system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If I'm in an automatic transmission car on a slight hill and I press the gas just enough to stop myself from rolling back, so I'm not moving, how does the engine not stall?
gpt
An automatic transmission has a device in it called a torque converter. It is essentially a big hollow donut shaped cylinder with two blades in it, and the cylinder is filled with transmission fluid. When the engine is running but the wheels aren't moving, the blade is just spinning inside the torque converter and most of the engine torque is being transmitted into the fluid. So the engine is still doing work, but it's doing work on the fluid instead of on the wheels.