Can sound travel through a vacuum (empty space)?

Yes — sound travels through space at the speed of light Yes — sound doesn't need matter, only energy No — sound is a mechanical wave that requires a medium (particles) to carry its compressions and rarefactions Only very loud sounds can travel through a vacuum

Sound travels at about 340 m/s in air, 1,500 m/s in water, and about 5,000 m/s in steel. What does this pattern tell us?

Sound travels faster in air because air is lighter, so the wave moves easily Sound travels faster in denser, stiffer media because particles are closer together and transmit vibrations more efficiently Sound speed is the same in all media — the differences are due to measurement error Sound travels slower in water because water resists compression more than air

You see a lightning flash and hear the thunder 3 seconds later. Roughly how far away was the lightning? (Sound travels ~340 m/s in air.)

About 113 metres About 1,020 metres (roughly 1 km) About 3 km About 10,200 metres (10 km)

What physical property of a sound wave corresponds to its pitch?

Amplitude — larger waves have higher pitch Wavelength — longer wavelength waves have higher pitch Frequency — higher frequency produces a higher pitch Speed — faster waves sound higher pitched

What is the Doppler effect?

The slowing down of sound as it travels through denser materials The apparent change in frequency of a wave when the source and observer are moving relative to each other The fading of a sound wave as it travels further from its source The change in sound speed when temperature increases

What is the range of frequencies that humans can typically hear?

0 Hz to 1,000 Hz Approximately 20 Hz to 20,000 Hz (20 kHz) 100 Hz to 100,000 Hz 1 Hz to 1,000,000 Hz

Ultrasound (above 20,000 Hz) is used in medical scanning. Why use ultrasound rather than lower-frequency sound?

Ultrasound travels faster, reaching deep tissue before the energy is absorbed Lower frequency sounds cause pain to patients; ultrasound is painless Higher frequency means shorter wavelength, allowing imaging of finer details — and ultrasound is safe for tissue unlike X-rays Ultrasound reflects better off liquids, which is why it works for scanning blood

Why does sound get quieter the further you are from the source?

Sound particles slow down and stop as they travel The wave energy spreads over an increasingly larger area (proportional to distance squared), so less energy reaches your ears Air resistance removes energy from the sound wave proportional to distance The frequency decreases as the sound travels further from the source

A bat uses echolocation to catch insects. It emits a pulse of ultrasound and detects the echo returning from a moth 0.02 seconds later. How far away is the moth? (Speed of sound in air ≈ 340 m/s.)

6.8 metres 0.17 metres 3.4 metres 17 metres

Why does sound travel faster on a warm day than a cold day?

Warmer air is less dense, so the sound wave has less resistance to travel through Warmer air molecules move faster on average, so compressions are passed between molecules more quickly Heat adds energy directly to the sound wave, speeding it up Sound speed is constant in air and does not change with temperature