RPM refers to the speed of rotation in a minute. It is used as a measure of how fast any machine works at a given time. In cars, the rpm shows how many crankshaft the engine rotates every minute and how many times each piston goes up and down in its cylinder.
Many cars have a tachometer to indicate engine RPM. It is usually measured in thousands. At the top of the tachometer range there is a zone called the red line. Usually highlighted literally. Beyond the red line, the engine can cause damage to the engine.This is really a concern for manual transmission vehicles. For vehicles with automatic transmission, the engine is programmed to switch before it reaches the red line.
The RPM rises as the car accelerates. Therefore, when the vehicle accelerates, RPM rises. However, when the gear is changed according to speed, it also decreases. Increasing the RPM can cause damage to the engine of the car