Supporting Science in Hong Kong Schools
Spring 2007
19
Smelly Science – What Makes Us Fart?
Living with Science; Life in Science
By Florence, LI Wing Huen
This article is intended for students of
Form Four or above
with background of Biology
Introduction
Sometimes it is really embarrassing if you fart in social occasions such as
a meeting, dinner party. Despite the “exploding” sound produced
from farting, fart smells make people around you keep their distance.
This article will give scientific explanations on this embarrassing
phenomenon. What actually makes us fart?
Cause of farting
Everyone should have had the experience of farting. Even a 3-year-old
kid can tell immediately that a fart is the gas erupted out of the anus.
So where does such gas come from?
Figure 1. The Human Digestive System
© Li Wing Huen 2006
Supporting Science in Hong Kong Schools
Spring 2007
20
Living with Science; Life in Science
When you eat, the food in your mouth will pass along your digestive
tract for digestion and absorption (Figure 1). Stomach is the main site
of digestion where most food will be digested1. However, certain
kinds of food like beans contain plenty of sugary chemical which is
difficult for digestion1. These foods will then enter the large intestine1,
where lots of small microorganisms called bacteria are situated there2.
The bacteria in your large intestine cause no harm to your body and
they even help the digestion of foods that are hard to digest1. The
bacteria will break down such foods into small particles by a process
called fermentation, in which different types of gases are produced2.
The food broken down will be absorbed in the large intestine, but
the gases produced will not2. As a result, the gases are accumulated
and finally erupted out of the anus as a fart.
Why fart produces sound?
“Bwuueee…”. The sound of a fart can sometimes be exaggerated in
cartoons. Such a sound of a fart is made from the vibra