rotational speed
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rotational speed
A physical quantity that indicates how often an object rotates around its own axis within a specific unit of time. It is often measured in revolutions per minute (rpm).
Der Motor erreicht bei hoher Geschwindigkeit eine Drehzahl von 6000 Umdrehungen pro Minute.
At high speed, the engine reaches a rotational speed of 6000 revolutions per minute.
The word is a compound made from the stem of the verb 'drehen' (to turn/rotate) and the noun 'die Zahl' (number). So it literally means the 'number of rotations'.
Die Drehzahl gibt an, wie schnell sich der Motor dreht.
The rotational speed indicates how fast the engine is turning.
'Drehzahl' (rotational speed) is often used with the verbs 'erhöhen' (to increase), 'senken' (to lower), or 'regeln' (to regulate). Typical adjectives are 'hoch' (high), 'niedrig' (low), or 'konstant' (constant).
Beim Anfahren muss man die Drehzahl langsam erhöhen.
When starting, you have to increase the rotational speed slowly.
In a technical context, rotational speed is usually given in the unit 'Umdrehungen pro Minute' (revolutions per minute), often abbreviated as 'U/min' (rpm).
Die maximale Drehzahl dieses Geräts liegt bei 3000 Umdrehungen pro Minute.
The maximum rotational speed of this device is 3000 revolutions per minute.
speed
'die Geschwindigkeit' and 'die Drehzahl' can both have to do with movement, especially in vehicles or machines. 'Geschwindigkeit' says how fast something moves from one place to another, for example a car on the road. 'Drehzahl' says how often something rotates around its own axis, for example an engine or a wheel. Learners may confuse the words because in a car both can be important at the same time. In practical terms: on the speedometer you see the speed, while with the engine people often talk about the rotational speed.
Wenn die Drehzahl des Motors zu hoch ist, sollte man in einen höheren Gang schalten.
If the engine's rotational speed is too high, you should shift into a higher gear.
In der Stadt darf die Geschwindigkeit oft nicht höher als 50 Kilometer pro Stunde sein.
In the city, the speed often must not be higher than 50 kilometers per hour.