In science fiction films, huge explosions in space are often shown with a loud roar. In real space, far from any planet, why would that explosion actually make no sound at all to a nearby astronaut?
- Light travels faster than sound, so the explosion would be seen long before any sound reached the astronaut, though the sound would eventually arrive
- Sound waves are absorbed by the astronaut's spacesuit before they can be heard, unlike light waves which pass straight through
- The human ear cannot detect sound at the extremely high frequencies produced by explosions, even though the sound does travel through space
- Sound waves need particles of matter, like the molecules in air or water, to vibrate and carry the wave, and space is a near-total vacuum with essentially no particles to vibrate
Why D? And why not the others?
Correct answer: D. Sound waves need particles of matter, like the molecules in air or water, to vibrate and carry the wave, and space is a near-total vacuum with essentially no particles to vibrate
Sound is a mechanical wave, meaning it travels by making particles of a medium, like the molecules in air, water or a solid, bump into their neighbours and pass the vibration along. In outer space there is only a near-total vacuum with essentially no particles to carry that vibration, so an explosion there would be silent to any nearby observer no matter how powerful it was. The option about light outrunning sound is wrong because it assumes the sound eventually arrives, when in reality there is no medium present for it to travel through at all. The option about a spacesuit absorbing sound is wrong because it ignores that the sound could not reach the suit in the first place, since it cannot propagate through the vacuum surrounding it. The option about frequency is wrong because it wrongly assumes the sound is produced and simply inaudible, rather than never transmitted beyond the explosion itself.
Source: BBC Bitesize GCSE Physics: Sound waves