On Monday morning, Steve received a call from NBC Nightly News from a producer who wanted to learn more about the science of walking on fire.
People can actually walk on hot coals… but the trick is understanding how heat is transferred from the hot coal to the person’s feet. Prior to the walk, someone lights the fire well ahead of time to allow the wood to burn down to non-flaming coals. The stunt is usually held at night. If it were done during daylight, the bed of coals would look instead like a bed of ashes. There is always a layer of ash covering the coals. By doing it at night, the glowing red light is still visible through this layer of ash.
Here’s the basic science… people are able to walk across a bed of burning coals because wood is not really a good conductor of heat. Basically, there’re three ways heat can get transmitted… conduction, convection, and radiation.
Conduction is the transfer of heat from one substance to another via direct contact. In convection heat is transferred through air or fluid circulation. In radiation it is transmitted as if spreading out in straight lines from a central source (think of the sun or a heat lamp).
Conduction is the main way heat is transmitted to a person’s feet during a fire walk.
In fire walking, the participant’s feet actually touch the ash-covered coals. However, if you were to pick up one of these pure-carbon coals, you would notice that it is extremely light, and this lightweight carbon structure is a poor conductor of heat.
It takes a relatively long time for heat to transfer from the glowing coal to your skin. It’s also important to know that ash is a great insulator that rests between the hot coals and the person’s skin. So, the ash covered coals transfer their heat even more slowly because the ash acts as a layer of insulation.
Bottom line… walking on coals is dangerous regardless of the theoretical science. According to our friend, David Willey, professor of physics with the University of Pittsburgh, most fire-walks occur on coals that measure about 1,000 degrees Fahrenheit (550 degrees Celsius), but he once recorded someone walking on 1,800-degree (1,000 °C) coals.
Believe it or not, sweat or moisture on the person’s feet can also help to provide a layer of protection due to a principle called the Leidenfrost Effect. The phenomenon explains how a small amount of moisture can produce an insulating vapor layer which keeps that liquid from boiling very quickly. Most people have watched what happens when drops of water fall into a very hot skillet – the drops quickly dance on the surface for a few seconds before finally vaporizing. If the skillet’s temperature is at or above the Leidenfrost point, the water quickly skirts across the pan and actually takes longer to evaporate that it would in a skillet that is above the boiling temperature but below the Leidenfrost point. This protective vapor barrier is what allows science demonstrators to pour liquid nitrogen on their hands or to quickly dip a finger into a pot of molten lead. Both practices are bad ideas no matter how much you believe in or understand the scientific principle behind the stunt. Don’t do it… but you’ll never look at drops dancing around a hot surface the same way again!
This is an encore posting from June, 2011 on 4th of July science activities. Many areas in Colorado have cancelled their fireworks displays this year due to extremely hot and dry conditions. Here are some ways to celebrate without fireworks or firecrackers…
Independence Day is the absolute best of summer – picnics, barbecue, fireworks and family fun. Are you looking for something to keep everyone entertained during your 4th of July summer picnic? We have some suggestions for summer learning fun…Fourth of July celebrations.
Before you watch the rockets red glare, how about firing off some of your own rockets, making your own ice cream and designing your own light show? Here are some of our recommendations to make your 4th of July barbecue sizzle.
Each year, an average of more than 75,000 wildfires burn an average of about 7 million acres of land in the United States.
– U.S. Forest Service
We are in the midst of one of the worst fire seasons in Colorado history and it’s still June. At present time, there are 10 major fires burning across the state. One, the Waldo Fire, is burning within the city limits of Colorado Springs. Another, the High Park fire, is burning near Fort Collins and has destroyed almost 250 homes.
So far this season, Colorado wildfires have burned acreage as big as the City and County of Denver. But what does it all mean? How do wildfires burn and grow? The fire in Colorado Springs grew from just over 6,000 acres on Tuesday to over 15,000 acres on Wednesday. Firefighters said there was a firestorm that pushed the fire to grow faster than expected.
Watch this timelapse video of the fire over five days. If you skip ahead to about 7:30 in the video, you can really see the firestorm and the weather system created by it.
A firestorm is a fire that is so intense that it creates and sustains its own wind system. A natural phenomenon, firestorms are created during some of the biggest wildfires. A firestorm is created as the heat of the fire draws in more and more surrounding air. If a low level Jet Stream exists near or over the fire, the air is drawn in even faster. As this occurs, strong, gusty winds develop around the fire, pulling the air inward supplying the fire with additional oxygen. The strong winds change direction erratically. The circulating wind can create fire tornadoes which quickly spread the fire to areas outside of the burning fire.
The firestorm continues to pull in great quantities of oxygen, increasing combustion and increasing the heat. The intense heat can ignite flammable material at a great distance ahead of the fire. This helps the fire grow quickly and increases the intensity.
People and animals near a firestorm can die from lack of oxygen.
Heat from the fire can melt asphalt, metal and glass.
Firestorms can also produce fire clouds which can produce lightning and spark new fires.
Like the Waldo Canyon fire on Tuesday, Wildfires can take on a life of their own, tearing over ridges, changing direction and fighting to survive.
A fire needs fuel to burn, air to supply oxygen and a heat source. This forms a fire triangle. When fighting a fire, firefighters work to take away one of the pillars of the triangle, they can control and put out the blaze.
The Spangler Effect recently covered fire tornadoes –
Weather also plays a huge part in wildfire birth, growth and death. Temperature, wind and moisture affect wildfires and make it harder to fight them. Drought obviously leads to favorable fire conditions. Moisture can slow the fire down. Wildfires tend to rage in the afternoon after sunlight heats sticks, trees and leaves on the ground. The radiant heat dries fuels and allows them to ignite to burn faster. Cooler temperatures help the fire lay down and give firefighters the upper hand in gaining control.
Wind has a huge impact on wildfires adding additional oxygen and pushing the fire faster. It is also unpredictable, changing a fire’s direction without warning.
More than 30,000 people are currently on evacuation orders north and south of Denver. The High Park fire is so big, firefighters are estimating it may take until the end of July to contain it.
What does it mean to contain a fire?
Control lines are constructed or natural barriers at the fire’s edge used to control a fire. Firefighters manually dig lines around the edges of a fire. The goal is to keep the fire from jumping the line and continuing to grow. Rivers and roads are also used as containment lines. Lines do not always work and fires can jump to continue burning. A fire can go from 50% contained to 30% contained if a fire line is jumped.
Strong winds can blow embers over 1/2 a mile and ignite spot fires out and beyond the main fire. This is very dangerous for firefighters as they can become trapped between the two burning fires.
Firefighters also set back fires. These fires are set to burn back towards the wildfire to create a burned zone and containment area.
How is containment measured?
Containment is estimated by the fire manager until a 100% containment is reached.
Wildfire Suppression Tools:
Modular Airborne Firefighting Systems that are inserted into military C-130 aircraft that converts them to large airtankers when needed. The C-130’s can drop up to 3,000 gallons of fire retardant on wildfires. The entire load can be dropped in under five seconds. The U.S. Forest Service has a total of eight MAFFS in its fleet.
Airtankers deliver fire retardant to slow the growth of wildfires and reduce their intensity to assist firefighters constructing containment lines on the ground. Wildfires are stopped by the containment lines. The fire inside the lines usually burns itself out.
Helicopters are also used to drop retardant or water to assist firefighting efforts on the ground.
What Happens During Mop Up Stage:
Mop-up happens after any part of a fire is controlled. It makes the fire safe by extinguishing fires and removing burning materials. Firefighters put out smoldering materials and make sure burning fuel is burned out or buried to stop sparks from traveling. They also clear fire lines of hanging branches, brush and logs to ensure the fire is contained.
Infrared scanners on helicopters or other aircraft are then used to detect hot spots to aide the mop up process.
A sequence of chemical reactions between a fuel and an oxidant. Heat and light are produced from the reactions in the form of flames or a glow. In rapid combustion large amounts of heat and light energy are released.
A technique used by forest service or firemen to burn excess fuels like grass or bush to prevent wildfires or restore grassland or forest ecology. Fires can stimulate germination of some forest trees and in turn promote a healthier ecosystem.
A wildfire that is so strong and intense, it creates it own winds.
Fire Tornado: Like a wind tornado but is made of fire. As the heated air from the fire rises, strong air currents (often whipping through the trees) cause the air molecules to spin (often referred to as angular or rotational momentum) which shapes the flame into the shape of a tornado. This catches the tops of trees on fire and the fire jumps from tree top to tree top.
An oxidizing agent is a substance that removes electrons from another reactant in a chemical reaction. The oxidizing agent is reduced by taking electrons and the reactant is oxidized by having it’s electrons taken away. Oxygen is an oxidizing agent.
Small particles suspended in air from an incomplete combustion of fuel.
A flameless form of combustion that gets its heat from oxidations on the surface of a fuel. Many materials can smolder – coal, tobacco, wood, fuels on the forest floor like peat and cotton clothing.
An out of control fire burning in wildland areas – also known as a forest fire, grass fire, brush fire, bushfire or vegetation fire.
Wildland Fire Suppression:
A type of fire fighting different than normal structure fire fighting. Wildfire crews work with firefighting aircraft to knock down flames, build a fireline and mop up hotspots.
For more information on the science wildfires, check out these great links:
Do you know how much sugar is in that can of soda you drink every afternoon? It’s well known that sugar accounts for the high calories in soda that lead to weight gain and unhealthy habits. But just how much is in that can and what about diet soda?
Start by placing different types and brands of soda into a bucket of water. Which ones will float and which ones will sink? Classify and take notes. Then move to the science behind your results. Why do some float and why do some sink?
Start with comparisons – we are going to use Coke and Diet Coke in our example. Both cans are the same size and hold the same volume 355 mL. The regular Coke weighs about 384 grams while the Diet Coke weighs 371 grams. The regular Coke has 140 calories, the diet Coke has zero calories. Are the calories the thing that makes it weigh more? Sort of.
The regular Coke has 39 grams of sugar. But what does that mean? About 18 packets of sugar in one can of regular Coke.
The reason the regular Coke sinks is the sugar content. If you drank one can of soda every day for a year, you would consume 32 pounds of sugar!
For more on the Science of Sugar, watch this week’s episode of The Spangler Effect where Steve goes beyond the sugar in a can of soda and makes some very sweet discoveries.
This is an encore posting of an article we ran in spring of 2010 about balancing an egg on the equinox.
The first day of spring and the vernal equinox is this week. The vernal equinox marks the start of spring, an autumnal equinox marks the start of fall. During the spring and fall equinox, the sun is directly over the Earth’s equator and day and night lengths are equal for most of the planet – 12 hours of light and 12 hours of darkness.
The earth rotates around the sun on a tilted axis, which doesn’t change. When the Northern Hemisphere is tilted toward the sun, it experiences warmer, longer days. When the Northern Hemisphere tilts toward the sun, the Southern Hemisphere is tilted away, experiencing colder and shorter days.
As the earth continues on its path around the sun, there are two points at which the sun hits the Earth perpendicular to the axis. When the earth is in this position, the sun is directly over the equator and there is an equinox. The earth then continues to tilt the opposite side of the sun and the seasons change to winter in the Northern Hemisphere and summer in the Southern Hemisphere.
Where we live in the Northern Hemisphere, the vernal equinox signals the start of spring. The North Pole is tilted toward the sun and days grow longer and warmer while buds on trees and plants begin to sprout. In the Southern Hemisphere, the opposite is occurring. The South Pole tilts away from the sun and the days grow shorter and cooler.
It is believed that during the equinox an egg can balance on end. This is more myth than science, but every year during the equinox, this question arises. Yes, with a little patience you can balance an egg on end during the equinox.
What will happen if you try to balance the egg on March 21st? Or April 20th? Or October 2nd? The egg will balance the same on any day as it does on the vernal or autumnal equinox. It helps if you try it on a rough surface or choose an egg with a bumpy end for better balance.
The myth comes from an assumption that during the equinox a special gravitational balance exists. The equinox is about balanced light, not balanced eggs or special gravity.
As an aside, a solstice occurs when the poles of the earth are tilted at their maximum away or toward the sun. At winter solstice, the pole is tilted furthest from the sun, at summer solstice it is tilted closest to the sun.