All thrown weapons have kinetic energy based damage. When weapon is thrown energy of the throw is recalculated into throwing speed based on the weight of the thrown weapon. Initial throwing weapon is capped at 25 m / s since this speed seems to be limit of human hand based on the data from modern olympic throw but other modern disciplines as well. calculated speed is then artificially increased by 10 m / s and reduced on impact in the calculation by 10 m / s. This increase in speed is done to help AI throw at larger distance without artificially increasing their damage.

Energy of throw is calculated like this: 60 + skill * 0.8. This means that with 0 skill your throw has potential energy of 60 joules, at 100 skill its 140 joules and at 200 skill its 220 joules (which is comparable to olympic throwers when you remoce their run up speed in calculation of their KE). As mentioned earlier throwing speed is limited to 25 m / s, so you cannot reach 200 joules with light throwing dart however you can do that with heavy javelin. Speed of enemy, your run up speed or speed of your horse is also properly added to the speed of your projectile and the damage calculation. So leveling up throwing will improve your throwing speed and improve your ability to throw heavy javelins. Throwing from fast horse or at fast rider will significantly increase power of your thrown weapon.

Throwing axes will deal their kinetic energy + their weapon thrown damage as actual damage.
Javelins (and throwing spears) will deal their kinetic energy + their weapon thrown damage (mostly in 20-40 range).
Throwing daggers and throwing knives will deal their kinetic energy * 0.6 (because they are meme weapons that have no place on battlefield with any kind of armor). Thought they have still some use in civilian fights.