Ask A Scientist© Physics Archive

name         Max
status       student
age          9

Question -   I am doing a project for the science fair at my >> 
school.  My problem is how does a the size of a soccer ball affect how >> 
far it goes when it is kicked.  What kind of science should I go to for >> 
my research and information?
------------------------------------------------
Hello,

The size (and thus also the weight) of the ball affect how far it goes.

To shoot a ball, you give it some energy. If the ball is lighter, it will 
start at a higher velocity and end up going further. Therefore, if made of 
the same material, a small ball is lighter and will go further.

An equally important factor is the air drag, that is, the resistance of air 
as the ball moves. You can experience air drag by holding your hand 
slightly (not too far, dangerous!) out of a moving car window and feel the 
drag force.  This force is also increases with size (and with velocity).

So, in a simple way, we say that both air drag and weight of a hallow ball 
are proportional to the radius of the ball squared.  So, if one ball is 10 
cm and another is 5 cm in radius, the weight and air drag on the bigger one 
are each 4 times those of the smaller one.
You can look up information on this topic in basic physics books, and also 
in books on dynamics and fluid mechanics.  An encyclopedia for young 
scientists also may be a good start.
By the way, you can make some interesting observations by dropping balls 
(metal or others) in a tall column of water (with or without a starting 
kick), or by blowing a fan on balls of different size and materials.  A 
stop watch and tape measure to measure time and distance traveled will you 
give some interesting insight.
You will need some assistance from your parents and teachers to try some of 
these ideas.

Good Luck,


Dr. Ali Khounsary
Advanced Photon Source
Argonne National Laboratory
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