Thanks all. Easy when getting it explained. Net linear momentum is the same so this means impulse have to be the same too.
Actually I was thinking about gas molecules in a container. If heating would increase weight. The ball example shows it can't increase pressure on the bottom. David David Jonsson, Sweden, phone callto:+46703000370 On Sun, Jan 23, 2011 at 3:36 AM, John Berry <[email protected]> wrote: > Of course, in practice the results can sometimes indicate that momentum > isn't conserved. > > This example is in principle not dissimilar to some inertial propulsion > concepts and there is evidence that some may work. > > > On Sun, Jan 23, 2011 at 3:19 PM, Stephen A. Lawrence <[email protected]>wrote: > >> >> >> On 01/22/2011 08:39 PM, David Jonsson wrote: >> > Hi >> > >> > Imagine a ball lying on a plane. The wheight is the mass times the >> > gravitational acceleration. >> > >> > Imagine a bouncing ball. Momentarilly the force from it on the plane >> > is higher and when it is in the air the force is zero. >> > >> > My question is if the time averaged force from the two different >> > situations are the same or if either ball has a higher time averaged >> > force on the plane below. >> >> Time averaged force is the same; otherwise momentum isn't conserved. >> >> Assume a cycle takes time 't'. >> >> Net change in the ball's momentum over one cycle is zero (since it ends >> up going at the same speed, in the same direction, as it was to start >> with). Therefore, total momentum added to the ball during one cycle, >> from all sources, must sum to zero. >> >> Total momentum from gravity is g*m*t. >> >> Total momentum from the bounce force is F*T, where F is the force of the >> bounce and T is the duration of the bounce. >> >> The two must be equal, so F*T = g*m*t. >> >> Average upward force is >> >> A = F * (T/t) >> >> so >> >> A = (F*T)/t = (g*m*t) / t = g*m >> >> ************************** >> >> And when a truck full of chickens with 3 ton gross weight is about to >> drive over a bridge rated at 2 tons, it doesn't do the driver any good >> at all to bang on the side of the truck. The chickens all fly up into >> the air inside the truck, but none the less, it still requires 3 tons of >> upward force on the wheels to support the truck and chickens. ('Course, >> if he's got a ton of chickens on board, chances are they're too fat to >> fly, anyway.) >> >> >> > >> > Good night ( 02:38 AM in Stockholm), >> > David >> > >> > David Jonsson, Sweden, phone callto:+46703000370 >> > >> >> >
