Re: Experiment to be made at home on aquaplaning

Greetings:

Simple experiments to demonstrate physical effects are a wonderful teaching 
tool and often new ideas and applications come to mind while conducting 
these simple experiments. Measuring the static coefficient of friction of 
materials by  sliding them on inclined planes is a well known experiment 
However, aquaplaning, which is technically called  hydroplaning, is a 
dynamic effect related to rolling friction and is a bit more difficult to 
demonstrate. The demonstration would be a valuable teaching tool even for 
driver training courses! The following simple experiment demonstrates the 
effect by replacing water with air. 

EXPERIMENT MATERIALS

A piece of stiff cardboard or poster board, 10 cm by 10 cm 
(4 inches by 4 inches)
A small wooden or plastic sewing thread spool
A plastic soft drink (soda) straw
A balloon and a rubber band to tie the balloon’s neck.
All purpose glue and perhaps a cotton pad

EXPERIMENTAL SET UP

Cut out a 10cm (4 inch) diameter cardboard disk.

Punch or drill a small, tight fitting hole for the straw through the center 
or the disk.

Cut the thread spool in half and glue the large diameter end of the spool 
half to the center of the cardboard disk so that the holes are aligned.

Place the cardboard disk on a flat surface and insert the straw through the 
spool and disk holes keeping the end of the straw flat with the disk 
surface. Use cotton or glue to tightly lock the straw inside of the spool 
hole.


                _____
               /     \
              /       \
              I       I  -- BALLOON
              \       /
               \     /
                II II
                II II  -- BALLOON TIED TO STRAW
                 I I 
                 I I
                 I I  --- STRAW
                 I I
                 I I
              ___I I___
              I  I I  I
              I  I I  I -- HALF SPOOL GLUED TO CARDBOARD
              I  I I  I
       ______II__I I__II______
      I__________I I__________I -- CARDBOARD DISK

EXPERIMENTS

(1) Set the disk on a large flat table and snap the spool sideways. The 
disk will move a few centimeters/inches and friction with the table top 
will quickly stop the movement. This simulates car tires stopping on a dry 
smooth road.

(2) Blow up the balloon and while pinching the neck attach it to the straw 
with a rubberband. (This often takes 3 hands!)

(3) Set the balloon on the flat surface and then let the air pass through 
the straw  and the escaping air will lift the disk. Flick it and the disk 
will shoot across the table top on an almost frictionless cushion of air.
This is the same effect as hydroplaning with an air layer replacing the 
water layer trapped under the tires of a speeding car. This also 
illustrates the principle of a hover craft of the type used to quickly 
carry passengers and cars across the English Channel.

Here in California we cut grooves in the freeway surfaces to reduce 
hydroplaning on hills. The groves give the compressed water layer under the 
speeding tires a place to escape destroying the low friction water layer. 
You could cut groves in a large flat board to demonstrate this with the air 
model.

    
Best regards, Your Mad Scientist
Adrian Popa