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Name: Kasey O.
Status: student
Age: 20s
Location: N/A
Country: N/A
Date: 2001-2002


Question:
I found this web site when I searched for "air resistance" on the web. I was wondering if you had any information that would be helpful for me in my Physics Class. It is an education class for middle childhood and my group is doing a project on air resistance and gravity. Anything you might be able to help with would be appreciated.


Replies:
Kasey,

The basis of air resistance is "pushing air molecules out of the way". The faster an object moves, the more molecules have to be pushed out of the way every second. This is why air resistance force is proportional to the speed of the moving object. I recommend giving a real-life picture of what is going on. Running through waist-high water is much more difficult than walking through it. The principle is the same, but there are not nearly as many air molecules to push out of the way.

Dr. Ken Mellendorf
Physics Instructor
Illinois Central College


Hi, Kasey !!

Well, I am sure that you can find a lot of experiments to make for your Class. I would like to suggest you the following :

1 - you get a small vessel (with about 5 liters) fill it with water, make 3 holes at the same distance from the water level ( say 5, 10 and 15 cm ) and light the top of the water level. The experiment must be conducted at a dark place. What happens ? Well, you will see three streams of water illuminated as an optic fiber. Here you can explain the parabolic path of water ( due to gravity and total reflection).

2 - If it is possible for you to get a vacuum ( I dont believe you have this possibility... ) in a glass tube, you could try to show them that a feather falls as fast a paper ball.

3 - another easy and ( I think ) interesting experiment would be : in a corner of a table you lay down a ruler ( of about 50 cm long ). In both ends of the ruler you put two small objects ( say, at the "zero" and at the "50 cm" you put a piece of rubber, or whatever ). Then, with a pulse, you push horizontally one of the objects. One will travel in a parabolic curve and the other falls in a straight path to the floor. Both will reach the floor at the same time ( you can hear it !! ).

4 - if you let me, there is another experiment very interesting that you can do : to blow ( with the mouth ) a strip of paper ( say, 30 cm length x 3 cm width ). If you blow the upper side, the strip will tend to go up, due to the greater air speed ( bigger speed lessens the pressure over the strip, so that the paper will be lifted ). Well, that has not too much to do with your desire, but...anyway, it may be useful in another occasion.

Best regards

Alcir Grohmann



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