Cumberland Times-News

Bob Doyle - Astronomy

July 7, 2012

This is science you can use every day

There’s an interesting new book that shows how science can be helpful in our everyday lives. “Better Living Through Science” by Mark Frary was published by Modern Books in 2011 (from the U.K.) and has ISBN 978-1-906761-32-5.

I’ve decided to take up the items in this book that relate to automobiles.

This book goes into other topics such as moving sofas around corridors, saving on your electricity bill, winning at cards, Scrabble, ways of getting a lid off a jar, sailing a yacht, etc.

Even though most of us are now annoyed with our summer heat, a winter problem is removing ice from our car windshield. What’s the easiest way to avoid this problem or remove the ice most easily?

An easy way to avoid ice is to put a small tarp or piece of heavy plastic over our windshields, fastening it by using the windshield wipers or inserting the ends in the side windows. (Of course, if there are strong gusts, the tarp or plastic might be blown off.)

If the ice is on the windshield, the author suggests making a deicer solution of 3 parts white vinegar and one part water. You then put the solution in a spray bottle and then squirt it on your windshield.

 Commercial deicer sprays from auto parts stores contain methanol which freezes at -143 F.

Now with gas or diesel fuels prices at a high level, how can one go the farthest on a gallon of fuel? On a level road, there are three horizontal forces acting on a car.

There’s air resistance, the rolling resistance between the tires and the road force (that pushes the car forward). The air resistance or drag depends on the car velocity squared, the drag coefficient and the cross sectional area.

So the faster you drive, the more the air resistance. A car driven at 75 miles an hour has 56 percent more air resistance than the same car driven at 60 miles an hour.

The drag coefficient varies quite a bit; a Prius has a coefficient of 0.25, a Hummer2 has 0.57, compared to a brick of 2.1.

Of course the bigger the cross section, the more the drag. This gives a low slung sports car quite an advantage over a relatively rectangular SUV.

The rolling resistance is minimized if the tires are properly inflated. Of course, over inflated tires will wear in the center of the treads.

Under inflated tires increase the rolling resistance as more of the tire is in contact with the road.

The road force is a reaction force. As the tires roll, they push back on the road.

The road to retaliate, pushes the tires (and car) forward. This is an example of Newton’s third law.

To walk forward, we push back on the ground or floor; the ground or floor pushes us forward!

Another way to go further on a gallon of fuel is to minimize the weight of the vehicle.

Reducing the stuff in your trunk is helpful. Smooth acceleration also saves fuel, compared to rapid and jerky acceleration.

If you have a manual transmission, shift to the next gear as soon as possible to save gas.

“Better Living Through Science” has a very nice treatment of stopping distance for automobiles.

A good rule is that your reaction or ‘thinking’ distance grows 10 feet for every multiple of 10 miles an hour.

So your reaction distance is 10 ft. at 10 miles/hour, it will be 40 feet at 40 miles an hour.

 Then you must add the actual braking distance to the reaction distance. At 20 miles per hour, the braking distance is 20 feet.

This means a total distance of 40 feet is needed to stop your vehicle at 20 miles an hour.

Consider driving at 40 miles/hour, there is a reaction distance of 40 feet. The braking distance is then 80 feet or four times as much at 20 miles/hour.

This results in a total distance needed to stop of 120 feet.

At 60 miles/hour, the reaction distance is 60 feet. The actual braking distance grows to 180 feet. So the total distance to stop would be 240 feet.

SKY SIGHTS THIS WEEK: At dawn tomorrow, the brilliant planet Venus will appear close to Aldebaran, the bright orange star marking Taurus’ eye. On Wednesday morning, the moon will appear half full in the southern dawn.

Even after the sun rises, you can spot some of the moon’s larger craters along the moon’s right edge with binoculars.

This coming Friday, July 13 will be the third Friday the Thirteenth of this year. It is interesting that our three unlucky Fridays in 2012 are each separated by thirteen weeks.

Most years have one or two Friday, the Thirteenths. Three Friday the Thirteenths occur about 14 to 15 years per century.

Bob Doyle invites any readers comments and questions. E-mail him at rdoyle@frostburg.edu . He is available as a speaker on his column topics.

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Bob Doyle - Astronomy
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