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« of science and superheroes | Main | food for juicy, young brains »


Early automobiles all had natural rubber, solid white tires. Which was not a big issue when 15 MPH was a typical cruising speed. You can still get all white automobile tires (scroll down to bottom of the page, on the lower right), but they are mostly for pre-1920 classic car restoration.

White wall tires, which today are made with artificial pigments, were originally made with vulcanized rubber for the tread and natural rubber for the sidewalls. The style stuck, because the styling suggested the gravitas and luxury of cars like President Taft's steamer in the first link above.

Wow. That covered a lot of topics! Its honestly not something I had ever thought about. I did think about the fact that tires give of black smoke when they are actually burned which contrasts nicely with the white smoke you described.

The carbon black filler also serves another purpose. Rubber is naturally an electrical insulator. However, in the process of driving, static electrical charges may be deposited on the body of the automobile. If these charges are not safely drained off, electrical discharges may occur. If this happens to happen while refueling the vehicle, the results can be explosive. Fortunately, though, the addition of the carbon black adds a bit of conductivity to the tires, which allows the static charges to be safely dissipated, so that your car doesn't turn into a torch while filling it with gasoline.


I like the title. Steal one of them good ol' country tunes for it and I think you've got a hit.

BTW, people might wonder what happens to the rubber that used to be their tire treads, when they don't perform the kind of maneuvers that leave skid marks or make smoke. The answer is, "You're breathing it."

The particles that get rubbed off your tires in normal use are small enough to float in the air for on the order of an hour. They tend to be smaller than a wavelength of light, but not much smaller. As a result, they "forward scatter," that is, they change the direction of light by a small amount, but don't bounce it off at right angles.

I used to work with Fred Voltz, who had the longest and most extensive series of atmospheric aerosol measurements. He found that aerosols in this size range peaked during morning and evening rush hour. He did his measurements several miles from the nearest major highway, so the rubber particles had to drift quite a ways to reach him.

"In fact the size of a typical molecule is comparable to UV light."

No, Typical gas molecules are a few Angstroms across - that's X-rays, not UV.

Bob, you're right. I can only wonder what the insides of Jimmie Johnson's lungs look like at this point. I have a meeting with some tire designers about so-called eco-friendly tires and I will ask what they are doing in terms of particulate contamination. Nice point.

Tim - ugh. Yes. I am teaching a seminar on x-ray interactions with materials and got myself confused there. Thanks!


Peat is does appear that someone has shaved their legs...Good observation...Being unfamiliar with this process, I looked it up on Wikipedia and the definition is: "It is a very common practice among women in Western countries

Extremely interesting post. I had heard that manufacturers simply "paint" tires black, which holds some truth I guess (a very simple explanation lol). Definitely hit on some things I would have never thought of. Thanks for the useful information.

@jeffery kegler

All the better reason to ride with my windows up on a hot day. Can you imagine all the rubber you could be inhaling on your commute to work?

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    Physics Cocktails

    • Heavy G
      The perfect pick-me-up when gravity gets you down.
      2 oz Tequila
      2 oz Triple sec
      2 oz Rose's sweetened lime juice
      7-Up or Sprite
      Mix tequila, triple sec and lime juice in a shaker and pour into a margarita glass. (Salted rim and ice are optional.) Top off with 7-Up/Sprite and let the weight of the world lift off your shoulders.
    • Listening to the Drums of Feynman
      The perfect nightcap after a long day struggling with QED equations.
      1 oz dark rum
      1/2 oz light rum
      1 oz Tia Maria
      2 oz light cream
      Crushed ice
      1/8 tsp ground nutmeg
      In a shaker half-filled with ice, combine the dark and light rum, Tia Maria, and cream. Shake well. Strain into an old fashioned glass almost filled with crushed ice. Dust with the nutmeg, and serve. Bongos optional.
    • Combustible Edison
      Electrify your friends with amazing pyrotechnics!
      2 oz brandy
      1 oz Campari
      1 oz fresh lemon juice
      Combine Campari and lemon juice in shaker filled with cracked ice. Shake and strain into chilled cocktail glass. Heat brandy in chafing dish, then ignite and pour into glass. Cocktail Go BOOM! Plus, Fire = Pretty!
    • Hiroshima Bomber
      Dr. Strangelove's drink of choice.
      3/4 Triple sec
      1/4 oz Bailey's Irish Cream
      2-3 drops Grenadine
      Fill shot glass 3/4 with Triple Sec. Layer Bailey's on top. Drop Grenadine in center of shot; it should billow up like a mushroom cloud. Remember to "duck and cover."
    • Mad Scientist
      Any mad scientist will tell you that flames make drinking more fun. What good is science if no one gets hurt?
      1 oz Midori melon liqueur
      1-1/2 oz sour mix
      1 splash soda water
      151 proof rum
      Mix melon liqueur, sour mix and soda water with ice in shaker. Shake and strain into martini glass. Top with rum and ignite. Try to take over the world.
    • Laser Beam
      Warning: may result in amplified stimulated emission.
      1 oz Southern Comfort
      1/2 oz Amaretto
      1/2 oz sloe gin
      1/2 oz vodka
      1/2 oz Triple sec
      7 oz orange juice
      Combine all liquor in a full glass of ice. Shake well. Garnish with orange and cherry. Serve to attractive target of choice.
    • Quantum Theory
      Guaranteed to collapse your wave function:
      3/4 oz Rum
      1/2 oz Strega
      1/4 oz Grand Marnier
      2 oz Pineapple juice
      Fill with Sweet and sour
      Pour rum, strega and Grand Marnier into a collins glass. Add pineapple and fill with sweet and sour. Sip until all the day's super-positioned states disappear.
    • The Black Hole
      So called because after one of these, you have already passed the event horizon of inebriation.
      1 oz. Kahlua
      1 oz. vodka
      .5 oz. Cointreau or Triple Sec
      .5 oz. dark rum
      .5 oz. Amaretto
      Pour into an old-fashioned glass over (scant) ice. Stir gently. Watch time slow.