|I would like to know if air resistance will
decrease as an object's speed decreases and is
less for a smaller surface.
|Question Date: 2005-01-14|
That is a very good question! You've already
figured out the two things that most affect air
resistance or what engineers call "drag". The
force of the air pushing past an object in motion
is proportional to the object's frontal area times
the square of its velocity. (To understand what
frontal area is, imagine cutting a baseball in
half. The flat surface that you made when you cut
the ball is its frontal area or the area "seen" by
the air.)So you can see that velocity is the most
important variable. Let's say I throw a ball
through the air. Next, let's throw a ball that is
2 times as big. We have just increased the drag
by 2 times (if the drag force was 1,it is now 2).
Now, let's just throw the smaller ball 2 times as
fast. We have just increased the drag by 4 times
(if the drag force was 1, it is now4).
Air resistance is the number of molecules of air
that an object is hitting as it travels through
the air per unit of time. The faster you are
going, the farther you go in a given length of
time, and so the more air molecules are in your
way across that distance.Likewise, if you are
smaller, the fewer air molecules are in your way.
So, in other words, the answer is"yes" to both
Indeed it will. The larger the moving object, the
greater will be the resistance of air to its
motion. This is why racing cars are very slim and
low on the ground. As objects move faster, the air
resistance will increase. Very often, the
resistance increases as the square of the
velocity, so that an object traveling at 10 m/s
has a resistance that is four times larger than an
object traveling at 5 m/s.
The drag force, or the resistance of a medium to
the motion of objects in it, is proportional to
the square of the velocity and to the
Cross-sectional Area of the moving
Decreasing the speed will therefore
decrease air resistance and decreasing the surface
area will decrease air resistance..
most common method of mathematically modeling the
drag force is the equation, FD=0.5CD*Arv^2.
= Drag Force. .
CD = Drag Coefficient. .
= Cross-sectional Area perpendicular to the flow.
r = Density of the medium. .
v = Velocity
of the body relative to the medium.
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