Global Warming: Man or Myth?

Scientists can also wear their citizen hats

No, This Weather Really Blows

with 23 comments

I have been teaching introductory meteorology and climatology courses for 23 years.  Read on for the most common misconceptions that my students have regarding science:

 

1)      Draining water spins differently in the Southern Hemisphere than in the Northern Hemisphere

It is true that there is an apparent force caused by the earth’s rotation called the Coriolis Force or Coriolis Effect that does cause rotation in large high and low pressure systems.  It is also true that these large rotating systems spin differently in each hemisphere (low pressure systems spin counter-clockwise in the NH while spinning clockwise in the SH).

What is NOT TRUE is that the Coriolis Force causes rotation in a sink or toilet bowl.  The earth can only rotate an object once per day.  Any body rotating much faster than once per day has forces that dwarf the Coriolis Force.  Water draining in a sink certainly spins at a much higher rate than once per day.  In reality, draining water can spin in either direction in either hemisphere.  Flushing toilets are a particularly bad example because the water there is forced in a specific direction by the jets underneath the rim!

For more information please see the excellent explanation titled Bad Coriolis from a former graduate professor of mine at Penn State.

2)      Rubber tires keep you safe in your car from lightning strikes

It is true that one is relatively safe in the car from lightning strikes.  However, the tires are NOT the reason.  Surprising to most is that the metal frame of the car actually keeps the occupants safe inside!

Electricity will flow along the surface of conductive objects such as metal or water.  This is known as the skin effect or Faraday cage effect.  That means that the lightning will flow along the outside of the car and eventually into the ground.  This is why one should never step outside a car with a live power line touching the vehicle and one should avoid touching anything inside the cabin that may be connected to the outside such as door handles, radios, shifters, etc.  Rubber tires offer much less resistance to lightning than the atmosphere it is passing through so if the lightning bolt can overcome the air, tires are a piece of cake!

Watch a car get struck by lightning!

 

3)      Heat lightning is caused by hot, humid summer evenings

It is true that hot, humid conditions are favorable for thunderstorms.  It is also true that lightning is caused by a thunderstorm.  However,  hot, humid air itself cannot generate lightning and there is no such thing as heat lightning!

When a lightning bolt passes through the air, it rapidly heats that air which causes the air to expand.  The rapid expansion generates a sound wave known as thunder.  Light travels 186,000 miles per second while the slow poke known as sound only travels at 1/5 miles per second.  (As an aside: if one sees lightning and then counts the seconds until hearing thunder, every five seconds equals one mile of distance between the observer and the lightning.)  Because of its tremendous speed, light from lightning can travel very far and very fast and is easily seen many miles away.  However, sound may never reach one’s ears.  The result is visible lightning but no audible thunder or what many people would call “heat lightning.”

4)      It is only possible to balance an egg on the fall or spring equinox

Many people believe that on two days of the year (fall and spring equinox) the earth has no tilt and one can balance an egg.  If one can balance an egg on the equinox, then one can balance an egg on any day!  The earth’s “tilt” is 23.5 degrees every day of the year.  Contrary to myth, the earth does not “lose its tilt” on these two days.  The equinox is special because every location on earth gets 12 hours of day and 12 hours of night.  That’s it!

Visit this link to avoid getting egg on your face!

5)      Low pressure sucks air into its center

Wind is caused by various horizontal forces.  One such force known as the pressure gradient force (PGF) causes air to move away from higher pressure and toward lower pressure in an attempt to equalize horizontal air pressure differences.  Simply put, higher pressure systems are blowing air outward.  Lower pressure systems are not sucking the air inward.

Moral of the story:

If somebody tells you “this weather really sucks”, you need to correct them by saying “no, this weather really blows.”

About these ads

Written by Scott Mandia

July 12, 2010 at 6:00 am

Posted in Uncategorized

23 Responses

Subscribe to comments with RSS.

  1. Nice right up. I have to admit, I would’ve got the first one wrong – although I knew you could cause water to spin either way by acting upon it, I thought natural tendency fitted the Coriolis Effect.
    I’d never heard of number 4 – that seems really odd. :)

    mothincarnate

    July 12, 2010 at 6:26 am

  2. Nice Top Gear video. A good example of doing something that *seems* incredibly dangerous but which *ought* to not be, given our knowledge of electricity. I bet I’d feel pretty tense in the leadup too.

    Byron Smith

    July 12, 2010 at 9:31 am

  3. You’ve correct 3 out of 5 for me: tires and lighting; heat lighting; and blowing vs pulling air. Your comment on myth 5 troubles me. I had thought the main driver of wind was low pressure. An example from my region (southern California): deserts warm during the day, which sends hot air upward, and pulls ocean air toward it. I have a little trouble letting go of what I believed on this.

    jg

    jg

    July 12, 2010 at 9:37 am

    • jg,

      Yes, heating and rising of the air causes lower pressure but it does not “pull” air into it. The cooler, denser Pacific air blows into the lower pressure region. This is the same “sea breeze” mechanism that causes the Indian Monsoon.

      Wind is driven by pressure differences whether that difference is being caused by increasing or decreasing air pressure.

      Scott Mandia

      July 12, 2010 at 9:54 am

      • Thank you. To borrow from Webster’s speach, you can’t pull a rope of air. This image helps me.
        jg

        jg

        July 12, 2010 at 1:11 pm

  4. I’m from the “Volts can hurt but Amps can kill” school of thought, based on my electronics training over the years. Since there are an unlimited amount of variables in each instance, these figures are only an average.

    Static Electricity: 25-30K Volts/.002Amps
    Lightning Strikes: 30M Volts/100K Amps
    Stun Guns & Tasers: 250-400K Volts/.003Amps
    Electric Chair: 2K Volts/10 Amps
    Example Auto Video: 800K Volts/Amps unknown

    Then why do people survive lightning strikes? Variables…

    Jim "Zak" Szakmary

    July 12, 2010 at 11:35 am

  5. Of course the one-mile per 5 seconds distance from the lightning strike to you may be 5280′ straight up!

    Tim Warner

    July 13, 2010 at 4:34 pm

  6. Your inclusion of myth #5 really bugs me.

    It sounds like you are saying the air movement result from repulsive collisions from higher concentrations of air molecules rather than an attractive force from a lower concentration of air molecules. But this situation is exactly what the word suck was made to describe. My mouth sucks air through a straw. My vacuum cleaner sucks air into a hose. My child sucks her thumb. What’s left that suck can apply to? Attractive forces like electromagnetism and gravity?

    The word suck derives from an Old English word “sucan”. I bet the Old English didn’t have electrostatic attraction in mind when they were complaining that the Normans sucked.

    SuzieNeunmalKlug

    July 13, 2010 at 4:54 pm

    • It is much simpler than that. The PGF is a result of gravity. Imagine two tubes of water with unequal heights of water connected by a horizontal tube. Gravity will cause the water levels to equalize which means there will be a horizontal force pushing water away from the higher column of water toward the lower column until the two water columns are equalized.

      Scott Mandia

      July 13, 2010 at 6:16 pm

  7. I’m sorry, but you’re just wrong about the Coriolis effect.

    The Coriolis effect does not determine the direction of rotation of the water in a toilet bowl, but that is not because the water rotates faster than once per day. The speed is not really relevant — You are misstating the actual physical principle.

    There are many other influences acting on the water in a toilet bowl (shape of bowl, eddy currents, objects in bowl, shape of drain, etc.), and the Coriolis force is relatively small player. That’s why it doesn’t control the direction. If you could set up the experiment carefully and eliminate these other biases, you would see that the Coriolis force does control the rotation of the water. This can be demonstrated in the laboratory.

    Steve

    July 13, 2010 at 5:55 pm

    • Steve,

      I did simplify the CF so that it was easy to understand. The magnitude of the CF is so small that it takes much time for it to cause a displacement that is noticeable.

      The simplest way to explain this is the rotation rate of Earth vs. rotation rates of much faster rotating objects. As you state, other forces in a sink are many times larger than the CF so the CF is negligible.

      Recall I wrote: Any body rotating much faster than once per day has forces that dwarf the Coriolis Force.

      Effective communication often requires simplification and this blog is not for those with physics coursework. :)

      Scott Mandia

      July 13, 2010 at 6:27 pm

  8. Thanks for the article. But you! really! don’t have! to use exclamation! points! so much! Sorry…just a pet peeve of mine.

    TW

    July 13, 2010 at 5:57 pm

  9. Coming from the most lightning-strike state of Colorado, the counting of the seconds to judge where the strike is is not really being very clear. A bolt of lightning can stretch horizontally, creating the thunder, which could emanate from a point several miles away, or, just right above you.

    I think you ought to be clearer on this one.

    Tenmile

    July 13, 2010 at 10:51 pm

  10. [...] This post was Twitted by denbutsu [...]

    Twitted by denbutsu

    July 13, 2010 at 11:37 pm

  11. Sorry Tenmile, but Florida is easily in first place. Colorado is tenth, based on the lightning death rate. See NOAA Technical Memorandum NWS SR-193.

    Egg Roll

    July 14, 2010 at 2:39 am

  12. Does anyone know if the Faraday cage effect would work for a lightning strike on a convertible with the top down? Or perhaps with a soft top up – there are metal bars that support the frame of the cover.

    kevin

    July 14, 2010 at 9:29 am

  13. I understand that coriolis DOES cause the rotation we see in a tornado, or waterspout, or in ssome storm cells. Right or wrong? If wrong, what causes the violent rotation in a tornado?

    leeflyer

    July 14, 2010 at 2:11 pm

    • The CF does not cause the rotation in tornadoes and some tornadoes in the NH have been observed to spin clockwise. The rotation in tornadoes is caused by the PGF and centrifugal forces being in balance which is known as cyclostrophic balance. One way to imagine this is to recall what happens when an ice skater is rotating and pulls his/her arms inward. The rotation rate increases. When the skater’s arms are extended the rotation rate slows.

      Check out Rossby Number on Wiki to see when the CF is important.

      Scott Mandia

      July 14, 2010 at 2:56 pm

  14. [...] Global Warming: Man or Myth – via Boing Boing [...]

  15. Has there been a recorded incident of a hurricane, cyclone, or typhoon rotating in the ‘wrong’ direction for the hemisphere where it was located? Has one of these storms ever crossed the equator?

    catman306

    July 17, 2010 at 5:32 pm

    • Not that I am aware of. There cannot be a large rotating storm near the equator because the CF weakens to zero as a storm moves toward the equator. (CF is stronger at the Poles and zero at the equator.)

      A hurricane, if moving toward the equator, would end up losing its rotation and would become a large blob of unorganized thunderstorms so it would not “cross” the equator as a hurricane.

      Scott Mandia

      July 18, 2010 at 7:57 am

  16. Sorry but the Egg-Equinox answer is a bit incorrect. 12 hours day/night occurs 4-5 days before/after the Equinox because (as I know you know) of refraction and “time” of sunrise/sunset. Better would be to say that the Equinox is the date/day when the Sun rises exactly in the east and sets Exactly in the west (even with refraction). . .and BTW is not “offically” anything.

    RTR

    Mandia: You are correct and I was wrong. I do understand refraction but I never considered that aspect when describing the equinox. Your definition is much more appropriate. Thanks for the catch.

    bob ryan

    July 25, 2010 at 6:07 pm


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Follow

Get every new post delivered to your Inbox.

Join 3,351 other followers

%d bloggers like this: