to the transmission. At levels in between, the motor might be spinning more than the transmission.
In a manual transmission, you generally can’t do what you’re saying easily. If you aren’t careful with the clutch, fully engage it, and don’t gain forward movement, the engine stalls. So starting the car moving uphill involves a lot of coordination where you push the gas and *slowly* engage the clutch so the wheels can start turning with only *partial* connection to the engine before you let the clutch fully engage. That way the engine doesn’t stall.
In an automatic transmission, the transmission handles all of that for you so the engine doesn’t stall.
Some drills have clutch mechanisms like that so they don’t strip screws if you’re using them as a screwdriver. When the screw resists the rotational force more than a certain amount, the clutch disengages and disconnects the drill motor from the bit. They make a lot of noise as the clutch engages, meets resistance, disengages, and repeats over and over again.
Same kind of principle in an automatic transmission, it’s letting the engine push *just hard enough* to keep the wheels from spinning backwards but staying *just disengaged enough* the motor can keep spinning.
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