1. The problem statement, all variables and given/known data Note: To make this easier, gravity, air resistance, and friction do not exist in this problem. Given two boxes which are sitting directly next to eachother, and a force applied to the leftmost box in the rightward direction (straight at the other box), are there any rules/formulas for the amount of force which the leftmost box applies to the box it is sitting next to? Example: What causes the 1N force being applied to A to be smaller when A applies it to B? 2. Relevant equations 3. The attempt at a solution I have a vague theory that it has something to do with A "absorbing" some of the force due to its mass, but I haven't been able to get any further with this. As you can see, I can actually calculate what these values are, but the problem is that I don't understand why they are the way they are. It seems to me that if a 1N force is being applied in a rightward direction on A, then A would apply a 1N rightward force on the block to its right, which is B. However, this doesn't seem to be the case, at least not when viewed like this. I tried attacking this with the assumption that a 1N force is actually being applied to B, but is being partially counteracted somewhere. I didn't get very far with this approach either. I think I simply need someone to explain how this works, step by step.