Quote Originally Posted by Bodeni View Post
Sorry I'm a BA not a BSc student. Force= Mass x Acceleration. Speed doesn't matter, after all we're all travelling thousands of kph around the sun at all times...
And I agree completely with Ibrahim's description, sorry I didn't explain the horse part fully.
??????

velocity* does actually matter in this situation (the cavalry charge): in fact it's pretty much the only reason there is a force imparted when the lance hits the target (think about it: the horse is pretty much at constant velocity just before impact, as is the the rider). This is because it imparts kinetic energy and momentum to the lance charge**. the kinetic energy is transferred into the target on impact (at least ideally), which is where force comes in (force in this case is kE/s***, where s is displacement--basically the distance the person theoretically recoils back from the blow.

This of course is ideal: we are not accounting for friction here, between the lance and the hand and/or armpit, and between the rider and the horse. nor are we accounting for the person flexing his back, or a host of other factors.


* srsly people: Speed=/= velocity in physics. velocity is a vector quantity.

**kE=0.5mv^2 (v is squared, so matters more than mass). p=mv (p is momentum).

***W=Fscos(theta), where W is work (measured in Joules, as is kinetic energy: they're basically two forms of the same thing), and since the impact is more or less head on, we can ifnore cos(theta), since the cos(0) is 1. so W=Fs, and so F=W/s. substituting W for kE (again, yes, this is fine), we get F=kE/s.