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Stars are powered by nuclear fusion
Before reading this section, you will first need to know
Atoms are the smallest stable building blocks of matter in the universe
Atoms are not solid. They are made of protons, neutrons, and electrons.
All solids, liquids, gases and plasma in our universe are made of these particles.
All matter is attracted to other matter through gravity. If you have enough mass floating around in space, over time, large amounts of matter will be attracted together to form giant gas clouds – nebulas.
Nebulas themselves can contract, due to gravity. This leads to the development of stars
Generally speaking, all matter in our universe is conserved (conservation of matter)
Generally speaking, all energy in our universe is conserved (conservation of energy)
Here’s the wacky bit: scientists discovered fascinating and unexpected violations of those supposedly inviolable laws, but instead of that being magic, it pointed towards an even greater discovery: the law of conservation of matter and energy. This was discovered by Albert Einstein, and is known as mass–energy equivalence.
As such, first read our lesson on the discovery of nuclear physics and radioactivity.
At this point you now have the background for what comes next.
Inside a star, gravity pulls billions of tons of matter towards the center. Atoms are pushed very close together. So close that sometimes two atoms will fuse into one, heavier atom. The mass of this new atom is slightly less than the mass of the pieces that it was made of in the first place? Where the did missing go? It effectively becomes energy – which we see as photons, or as the heat/motion energy of other particles.
As an example, here we see deuterium fusing with tritium. The resulting product has less mass than the parts going in to the collision. That missing mass we see becomes 3.5 mega electron-volts of energy,
Here we some typical nuclear fusion reactions that go on inside yellow dwarf stars like our sun.
Here is a step-by-step cascade showing how hydrogen atoms can fuse to create Helium, giving off gamma rays and neutrinos in the process.
(More text TBA)
A catapult is any one of a number of non-handheld mechanical devices used to throw a projectile a great distance without the aid of an explosive substance—particularly various types of ancient and medieval siege engines.
The name is the Latinized form of the Ancient Greek καταπέλτης – katapeltes, from κατά – kata (downwards, into, against) and πάλλω – pallo (to poise or sway a missile before it is thrown.) [from Wikipedia]
Ideas on how to build them at home
Today’s Latin lesson:
“Cum catapultae proscriptae erunt tum soli proscripti catapultas habebunt.”
( “When catapults are outlawed, only outlaws will have catapults.” )
“Catapultam habeo. Nisi pecuniam omnem mihi dabis, ad caput tuum saxum immane mittam”
( “I have a catapult. Give me all your money, or I will fling an enormous rock at your head.” )
If you lived in the Dark Ages, and you were a catapult operator, I bet the most common question people would ask is, ‘Can’t you make it shoot farther?’ No. I’m sorry. That’s as far as it shoots.”
– Jack Handy, Deep Thoughts, Saturday Night Live
Build an onager, ballista or trebuchet.
Grading rubric. The project is worth 100 points.
Timeliness: Late projects lose 5 points per day.
A. Catapults use torsion (energy stored in a twisted rope or other material.) Do not merely use a stretched elastic (e.g. rubber band.)
If you build a trebuchet then you will need to use a pivoting beam and a counterweight.
B. It will have some kind of trigger or switch. (Without such a trigger, you would merely have a large slingshot.)
C. The payload range will be nearly constant (each payload lands within 15% of the other payloads.)
D. It will have adjustable firing: One setting will yield a shorter range (at least 4 feet.), while another setting yields a longer range (at least 8 feet.)
E. The weight limit is 10 pounds.
F. The longest allowable dimensions of height, length and width are 50 centimeters for each.
100 points Machine built according to the above characteristics
– 20 points Minimum range is not met.
– 20 points Too large or too heavy.
– 10 points Firing range is not adjustable.
– 10 points Uses a stretched elastic material (e.g. rubber band) as the only source of power. (Not applicable for trebuchets, of course.)
– 10 points No trigger.
– 5 points Payload range is not constant