At-Home STEM Activities: Fun with Vibrations
Have you ever turned the music up so loud that you can feel it? The floor seems to hum, and you can feel the vibrations in the walls and other objects in the room. How can music travel from a speakers and cause such powerful vibrations in other objects? Before we explore this question, we must answer, what is a vibration? Vibrations are back-and-forth motions around a stationary position. In every case of a vibration, it begins with an object at a resting position, and the motion made by the object is in a back-and-forth nature over the resting position. When an object vibrates, it exhibits a motion that repeats itself over and over again in the same fashion.
Sound waves are created by vibrating objects that bump into adjacent air molecules. These air molecules bump into other nearby air molecules and so on, transmitting the vibration through the air to our ears. Sometimes these vibrations are easy to see, for example, when you pluck a rubber band, but most times the vibrations are too small or too fast for us to see, like when you knock on a door, it makes a sound even though you can’t see the door vibrate!
Your eardrums are tiny membranes inside your ears. When vibrating air molecules hit the membrane they cause it to vibrate. These vibrations are converted into electrical signals that are sent to your brain. In this activity you will make a model of your eardrum, and watch how sounds can make it vibrate! You will explore how sound creates vibrations and how that will affect small objects, from as little as a humming sound, to as loud of playing music through a speaker.
What you will need:
A Cookie Sheet
Plastic Wrap
Bowl
Sprinkles, Rice (salt will work as well, but is harder to see)
Wrap the plastic wrap around the bowl. If you need, pull a rubber band around the bowl to keep the plastic wrap in place, do so. The plastic wrap is like your eardrum, stretched over the bowl (your ear).
2. Bring your lips close to the edge of the bowl without touching it and hum loudly. Watch the plastic wrap closely. Does anything happen? Now, add some sprinkles to the top of the plastic wrap. Try to hum again. What happens now? if nothing happens, try humming louder or changing your tone. If your sprinkles fall off the bowl, add more. Try switching up what you put on the top of your bowl.
3. Music from a speaker is louder than humming. If you can, try to put a speaker up to your bowl and see what happens. If you don’t have a speaker, check out the video below to see how loud music effects rice.
Were you able to make the sprinkles dance? When you hummed loudly enough and at the right pitch, the sound waves generated by your voice should have made the membrane vibrate. The vibrations of the clear plastic wrap, however, are hard to see. After you added sprinkles the vibrating membrane made them bounce up and down so the vibrations were much easier to see.
Depending on the size, shape and material of the container you used, you might have had to adjust the pitch of your humming to get the sprinkles to dance. If your pitch was too high or too low, the sprinkles might not have moved at all; if you got the pitch “just right,” they may have bounced around like crazy and even fallen off the bowl. The way an object responds to sounds of different pitches is called its frequency response. Frequency is measured in hertz (Hz), or the number of sound waves per second. Human hearing typically has a range from about 20 to 20,000 Hz, meaning frequencies in that range will cause your eardrum to vibrate. Some animals, such as dogs, can hear much higher frequencies, up to about 45,000 Hz. That means, unlike humans, their eardrums are sensitive to vibrations at higher frequencies. That’s why dogs can hear “dog whistles” but we can’t!
