Why do hot molecules move faster than cold molecules?
481035
its the other way round. a thing is hot if its molecules are moving with a higher thermal velocity (prop to T^1/2). if you heat something its molecular vibrations go up in turn increasing its temperature.
1004425
The heavier the molecule, the slower it moves. The lighter the molecule the faster it moves.
779094
Molecules vibrate. As they vibrate faster, matter expands. The vibration is this energy we call heat. When vibration is lowered to a certain levels, matter becomes solid (water freezes), at the other end of the spectrum, when molecules agitate at a certain speed, liquids turn into gas (water evaporates).
605145
no...it cant get colder than absolute zero....thats why its called absolute....molecules dont move forward or backward ....you should think of them as energy particles....electrons dont really move around a nucleus either....dont think of them as planets around the sun they are more like energy fields.  the more negative the charge the more "electrons"....if there is any movement....even if it were possible to move backwards it would be warmer....movement causes friction and, therefore, heat.  it you cant get less than nothing.
756709
movement of molecules is primarily the only similarity. With active transport molecules move from an area of lesser concentration to an area of greater concentration, this requires energy.  Diffusion is also the movement of molecules but they move from an area of grater concentration to an area of lesser concentration; occurs because molecules have free energy, like the diffusion of o2 &co2 in the lungs
427727
Material objects (solid, liquid or gas) are made up of particles called molecules.   (Molecules are in turn made up of atoms, with one or more atoms per molecule).  These molecules are in constant motion, vibrating, rotating and translating (moving in a straight line).  Temperature is the mean kinetic energy (energy of motion) of the molecules making up an object.  Molecules don't all have the same kinetic energy, it's distributed randomly among them.\n\nWhen molecules collide (as they do constantly) they transfer kinetic energy.  When two systems of molecules come into contact, the molecules of the two systems collide and exchange kinetic energy.  The mean kinetic energies of the two systems even out: if one is colder than the other (lower mean kinetic energy) it becomes warmer (higher mean kinetic energy); if one is warmer it becomes colder.  \n\nWhen a clinical thermometer (or any thermometer) comes into contact with a warm object (a patient) the kinetic energy of the molecules of the thermometer warm up to match those of the warm object (since the patient is quite large & generates its own heat, the decrease in the patient's temperature is very small).  The thermometer typically has some liquid subsance (mercury, alcohol, ...) that expands when it warms, as molecules moving faster take up more space (bounce into each other harder, push each other further away).  So the "reading" of the thermometer goes up as the liquid within the thermometer expands.
434026
If you place a glass of hot water in an ice box it will actually freeze faster than a glass of cold water. \n The reason is that the temperature difference makes the water circulate in the warm glass transfering the heat loss evenly through the contents, in cold water the outside freezes first which insulates the inside from heat transfer keeping the center liquid.\n Try it, you'll see.
379311
sundevil is right, it has to do with the ability of matter to conduct heat away from your body. Since your body is always generating heat by cellular respiration (your cells burning food in order to function), your body will increase in temperature if there is nothing to take away the energy, causing you to feel hot. Gases are poor conductors of heat, so they have to be much cooler than you to be effective coolants. Once you transfer some heat to the air near you, that air has to transfer heat to other air near it before it can absorb any more. Gas molecules are far apart and  transfer energy betwen each other much less than solids and liquids. Your body will keep making itself hot faster than the air can cool it down. Liquids and solids have much larger heat capacities, so they can absorb energy without much raising in temperature and are much better conductors of heat, transfering energy to other molecules so they can absorb more.
285976
atoms are moving faster in hot water, and are hitting surface of the pill more often thus knocking molecules away from the pill more often, thus disolving faster
155067
The liquid molecules begin to heat up which causes them to increase their moleculer movement. They eventually move very far apart which causes them to be in the "gas" state.
180504
Heat is actually a microscale form of kinetic energy. The molecules of a hot object are in rapid motion; the hotter, the higher the average speed. If the object is gaseous the motion consists of free-path travel and collisions with other molecules. If it is liquid the paths between collisions are shorter, and if solid the motion is vibrational with no secular movement. \nIn conduction, heat is transferred by collisions between molecule populations with different average speeds. The transfer continues until both populations have the same average speed. \nIn convection, heat is transferred by mixing fluids of differing temperature. The mixing can be forced or driven by density differences caused by temperature difference. It is not necessary that molecular collisions occur in convection, since mixing alone changes the average molecular speeds.\nIn radiation, the molecular motion is converted to microwave or infrared energy by rigid motion of molecules or flexing of molecular bonds (ref.). Shorter wavelengths (light, UV, X-rays, gamma rays) are produced at higher temperatures where atomic electrons and nuclei may become involved. Radiative energy is not considered heat, but is converted to heat by absorption.
978480
Yes, in some specific circumstances, hotter water freezes faster than colder water.  All explanations are still hypotheses and there is no fully proven explanation yet for why.  It's known as the Mpemba effect.
908583
No, it does not.  However, the arrangement of the molecules does.  When the temperature is high, the molecules become very energetic and take the form of a gas as they move rapidly around and bounce off each other.  When the temperature drops sufficiently, the molecules take on a lattice structure because they are moving too slowly to resist intermolecular forces.
718611
The soda has more heat than the ice.  Heat energy travels from areas of greater heat to lesser heat.  The heat energy in the soda leaves the soda to go to the ice which in turn melts the ice, and leaves behind a cooler soda.\n\nHeat moves....cold doesn't.
96040
The phrasing is wierd, shouldn't there be a from between flow and the?\n\nIf two substances have different _temperatures_, heat will flow [from] the hotter [substance] to the colder [substance].\n\nThis is because heat, at the molecular level, is related to how fast molecules are moving. When a substance whose molecules are moving faster comes in contact with an object that's moving slower, the faster molecules will collide with the slower molecules of the second object, slowing down the faster molecules while speeding up the slower ones. Thus, heat (average kinetic energy of a substance) is transferred from the hotter substance to the colder one.
731331
I've heard that its the boiling water that freezes first. \n\nI think because the water molecules are hot (i.e. they are moving fast) the energy (or heat) will escape (move to equilibrium with other items in the freezer) at a faster rate than the water molecules in colder cup of water. \n\nBut really I'm mostly guessing with my explanation.
561115
Question -   Please explain how molecules in the air cause air\nresistance. Why air resistance is larger when a car a travelling faster?\n---------------------\nSharazaad,\n\nEven though you cannot see them, air molecules (a mixture of gases, mainly nitrogen and oxygen) are \njust like all other molecules inasmuch as they have mass and occupy space. Anything moving through \nair must push the molecules out of the way.\n\nThe faster the object moves, the faster the air molecules are encountered and the greater are the \nnumber to be pushed aside. This requires a larger force that necessary when the object is moving \nslowly. Consider swimming: The faster you swim, the harder it is to push the water molecules out \nof the way.\n\nStreamlining a car is a way of making it slip through the air more easily. Cars with narrow or \nwedge-shaped front ends and smooth, gentle curves allow it to slip through the air more easily \nthan bulky things like large trucks with large, boxy, flat front ends. Even something so simple \nas keeping a car clean and polished will help it slip through the air more easily.\n\nRegards,\nProfHoff 869\n=====================================================\nSharazaad,\n\n\nMolecules in the air have mass.  Even though they are invisible, they are\nstill there, and they still have to be pushed out of the way for a car to\noccupy the space that the air is in.  This now should make sense WHY air\nresistance even exists.\n\nNOW.  Why do greater speeds cause there to be an even greater air\nresistance.  It is true that there is barely any appreciable air resistance\nto a car going 10 MPH versus 60 MPH.  But at 60 MPH, even though there is\nthe same amount of air, the resistance is much greater because the car needs\nto move the air out of the way MUCH MUCH QUICKER.  I do not know if you can\nreally speak about viscosity of air (non - liquid).  But air really does\nbehave like a liquid when it comes to resistance.  HOW?  The air that is\nexisting on or above the sidewalk WILL ALSO RESIST the air molecule that is\nbeing struck by your car and pushed to the side.  SO, this is why at higher\nspeeds you will have a much greater resistance because you are FORCING THE\nAIR to move not at 10 MPH but NEEDING IT to move out of the way at 60 MPH.\n\nYou could say that the relationship between air resistance (r) and velocity\n(v) is proportional.  However, I think I read somewhere that resistance (r)\nis ~ velocity (v)^1.5\n\nPlease do not quote me on that ... but I am pretty certain I read it in an\nMath book for Engineers.  So there may be some credence to it.\n\nHope this helps.\nDarin Wagner\n=====================================================\nAir resistance is caused by the car banging into air molecules and\nincreasing their momentum in the direction the car is going.  Since the car\nexerts a forward directed force on the molecule, by Newton's 2nd law (for\nevery action there is an equal and opposite reaction) the molecule exerts a\nforce on the car in the backward direction, tending to slow the car.\n\n\nOf course, a molecule has so little mass, it exerts an extremely tiny force\non the car.  However, there are so many molecules that the cumulative effect\ncan be large.  You might also imagine what would happen if molecules were as\nlarge as bowling balls!  I think you can picture how the forces could be\nvery large.\n\n\nIncidentally, the molecules are moving at speeds much faster than the car is\ngoing and in random directions.  So some hit the car from the rear and speed\nit up a little (very little).  However, one coming from the front slows the\ncar down by a larger amount because the car's speed is added to the\nmolecule's speed for a molecule coming from the front and subtracted from\nthe molecule's speed for one coming from the rear.\n\n\nBest, Dick Plano, Professor of Physics emeritus, Rutgers University\n=====================================================\nHi Sharazaad,\n\nGood question,