Sound Needs a Messenger
The bell in the jar — no air, no sound
What this lesson covers
Why it matters
In space movies the explosions ROAR. In real space they wouldn't even whisper. One bell, one jar and one pump have been proving it for 350 years.
Predict first
A ringing bell is sealed in a jar and the air is slowly pumped out. You will…
Sound is carried by a messenger — air, water or solid. Remove the messenger and the message stops. Light needs no messenger, so you still see the hammer striking.
- still SEE it ringing, but the sound fades to nothing — correct
- hear it just the same
- stop seeing AND hearing it
What you do
Pump the air out and watch the volume die while the bell keeps swinging — then let the air rush back in.
Check yourself
Sound travels FASTEST through…
Packed particles pass the vibration quickest: solids beat liquids beat gases — and vacuum carries nothing at all.
Why do astronauts on a spacewalk need radios to chat?
Radio waves cross the vacuum happily; sound cannot — no messenger, no message.
A soundproof box works best when lined with…
Soft foam and cloth soak up the vibrations instead of bouncing them — the Selina soundproof-box activity in one line.
- solids like steel — the particles are packed closest — correct
- air
- empty space
- there is no air between them to carry the sound — correct
- helmets are soundproof
- it is too cold for sound
- soft, spongy materials that ABSORB sound — correct
- hard steel plates that reflect it back and forth
- mirrors