verlangsamen
to slow down
To reduce the speed of something or someone; to make something slower.
Der Fahrer musste das Auto vor der Kurve verlangsamen.
The driver had to slow the car down before the curve.

to slow down
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to slow down
To reduce the speed of something or someone; to make something slower.
Der Fahrer musste das Auto vor der Kurve verlangsamen.
The driver had to slow the car down before the curve.

The verb 'verlangsamen' (to slow down) is derived from the adjective 'langsam' (slow). The prefix 'ver-' is used here to express a change: to make something slow or to become slow.
Eine gesunde Ernährung kann den Alterungsprozess verlangsamen.
A healthy diet can slow down the aging process.
The prefix 'ver-' is inseparable. It remains firmly attached to the verb stem 'langsamen' in all tenses and sentence constructions.
Er hat sein Tempo nicht verlangsamt.
He did not slow down his pace.
This verb has two main uses: you can actively slow something down (transitive with an accusative object), or something can slow down by itself (reflexive).
Die Polizei verlangsamt den Verkehr.
The police are slowing down traffic.
When you actively slow something down, typical objects are abstract concepts such as: the pace, growth, a process, or development.
Wir müssen das Arbeitstempo etwas verlangsamen, um Fehler zu vermeiden.
We need to slow down the work pace a bit to avoid mistakes.
to brake / slow down
'bremsen' and 'verlangsamen' are very close in meaning because both can mean that something becomes slower. 'bremsen' often sounds more active and stronger: someone or something intervenes, for example with a brake or through an obstacle. It can even go as far as coming to a stop. 'verlangsamen' is more neutral and mainly describes that the speed decreases. With vehicles, people often say 'bremsen' in everyday language. For movements, processes, or changes, 'verlangsamen' often fits well, especially when it happens slowly and step by step.

Wegen der schlechten Verbindung verlangsamt sich der Download.
Because of the poor connection, the download is slowing down.
Lea bremst vor der Kurve, weil die Straße nass ist.
Lea brakes before the curve because the road is wet.