Question Answered by Dr. Steven Shropshire, Physics Professor, Idaho State University
Yes, sound can travel right through you. While some sound is absorbed by your body, all sound waves can pass through you if they are loud enough. Sound is a vibration. It can be a vibration in the air, in water, and even in metal. Doctors use very fast vibrations called “ultrasound” to image what is going on inside of you. We can even make pictures of your insides from the echoes (reflections) of this sound from inside you. Most “pictures” you see of babies inside their mothers are made this way.
Our ears are only sensitive to a small range of sounds. There are sounds too low in pitch or “frequency” for us to hear. We call this “infrasound”, and it comes from vibrations less frequent than 20 cycles, or vibrations, per second. While we cannot hear infrasound with our ears, if it is loud enough we can feel it. We also cannot hear sound with vibrations more frequent than 20,000 cycles, or vibrations, per second. Sound in this range is called ultrasound.
We tend to think of a sound wave as something that travels through the air. After all, we can hear each other when we speak across long distances in the air, but not when speaking to someone separated by a wall or another object.
In reality, sound is passed from molecule to molecule, and it travels through liquids better than gasses, and through solids better than in liquids. This is because the molecules in a solid are closer together and can easily pass the sound wave along.
These experiments are designed to test whether the human ear can hear sounds through gas, liquid and solid.
Materials: balloon, 2 paper or plastic cups, scissors, string, tape, a bucket filled with water, large soda bottle, 2 big spoons, a friend
Experiment 1: Sound travels through a gas
- Blow up the balloon so it is filled with air (a gas).
- Hold the balloon up to your ear.
- Lightly tap the other side of the balloon with your finger. Can you year the sound well? Can you feel the vibration?
Experiment 2: Sound travels through a solid
- Using the point of the scissors, poke a hole in the middle of the bottom of each cup. (Depending on your age, it may be better to have an adult do this step.)
- Stand a few feet away from a friend and talk to each other in normal (not yelling) voices. Keep moving apart until you can no longer hear each other well enough to have a conversation.
- Hold one of the cups up to your mouth and speak into it while your friend listens into the other. Now can you hear each other?
- Next cut a length of string long enough to stretch between you and your friend at the distance when you could no longer talk to each other.
- Poke the ends of the string through the holes in the bottoms of the cups (poke it upwards through the bottom) and tape the ends securely to these bottoms.
- Hold onto one cup and have your friend hold onto the other and walk away until the string is taut (pulled straight, not sagging).
- Talk into one cup while your friend holds the other cup over her ear. (Remember to keep the string taut.) Switch. Could you hear best when sound traveled through air or through a solid (the string)?
Experiment 3: Sound travels through water
- After filling the bucket with water, take a sharp knife or kitchen shears to cut off the bottom of the plastic water bottle. (Depending on your age, it may be better to have an adult do this step.) Be sure that the cap is taken off of the bottle.
- Place the bottle in the water so that the cut bottom is in the water. Put your ear to the top of the bottle to listen.
- Have your friend clang the big spoons together to make a sound in the water bucket as you are listening. What do you hear? The sound of the clanging is loud and clear. Water travels faster through water than in the air.