system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why don’t automatic cars stall at traffic lights?

I understand they use a clutch, but how come the power is instant and there is no lag/it’s smooth to accelerate?
gpt
They don't use a clutch. Instead they use a fluid coupling called a torque converter which works kind of like one turbine spinning another with transmission fluid, or think of one fan blowing another fan to make it spin. The torque converter is designed to allow the input and output shafts to spin at different speeds, including one being stopped completely. When power is applied the u get smooth acceleration because the fluid absorbs a lot of it.