Kinetic weapons have been around since the beginning.
Samuel 17
40 Then he took his staff in his hand, chose five smooth stones from the stream, put them in the pouch of his shepherds bag and, with his sling in his hand, approached the Philistine.
49 Reaching into his bag and taking out a stone, he slung it and struck the Philistine on the forehead. The stone sank into his forehead, and he fell facedown on the ground.
50 So David triumphed over the Philistine with a sling and a stone; without a sword in his hand he struck down the Philistine and killed him.
Its based on Newton's second law of motion which is stated as follows: The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force. Or F=M*A, Force = Mass times Acceleration, in laymans terms the faster it moves or the more it weighs the harder it hits you.
The principle has been used by the Chinese as early as the 4th Century and Europeans in middle ages.
It was Used By the French in WWI
By the US in Vietnam, With Lazy Dog Bombs
And Beehive anti personnel Artillery Rounds
More Recently By US in Iraq and the French In Libya
The newer projectile was successfully Tested at Holloman Air Force Base in New Mexico 2013
2004 Project Thor Concept
Current Projectile
Kinetic weapons have been around since the beginning...
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Lets not forget catapults and trebuchets.