J.C.MacSwell

That looks like a legitimate site (is it?), but the article sounds like something out of "The Onion".

Starting with the bold the answer is yes. If you can collide with the 100mph train where the collision lasts a few seconds, at constant force, you could survive it quite nicely. Good luck accomplishing this if you jump in front of it. For the above you can't calculate the force from initial conditions or even final conditions unless you know the time t of the collision. If you know that you can calculate the average force during that time, but you would still not know the peak force.

Seems somewhat like a lock in a canal using air instead of water, and somewhat like a human cannon. Making it strong enough to handle internal pressure would be relatively easy. Supporting a tower that high would be one amazing feat of engineering.

Why is velocity constant? If there is a collision they must have been on converging paths and therefore had different initial velocities. Unless they moved through each other, essentially missed or not collided, they would each have changed velocities.

Who is claiming that it is? All I have been doing is pointing out where the momentum went in the examples in answer to "How is momentum conserved?" What problem? They certainly take the momentum of the fluid into account when choosing and placing the brackets. Do you think I'm suggesting everything should be calculated for every application? Who solves any problem related to water flow around an elbow with Navier Stokes Equations? Flow around an elbow is virtually always turbulent. Navier Stokes Equations for this application would be unsolvable, or with enough simplifying assumptions unreliable, for any practical application where the answer wasn't already known. Understanding of basic principals are essential when making simplifying assumptions and choosing your equations. If sinks and sources are fully understood they may help explain how momentum is conserved. If not they might hide it. Tell me if the following is not misleading with regard to momentum : I think this describes where the energy goes quite well. All I was attempting to do was clarify what seemed unnecessarily complicated and somewhat ambiguous with regard to momentum.

Extremely reasonable...and that is why it can be confusing with regard to conservation of momentum, which is a fairly simple concept. Changes of reference frames, observer dependency, momentum sources or sinks, and external forces can be useful ideas or tools to simplify getting a solution for a particular situation, but IMO they cloud the issue when trying to understand conservation of momentum in the most basic way.

The point is with regard to the momentum. The change in the Earths momentum is the same and opposite of that of the ball. Momentum is conserved. Using an example where one mass is so large relative to the other can be misleading with regard to that point. The force on the Earth and the resulting change in it's momentum, due to the interaction with the ball, may seem insignificant - but it is exactly equal but opposite to the force and resulting change in momentum of the much smaller ball. You may understand that, but I think it should be kept clear to the OP.

True, but in each case if you look at the whole system, including the ball and the Earth, the forces are internal and in each case momentum is conserved at all times. Any momentum gained or lost by the ball is respectively lost or gained by the Earth.

What does that imply then, about the importance of life in general, if you only live one millionth of that time?

I hardly watch the show, but I'm pretty sure they are all siblings in real life.

You can certainly produce lift ( force perpendicular to the flow), at the expense of drag, with an underwater appendage. If positioned and oriented properly it will counteract heel. The problem is with positioning and orienting it so that it does not produce additional leeway or excessive drag, and at the same time act at sufficient distance from the center of buoyancy or center of gravity to produce the leverage required to counteract a reasonable amount of heel for the drag the additional structure will create. Other concerns would be the stability and control of the system and the minimization of it's affect at low speed. At say, half speed while accelerating it would produce only one quarter of the counteracting of the heel.

Don't you lose some immunities over time? I think this is a short term effect in the case of the mother/child.

For me, background temperature. Similarly, I think where it (the background temperature) is the same in all directions is a preferred reference frame, although maybe it is more of a continuum of frames. Edit: I picked this one in a long term sense. I would be pretty messed up if I was traveling at relativistic speed relative to my above preferred reference frame and used that description of simultaneity for my daily routine even if I could use it precisely. Similarly I generally use the Earth or perhaps the vehicle I'm in as my reference frame.

Any momentum gained by one is lost by the other. Both might be "slowed down", each may have lost speed in the direction they were headed, but when you add their momentums together, it will add up to the same total momentum (same total mass movement in the same direction)

Consider a completely inelastic collision between two objects. They collide and stick together. Total momentum (a vector quantity) is conserved, yet total kinetic energy (a scalar quantity) is lost no matter what inertial frame you use for measurement.

13 billion years later it still seems appropriate.

I think you have to be careful in assuming the error is related to the contact area of the tread. The gaps between treads are for the most part compensated for by "bridging", where there is an increased pressure locally where the tread contacts the road compared to the consistent pressure on the inside. I think the error is more likely related to the area near the perimeter of the contact area where the contact pressure would be reduced compared to the inside pressure due to the stiffness of the tire. This reduced pressure area would be insignificant on something such as a balloon, where the stresses on the skin are almost purely tensile.

If you use that definition (which is not correct), any straight line drawn anywhere (or it's extensions) would be tangent to the surface of the Sun, since it would have one point (the closest point to the Sun) that could have a line drawn perpendicular to it that aimed directly at the Sun and of course you could then add a circle somewhere as needed to meet that definition. Of course that is not the definition of tangent (see GDG's post above). Every straight line everywhere is parallel to some tangent line that contacts a point on the Sun's surface since that there could be one drawn in any direction.(actually there could be two drawn in any direction)

The rotational axis of Earth would be at right angles to a line between the Earth and Sun at those points, but not tangent to the surface of the Sun.

It will continue (wobble about) on the same axis of rotation as it had instantaneously on the moment of release. That axis is different from the one it was constrained to rotate about originally, and will depend on the original axis, and the moment of inertia about the bar axis relative to the moment of inertia about an axis perpendicular to the bar. Of course, kinetic energy and angular momentum will be conserved.

3) wobble

Homework, Ouch! That is what I'm here trying to avoid! (actually it's been quite a while since I was a student) I agree that your scenario is much simpler. In fact if Supermassive Black holes exist, and Black Holes are at all common, it would probably unlikely for the Supermassive BH's not to have smaller BH's meander into their event horizon now and then. I will try to remember your link and look it up when I get a chance.

Persistent little bugger!

Yes. She sounds like a very nice old lady. Maybe you could introduce her to the OP. She will know what to do.

http://www.amazon.com/Cosmic-Code-Quantum-Physics-Language/dp/0553246259