Ok, this is about ancient warfare and tactics and how some of the physics behind them actually worked. So I have loved ancient warfare for the majority of my life. Over the years I've gained more and more knowledge about this subject, but a couple of questions seem to keep me wondering. The first two kind of have something to do with each other, but they both are some what independent.
In formations such as a phalanx or a shield wall you end up with an ungodly amount of force being exerted on the very front lines of the two forces colliding. With both sides pushing against each other, wouldnt the men in the front lines be literally squished and splattered simply from feeling the push of two armies on their fronts and backs? (like a giant sandwich).
My second question has a bit to do with the front line of a force being hit by the rest of its unit, but this question is about cavalry. In a cavalry charge with the horses galloping towards their target they hit with deadly force and come to a stop quite quickly, wouldnt this stop cause a load of friendly fire? I mean just think about it, you have a bunch of lancers moving forward at 30 or so mph and the front line of lancers comes to a halt.....wouldnt the rest simply not have time to slow and end up spearing their allies?
My last question is about when lancers hit their targets. If a lancer hits a lightly armored target dead center in the chest, wouldnt the lane get stuck in the target?
Also thanks to anyone that takes the time to read or comment. also i thought i should add a video in reference to the sandwich thing. you can clearly see that both sides are pushing on their front lines with the force of ever rank. https://youtu.be/HdNn5TZu6R8?t=1m37s
Our understanding of phalanx, and by extension, medieval pike warfare is very poor. There are contemporary references to it, but little detail about exactly what it looked like in action. Some people therefore have interpreted the sources as you describe, with it being basically a big rugby scrum, and the weight of the combined ranks being used to force the enemy back. This is the sort of thing usually seen in video enactments. Some people have pointed out the problems with this, as you describe, and because of these issues, have theorised a different interpretation, that the first ranks engaged, and the ranks following them were just there for replacements when front ranks fell, or for morale support, to literally 'back them up' since the more ranks you have behind you the less likely the fighters at the front are to run away. This is why the front ranks were usually the ones who were veterans and heavily armoured, while the back ranks were less armoured, less experienced, and paid less. It is impossible to know how they fought for sure, but personally I think the second theory to be the more reasonable interpretion of the evidence, and makes most sense when thinking about it in action.
Secondly, in a cavalry charge, the cavalry don't come to a sudden stop. The intent is for the unit being charged to break and disperse before the cavalry hit them. Then the cavalry pour through the dispersed infantry, hacking to the left and right with their sidearms. A cavalry charge is psychologically terrifying, and most infantry will break and run when a thousand armoured horsemen break into a gallop a few metres away from them with the very earth shaking under their hooves. Even if they know their best defence is to stand their ground, psychology works against them and they'll break and run.
The leader of a cavalry charge will have to judge the effect the charge is having on the enemy before they strike however, and if the infantry doesn't look like its going to break then they would call out an order to their unit and the cavalry will peel away to the side instead of hitting the infantry head on. This is because, as you say charging into a wall of infantry standing their ground is suicide, and no horse will do it, let alone their riders. Horses aren't stupid and if you try riding one straight into a wall of lances, you're going to have a bad time. They'll baulk, throw their riders, etc, and the charge will turn into a chaotic mass of horses crashing into themselves and sharp objects.
And finally, lances were designed to shatter if they hit a target head on. Cavalry would use their lance once for a single devestating blow, and then switch to a sidearm for close quarter melee fighting such as a mace or halberd against armoured opponents, or axe or sword against unarmoured opponents.