Air Resistance Made Simple
Name: Susan J.
Date: April 2006
What is a simple definition of "air
resistance" for a second grader?
Here is a two part response, an answer and an experiment.
First, it is the force that the air exerts on an object moving through
it. A simple analogy is that of friction on a surface. Air resistance
is (more or less) the friction you get from moving through the air.
Now for experiments: The best thing I can think of is the old "hand out
the window of a moving car." At slow speeds there will be little
(perhaps not even noticeable) resistance. At higher speeds you will
feel the resistance of the air to the motion of your hand. By
presenting a large area (palm open to the wind) there will be more
resistance and by presenting your hand edge on there will be less
resistance. I think this is a great way for a child to actually
experience air resistance.
Now, if they want to "see" air resistance, I would suggest taking a trip to
a swimming pool. The sluggish motion we all experience while trying to
run through the water in the shallow end of the pool is very much the
same thing(though greatly increased!). Here they can actually see the
currents of the water as it flows around them and the whirlpools that
form from the motion.
Michael S. Pierce
Materials Science Division
Argonne National Laboratory
Although we cannot see it air has weight (actually mass, but skip
the difference). When we move through air, whether by running, on a
bicycle, or in a car, we have to push that air out of the way. The
faster we move the harder it is to move the air out of the way
because the faster we travel the more air we have to move every
second. So air resistance increases as we move faster -- walking
less than running less than a bicycle less than a car. You can feel
the air pushing against you more as your speed increases. The more
that air weighs the harder it is to push it out of the way. A good
analogy would be how hard it is to walk in a swimming pool than it
is to walk on the ground in the air. Water "weighs" more so it is
harder to move out of the way as we try to walk through it.
Hope this gives you some leads how to proceed.
At room temperature, air is a gas and water is a liquid. Both gases and
liquids have properties that classify them as "fluids".
Here is the definition of a "fluid": A continuous, amorphous substance
whose molecules move freely past one another and that has the tendency to
assume the shape of its container; a liquid or gas.
As objects move through fluids, the fluids have to move out of the way,
around the object. That is called "resistance". You can feel this
resistance when you push your hand in water -- it is easier to push your
hand through the water when you "slice" through the water compared to when
you paddle through the water (but in both cases you feel some resistance).
The same is true when you stick your hand out of the car window as your car
(and your hand) move through the fluid called air.
Second graders can compare which shapes (race cars vs. big trucks) and
discuss which are better designed to reduce air resistance and allow them to
I hope this helps!
Todd Clark, Office of Science
US Department of Energy
Perhaps you could describe it as the wind-like force you feel from
moving quickly. Although you wouldn't want to encourage a 2nd
grader to stick hands out windows of moving vehicles (at least not
more than a few inches), that might be something most have
felt. Another example might be riding on a bike, when there's no
wind out, it feels like there is a wind when there is none. That
force they feel, that seems like a wind blowing against the
direction they are moving. is air resistance.
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Update: June 2012