# Chris

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 Dec8 comment Please describe how a vacuum flask/thermos works Yes, it stops the heat transfer through "conduction" predominantly, as the vacuum has no particles in it to vibrate and transfer the energy from inside the insulator to the outside. Heat can still be lost through radiation however, because radiation can travel through a vacuum, as evidenced by the sun rays reaching earth. Nov29 comment how can galaxies collide if everything moving outwards @jmarkmurphy, it does make sense. Because I said they are getting further apart in general, but there are exceptions. Think of ants on an expanding baloon. If each ant is stationary, each ant appears to be moving away from each other ant as the baloon expands. But immagine if you have a rogue ant that walks along the balloon, it is possible for this ant to collide with the other ants, despite the expansion of the ants universe (ie the baloon). The expansion of space is more than simply galaxies moving away from each other, but rather the space fabric expanding. Nov28 comment how can galaxies collide if everything moving outwards No they are not getting closer they are getting further apart in general as outlined by hubbles law. This is due to universe expanding. This gives rise to red shift. However this does not mean galaxies could not collide just because the underlying space is expanding Nov25 awarded Revival Nov20 comment Constant Velocity 'Force'? Basic classical mechanics you should learn newton's laws, and Free Body Diagrams. To understand the forces acting upon a wall, an understanding of "free body diagrams" should enable you to do so, by labeling all the support structures applying forces to the wall itself. To master this, you must first master equillibrium and statics from classical mechanics, e.g. physicsclassroom.com/class/vectors/u3l3c.cfm Nov20 comment Constant Velocity 'Force'? @HaniSayegh, now it becomes complex, because it depends upon the arrangments of the atoms in the wall. Technically you only would take the atoms that are in contact with the ball. Then these atoms will contact atoms behind it, causing a new collision, and a chain reaction of collisions within the wall. It is complicated because the wall is held in place by support structures, so ultimately the force will be transferred from the wall to the support structres in the ground. Nov20 comment Constant Velocity 'Force'? Yes, except points (2) (3) and (4) occur simultaneously. That is, the electrons in the ball are pushing the wall back, while the electrons in the wall are pushing the ball back. Immagine I had just 2 electrons and fired them at each other, they will get to the middle and then both repel from each other simultaneously. You wouldn't say that one electron was the main culprit, both electrons affected each other. Nov20 comment Constant Velocity 'Force'? 1) Ball hits the wall. 2) Atoms in ball and wall oppose each other, which generates a force, causing the ball to reflect of the wall, and causing the wall to reflect off the ball. Nov20 comment Constant Velocity 'Force'? @HaniSayegh, the wall doesn't appear to accelerate backwards because the acceleration is small, because of increased mass of the wall and supporting structures which provide an opposing force on the wall to resist its acceleration. (F=ma, so large mass means less acceleration). Locally however just where the ball hits the wall, you can see the wall move inwards a little bit with a slow motion camera. Nov20 comment Constant Velocity 'Force'? @HaniSayegh, the wall accelerates backwards, and the ball accelerates forwards (Newton's 3rd law). The wall doesn't have to accelerate forwards to apply a force. Acceleration results from force, you don't need forward acceleration to produce a force. Nov20 accepted Schrödinger equation for two particles in a 3D box? Nov19 comment How is it possible to move something without completely lifting it? Nice answer. Do you end up using a greater magnitude of force overall when lifting and pushing, compared to just pushing? Nov19 asked Schrödinger equation for two particles in a 3D box? Nov18 revised Srednicki's book on QFT homework tag Nov18 suggested suggested edit on Srednicki's book on QFT Nov16 comment Constant Velocity 'Force'? Yes that is correct. Nov16 revised Bouncing Ball Pattern edited tags Nov15 accepted In a game of tug of war, what concepts are involved in determining where the rope breaks? Nov15 answered Constant Velocity 'Force'? Nov15 asked In a game of tug of war, what concepts are involved in determining where the rope breaks?