As you learned in a previous post, I have a background in physics. And you might have also noticed that I’ve included a lot of science in my fantasy stories. In fact, if you’ve finished Rising on Song, you will know what that post image is all about 😉.

But does the science fly? If you’re a science geek and want to know, I am doing a deeper dive into some of the hidden science behind my fantasy once in a while. Here’s my first shot.

Ballista

The ballista is an ancient missile weapon that launched stones and projectiles, usually at castle walls or gates. Although earlier models existed, the Romans adopted the one developed by Alexander the Great using torsion springs. The ballista I introduced in Adamant in Dust is a variant of this model.

The ballista looks and acts like a giant crossbow. In the torsion-powered ballista, the torsion springs are bundles of strong, tightly strung rope coils made of animal sinew. The bow arms of the ballista are inserted into two vertical springs attached to a frame. When the bowstring is winched back into firing position, the already tight torsion springs coil, storing potential energy. A bolt or stone is loaded onto the bowstring in a slide. When the bowstring is released, the springs snap back, and the energy hurls the projectile at a target.

The torque, or twisting force, that shoots the projectile depends on the torsion coefficient of the spring, among other things. And this torsion coefficient depends on the shear modulus of the rope material, the bundle’s length, diameter, and number of strands. About the shear modulus, suffice it to say that the larger it is for a material, the more potential energy it can store and the greater the force firing the missile.

In my story, Irvon, our resident genius, has replaced animal sinew with steel for the torsion springs. Steel has a shear modulus of approximately 80 times that of sinew. With steel coils, the springs can be smaller, and the ballista can be lighter and more portable, especially if steel also replaces wood for the body of the ballista.

In actuality, we need carefully constructed, high-quality steel to handle higher stresses, prevent material fatigue, and optimize efficiency. It is unlikely that anyone would have the necessary resources and know-how in medieval times to produce that kind of steel. But we are in a fantasy world, and Irvon is an extremely resourceful intellectual. I invite you to suspend your disbelief.

You can ask AI if you want to know more details and equations, or follow these links:

Wikipedia: ballista; The Real History of the Ballista, Game of Thrones’ Anti-Dragon Weapon

Colored Flames

Wanting to produce colored flames as flares in Adamant in Dust, I discovered which chemicals produced the different colors. Here is a list, but be careful if you wish to experiment yourself. And make sure you don’t substitute chlorates, nitrates, or permanganates because they produce harmful byproducts when burned.

• Blue flames – use copper chloride
• Turquoise flames – use copper sulfate (combination of sulfur & copper; found in plants, soil, food, water; blue crystal also called blue vitriol, bluestone)
• Red flames – use strontium chloride (salt of strontium and chloride; in minerals celestite & strontianite; celestite found in sedimentary rocks often associated with gypsum, anhydrite & halite)
• Pink flames – use lithium chloride
• Light green flames – use borax (evaporite of seasonal lakes, salt deposits)
• Green flames – use alum (mineral evaporite, salt deposits; found in Chad, Egypt, Morocco) or copper sulfate
• Orange flames – use sodium borate or calcium chloride
• Purple flames – use potassium chloride
• Yellow flames – use sodium chloride (table salt) or sodium carbonate
• White flames – use magnesium sulfate (Epsom salts)

Here are some links with more information, including how to produce colorful flames safely:

Creating Flame Colors; Colorful Campfires

Hot Air Balloon

Flight is an important element in the Far Stone Cycle. There are flying creatures and the machines that seek to emulate them. So, let’s explore the mechanics of one way to rise into the heavens: the hot air balloon.

Hot air balloons operate on the principle that warmer air rises in cooler air. Hot air is lighter because it has less mass per volume. A cubic foot of air at 100° F is 7 grams lighter than a cubic foot of air at room temperature. That’s not a lot, thus the need for hot air balloons to be enormous. It takes 65,000 cubic feet of hot air to lift 70 stones.

A hot air balloon consists of three essential parts: a burner to heat the air, a balloon envelope to hold the hot air, and a basket for passengers. The burner sits under an opening at the bottom of the balloon envelope. The balloon envelope material should be lightweight, sturdy, and heat-resistant with a high melting point, especially the skirt around the opening, closest to the burner.

Modern hot air balloons use nylon gores for the envelope, and propane gas fuels the burner. There are also cords to open valves at the top of the envelope, allowing hot air to escape and the balloon to slow its ascent or descend.

In our story, our intrepid inventor does not have these advance materials. But it might be all right since the balloon will only assist with lift and not be the sole agent to keep the flying vessel going.

Before we go on to explain more about flight, here are some links if you want to know more about hot air balloons:

How Do Hot Air Balloons Work; How do hot-air balloons work? – Explain that Stuff

Airplane Flight

You may think that it is an engine that causes a plane to fly. In fact, the engine simply moves the plane forward at high speed, forcing air to split above and below the wings, then downward, exiting the wings. It is this deflected, downward flow of air above and below the wings that generates lift, which raises the plane and keeps it in the air. It comes down to pressure differential and Newton’s Third Law of action and reaction.

The curving flow of air creates lower pressure above the wings and higher pressure below the wings, resulting in the upward lift. Tilting the wing slightly upward (the angle of attack) increases the area of lower pressure above. The higher pressure of the normal atmospheric air above the low-pressure area accelerates the air downward. Based on Newton’s Third Law, an upward force will counteract the downward flow, lifting the plane.

The angle of attack also creates a downward flow of air under the wings as the higher-pressure air right below the wings push down on the lower atmospheric air.

Why is the pressure above the wings lower and the pressure below the wings higher? Good question, and I’m not sure I understand it entirely. I believe it has something to do with the air stretching out above and compressed below because of the space created by the angle of attack.

Because they are much smarter than me, the inventors in Rising on Song know all the physics involved even if they cannot articulate it. But they don’t have a powerful engine to move the air fast enough to generate the necessary lift, so they added the hot air balloon. I’m not sure their contraption will fly in the real world. Fortunately, they don’t live there. But would it fly in their world? And what is it for? Find out in Book 3, coming out in 2026.

If you want to know more, here is a good website on the science of how airplanes work:

Airplanes