Mass of fire, Speed of sight  

Q:  In my science class we have learned about mass, and I'm just wondering, does fire have any mass? It has stumped all the teachers I asked (even my science teacher), and I would really like to know.  (Jimmy, Sioux City, Iowa)

A:  Fire is a series of actions and changes that produces a result — a process.  In fact, it is an oxidation process (called combustion or burning) that gives out heat and light energy as well as glowing gas and a small amount of plasma. 

The flame color depends on the temperature of the hot burning gasses and the material that burns. Courtesy of the US Forest Service and Wikipedia

So, talking about fire's mass is like talking about the mass of digestion, or boiling, or getting a driver's license — although it certainly makes us think about what fire is.  But a process doesn't have mass.

Flames are another matter.  They are burning gases and gasses certainly do have mass.

Further Reading:

Flame colors as chemical indicators by Rod Nave, HyperPhysics

Fire, Wikipedia

Q:  I heard at 100 mph what seems to be in front of you is actually behind you because of how fast your eyes receives images. Is this true, and if so how? What speed can your eyes keep up with?  (Joe, Virginia Beach, Virginia)

A: Our eyes see faster than you think they do.  The entire process — from light entering the eye to the brain perceiving the image — takes a mere 50 milliseconds (one sixth of an eye blink).  See WonderQuest's speed of human sight. 

A pilot weaves among pylons in the Red Bull Air Race at Kemble Airfield, England. Courtesy of Red Bull Air Race and Wikipedia.

Fifty milliseconds isn't much time, but it is time.  So no matter how slowly you go, you will travel some distance during that time.  At 100 mph (160 km/h), you'll cover 7 feet (2 m).  At any speed, your side peripheral vision will pick up objects that are actually behind you.  How much difference does that make?  Not much.  In fact, not much even going 300 mph (480 km/h).

"We reach speeds up to 300 mph (when entering the track)," says Kirby Chambliss, aerobatic champion and winner of the 2006 Red Bull Air Race.  "The only time I have trouble seeing the pylons is when I am pulling 11 to 12 G due to tunnel vision.  If you are on a straight part of the track it is no problem to see the pylons even at 300 mph."  Video of the race.  

"...if we focus or try to see the pylons as we go through them [at speeds of about 200 mph (320 km/h)], they would actually be behind us by the time our brain could return a control input," says Mike Mangold, 2005 RBAR world champion.  "As I approach a gate, I position my aircraft to fly through what I perceive to be the center of the gate.  I do not see the pylons as I go in between them because I am already looking ahead to the next computation.  If I look too far ahead, then my ability to accurately position my airplane degrades."  Mike looks about one second ahead, which is approximately 300 feet (90 m).

Kirby and Mike travel up to 35 feet (10 m) during 50 milliseconds, and can judge distances ahead well enough that a 35-foot discrepancy doesn't matter.  What speed your eyes can keep up with depends on how accurately you need to know your position. 

Further Reading:

Mike Mangold Air Displays

Red Bull Edge, Kirby Chambliss, 5X US Acrobat champion

Red Bull Air Race

To see, brain assembles sketch images eyes feed it, University of California, Berkeley, UniSci

Colors are composed by brain not eyes, Cornell University:

(Answered April 18, 2006)