Inverse Kinematics is a term that’s derived from Robotics. It’s the concept of where segments can be calculated to produce a certain distance & angle to reach a goal. There’s a multitude of ways to accomplish this but, triangles seem to be the most common method. The best example I can think of on the top of my head would be your arm. Your shoulder is your starting position. Your shoulder to your elbow would be segmented as is the elbow to your hand. When you go to grab something, you’ll notice that your arm makes a certain angle and rotation to reach that object.
Here’s a better example of the concept: Inverse kinematics - Wikipedia
Here’s a neat Roblox example of the concept: 2 Joint 2 Limb Inverse Kinematics
Momentum is the mass and velocity of an object. Momentum - Wikipedia