Generate a topic word for the given sentence. A topic word is usually the name of a person, place, animal, concept or object the sentence is focusing on.

platinum is a soft, heavy, white metal.
platinum

escape velocity is the initial speed that something would need to completely escape the gravity of a large body, like a star or a planet (such as the earth), by mere inertia.
escape velocity

johann heinrich schmelzer (born austria some time between 1620 and 1623; died in prague some time between 29 february and 20 march) was a german composer.

johann heinrich schmelzer