What it shows
A funnel gathers the faint sound of the heart and the tube guides it to the ear, so a heartbeat sounds louder than it does through the air. You hear two sounds, lub and dub, made by the heart valves closing.
The science
Sound is a vibration, and in open air it spreads in all directions and becomes weak. A funnel collects the vibrations of a bigger area and the closed tube stops them from spreading, so more energy reaches the ear. The heart sounds come from the valves snapping shut: the first sound, lub, is the valves between upper and lower chambers closing, and the second, dub, is the exit valves closing.
Materials
Cost: under Rs 50. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A plastic funnel about 8 cm wide
- About 60 cm of clean soft rubber or plastic tube that fits the funnel stem
- A balloon or thin plastic sheet for a diaphragm
- A rubber band
- Cotton wool and spirit swabs for cleaning
- A notebook
Safety
For this project: An adult must cut the plastic and help with the tube. Clean the earpiece with a swab before another child uses it, and never hold the funnel hard against the chest.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Check the tube fits snugly over the funnel stem and trim it so that it is about 50 cm long.
Stretch a piece of balloon rubber tightly over the wide mouth of the funnel and fix it with a rubber band. The skin must be tight like a drum.
Place the open end of the tube lightly at your ear, with an adult holding it if the child is small.
Sit in a quiet room. Place the funnel on the left side of a friend’s chest, a little below the nipple level, and listen.
Count the beats for 30 seconds and double to get the rate. Compare with the matchstick pulse indicator.
Listen to the lub and dub and describe the rhythm with a drawing of a sound line in your notebook.
Try the funnel without the tube and without the diaphragm, and note which version is loudest.
Listen to breathing sounds on the back of the chest as well, comparing the sounds of breathing in and out.
What you should see
You hear a steady lub-dub, about 70 to 90 times a minute at rest, which is louder than with the bare ear, and louder with the balloon skin than without it.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Why does the tube make the sound louder?
It keeps the sound waves inside the tube so they do not spread out and fade.
2What makes lub and dub?
The heart valves closing one after the other.
3What is the use of a stretched diaphragm?
It vibrates with the sound and passes it into the funnel.
4Why should the room be quiet?
Noise from outside travels in the tube too and hides the faint heart sounds.
Take it further
Measure the heart rate of a sleeping dog or cat with an adult’s help and compare it with a human.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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