Eli5. What makes the sound in car engine sounds.
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There are rotating metal pieces, tiny explosions, the exhaust from those explosions, and the tires against the road. The little “tink and click” noises when you turn off the car is the metal cooling and contracting after being warmed up and expanded during use.
Ever piston cycle is a confined explosion. That makes a little noise, even if it’s silenced quite effectively. Before every explosion there is a sudden rush or pulse of intake air, this is also a large component of the sound. The rest is gears, belts and impellers whirring.
The hot exhaust from the combustion cylinders decompressing as it passes from the engine through the baffled expansion chambers of the muffler before exiting out the tailpipe. Without those baffled chambers the sound would be extremely loud.
Internal combustion engines have thousands of little explosions (combustion) inside them (internal).
These little explosions create sound. They also move parts inside the engine which makes even more sound. Also, when the exhaust (smoke) from the explosions comes out, that makes sound too.
The overwhelming majority of the noise is due to combustion, and particularly the expansion of hot gases out through the exhaust valves into the tailpipe. While these are individual, discrete events, once those events occur often enough (somewhere around 20-30 events per second, or 20-30 Hz), your brain stops interpreting the noises as discrete sounds and instead interprets them at a continuous tone at a specific frequency correlating with the engine speed.
Increasingly in modern cars, it’s speakers playing what sound engineers think you want to hear when you hit the gas pedal.
It is a symphony of sounds. One can use a mechanic’s stethoscope to isolate the various hums, whirrs, clatters, and rumbles. Helpful when diagnosing some problems–potential problems.
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