Answer:
(B) the sum total of all matter and energy
Explanation:
Universe comprises of all the matter and energy that exists in space. It contains billions of stars, planets and interstellar matter that is clouds of dust and gas. There is large amount of the empty space in between.
Universe contains stars as many as grains of sand on all beaches on the Earth. These stars are grouped into galaxies. Milky Way is one of the galaxies. Galaxies can be grouped into clusters and super-clusters.
The type of medium affects a sound wave as sound travels with the help of the vibration in particles. As different mediums have different amount and size of particles, for example, the speed of sound is faster through solid than liquid as solids have closely packed particles whereas liquids are loosely packed. Therefore the vibration is quicker in solids than liquids.
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Answer:
friction reduces the efficiency of machines, thus we must reduce the friction force that is acting upon it.
