I will be using a lot of approximations to calculate these results. An exhaustive investigation is not really necessary in this case because we just want to develop a ‘feel’ for what the situation is going to be like. And of course, for those who cannot work out that I have my tongue firmly in my cheek for this article, we are talking about an event that can never actually happen. It is not within the bounds of human ability.

The speed of the return stroke in a lightning discharge is approximately a third of the speed of light. This is INSANELY fast! The speed of light in a vacuum is 299,792,458 m/s. This equates to about 1080 million km/h. So the return lightning stroke is travelling at approximately 360 million km/h. To put this speed into perspective, the circumference of the earth is 40, 075km. So in 1 millisecond, something travelling at the speed of lightning would have circled the earth. The speed of sound is approximately 330m/s, so at the speed of lightning, we are moving faster than Mach 30,000. As you can already no doubt imagine, my trendy Feiyues and silky black pyjama pants are probably going to ignite and disintegrate at those kinds of speeds leaving me somewhat exposed, but we’ll carry on and grind some more numbers out of this unlikely scenario.

If we simplify things and call the speed of light 300,000,000 m/s, the lightning will be travelling at 100,000,000 m/s. We will use this value in the rest of our calculations.

**Kinetic Energy
**

You should remember the formula for kinetic energy from high school science class:

**K.E. = 1/2 m v2**(Kinetic Energy equals half mass times velocity squared)

The mass that we will be working with for simplicity is the mass of my leg, which is 17.5% of my body mass or 14kg. Plugging this into the equation yields a maximum kinetic energy of 7 X 10^16 joules.

The yield of a nuclear weapon is a measure of the amount of explosive energy it can release. The yield is given in terms of a quantity of TNT which would generate the same amount of explosive energy. For each gram of TNT exploded, 4184 joules of energy are released. This means that when I kick at the speed of lightning, I will be releasing an equivalent amount of energy to a 16 Megaton nuclear weapon.

You wouldn’t want to be at ground zero for that kick. Neither would I, for that matter, and I’m supposed to be the one doing the kicking! When we are dealing with these kinds of energies and speeds, a lot of heat and explosive energy would be released. The kick would probably create a giant shock-wave very much like a nuclear weapon, shattering windows and setting fires in a radius of a few kilometres around. Apparently, a bomb with a yield of 1 megaton would destroy approximately 80 square miles of land (DeVolpi et al. 2004). My kick could possibly destroy a large percentage of the Darling Downs and Toowoomba area.

**Force
**

I thought it would also be interesting to calculate the amount of force required to accelerate the mass of my leg to the speed of lightning. We can also use the simple relationship which you would have learned at school:

F = ma (Force equals mass times acceleration)

Acceleration is easy to calculate because we will assume that my leg started at rest and ended at the speed of lightning. If we assume that my leg is travelling 750mm in the kick (0.75m), we can use the kinematic equations to calculate the acceleration.

I will use the equation:

**v² = v₀² + 2a(x-x₀) **(Final velocity squared (v²) is equal to the initial velocity squared (v₀²) plus twice the acceleration (2a) times the difference of distance and initial distance (x-x₀) or the change in difference.)

Rearranging and solving for acceleration yields an acceleration of 6.6X10^15 metres per second squared. Solving for force assuming that my leg weighs 14kg as before yields 9.3X10^16 newtons of force required to accelerate my leg to the speed of lightning over 0.75m.

To put this into perspective, the acceleration due to gravity on earth is approximately 10m/s which allows us to compute what this kind of force would be able to lift. Around 9X10^15 kilograms or 9X10^12 tons. This is an order of magnitude heavier than the mass of a typical mountain (3X10^14kg). I don’t think that the leg-press machine at the gym goes up to that kind of weight. Not that I follow comic books, but apparently the Hulk can lift the weight of a mountain. But can he do it with just one leg? It is possible that not even the Hulk can summon sufficient force in one leg to kick as fast as lightning.

And remember that the song doesn’t go “That kick was as fast as lightning.”, it goes, “*Those kicks*…” (plural), “were fast as lightning.” Oh, the humanity! What level of Armageddon are we talking about here? Perhaps this is what killed off all the dinosaurs.

Actually… A possible perpetrator is beginning to take shape through the haze of numbers and the settling dust of approximations. He strides forward and our blood freezes. It certainly isn’t me. There is only one man who could be responsible for kicks as fast as lightning. Chuck Norris. Wearing his Chuck Norris Action Jeans (TM.) with elasticated crotch area.

So all-in-all I would have to agree with the next line in the song. It would be a little bit frightening.

*Written by SiFu Lester Walters, head of the Chinese Martial Arts and Health Centre Australia
*

**Reference:**

DeVolpi, Alexander, Simonenko, Vadim, and Stanford, George. Nuclear Shadowboxing: Cold War Redux. 2 vols. Kalamazoo: Fidlar Doubleday, 2004.

**Cover image:
**“Karate kick at sunrise” by bluesbby, CC BY 2.0, available at: https://www.flickr.com/photos/17367470@N05/5398040497