-- The area under a velocity/time graph, between two points in time, is the difference in displacement during that period of time.
-- The area under a speed/time graph, between two points in time, is the distance covered during that period of time.
Closed system. If the system is not closed, matter or energy can escape from the system. an example of this is if you react magnesium and hydrochloric acid in a open system. The H₂ gas is going to escape making it look like some of the mass disappeared . in that same reaction some in an open system will also loose heat to the surrounding which will make it look like less heat was produced.
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That tells you that one of two things has happened:
Either
-- the source began emitting sounds with lower frequency
or
-- the source began moving away from you, and the
apparent change is due to the Doppler effect.
Some scienist think it was just a rock metal or ice hope i helped :L