scilearner

Velocity I mean. Ignore the previous posts. This is the question I have. I was finally able to word it. Now let's say there was an object with initial momentum of 1 (m=1 v=1)and final momentum of -1(v=-1). That means change of momentum is -1-1= -2. Now if I consider the change in kinetic energy of the object 1-1 is zero. This is my biggest question, how come there is a change of momentum with out a change in energy.

Thanks swansoft Ok that makes sense. So in this situation does the ball lose or gain momentum. I understood your reason for why the wall doesn't move but this is my problem I don't understand how direction of movement after a collison is determined. EDIT: New question is below.

Hello everyone, Let's say there was gun and a bullet with a mass of 1kg at rest. The bullet and guns speeds were 2 m/s in opposite directions after firing if I right the equations. Kinetic energy 0.5m1v12 + 0.5m2v12 = 0.5m1v22 + 0.5m2v22 Why doesn't this equation work when objects are at rest. Mathematically I can understand but why physcially. Can anyone explain what is happening to kinetic energy in this scenario. Why does conservation of momentum equation hold in in inelastic collisions but not this one. I understand some energy is lost but why is it not affecting momentum.

Thanks for the reply Gains momentum from the wall? If the wall is stationarry before and after the collision. It's change in momentum is zero. So how does the ball get a change in momentum?

If I push a spring on a stationary wall and release, the spring would fly in the opposite direction right? I understand that there is elastic potential energy stored and this causes the movement but when I normally compress a spring it springs back to its orginal shape, how does it fly away in other direction. For example when I compress a spring against a wall, why doesn't it regain its original shape and fall down, why does it fly away instead. I'm thinking the elastic potential energy is used to make the spring go back to its orginal shape. Thanks I'm trying to understand newton's third law using this. If I push a book, it will push back on me. How does this occur using spring example. When I push the book does my hand compress a bit and then I move back in the other direction, ok but isn't the book compressed a little bit as well, wouldn't the make the book spring back and move back. How does the book move foward, if I compress it, shouldn't it spring back.

Ok you are right but what I was meaning to say was an object moves if it has kinetic energy. I mean if force is the rate at which a body gains momentum, that means force gives energy to an object. Once an object has kinetic energy it keeps moving, so force is not needed for movement, are you saying it is needed to start the process, but when it starts doesn't it do by transferring energy. Anyway may be you are right but I'm very confused at the moment. I have another question. Let's say a box was moving forward at constant speed, it must have some energy, then a force in opposite direction acts on it to make the object stop, how has the negative force removed energy from the object, has it been transferred to heat? Also if I keep applying this force, the object would eventually accelerate the opposite side, how come now the negative force is giving energy to object and before it was taking away. Thanks

Thanks swansoft Can you also help me with my last question. If their is a box at rest and two people are pushing it with equal force in opposite directions. The object stays at rest. My question is what happens to the energy provided by two people. Does it cancel (how?), or does the object keep gaining energy without moving? I don't understand how forces give energy in a certain direction, what determines the direction?

Hello everyone, I don't know I have got really confused. Now if an object has energy, it can move. Is their any scientific explanation in molecular level or something why does energy make an object move. Also how do net forces work. If their is a box at rest and two people are pushing it with equal force in opposite directions. The object stays at rest. My question is what happens to the energy provided by two people. Does it cancel (how?), or does the object keep gaining energy without moving? I don't understand how forces give energy in a certain direction, what determines the direction? Thanks!!

Thanks Physics fan I always like when equations start to make sense My question is however more on let's say I push a box on the floor, it gains energy and moves. Why does an object decide to change in position when energy is gained. Is this something we know because of observation. I think this question is more philosophical.

Thanks Physics fan I always like when equations start to make sense My question is however more on let's say I push a box on the floor, it gains energy and moves. Why does an object decide to change in position when energy is gained. Is this something we know because of observation. I think this question is more philosophical.

Hello everyone, May be the question is when something has energy and there is no resistance why does it move? Thanks

Hello everyone, May be the question is when something has energy and there is no resistance why does it move? Thanks

Thanks Grieppi. I appreciate your detailed response So even if there is no blood vessel cut, say from a physical wound, when inflammation occurs does everything occur. I mean if an infectious agent get it even if it doesn't attack blood vessel do platelets begin to aggregate and stuff. Also let's say they say a particular cell is infected. If it is a virus it would probably have gone inside the cell and then lyse destroying it. If the cell is infected by bacteria, what do they exactly mean. Do bacteria live inside cells, or are they saying bacteria outside the cell using the resources of the cell. My question is not related to artherscelrosis, although I know a bit about with formation of foam cells. Thanks again

Ok I see. Thanks

Hello everyone, I saw this in something I read recently. The infection could cause thrombosis. Ok my question is if thrombosis is a blood clot that occludes a vessel, how does infection create one. If the blood vessel is damaged some how it is possible. Are they saying bacteria or something from the infection can damage blood vessels, how by their toxins? or is this caused by swelling? Also how does a thrombosis occur. I mean in animations I have seen when a vessel is damaged, fibrin and all close the gap nicely, what makes them overdo their stuff. Also this is just another general question, in infections is it mostly the bodies immune response (swelling) that is damaging more than the infection? Thanks a lot

Thanks swansoft Anyway I want to clarify again. If an object is moving and someone asks me what is its internal energy. Is it thermal energy+other energies you decribed or thermal energy+other energies+kinetic energy of centre of mass. Kinetic energy of centre of mass is this always less than the thermal energy. Thanks

Thanks Skeptic. That last point I don't think I would have figured out myself EDIT: Wait that also answers one of my other questions I think. The difference between kinetic energy and heat. Is kinetic energy simply energy due to movement in one direction and heat just randon motion of molecules? If an object is moving at constant speed and I want to work out its total energy, do I add heat+kinetic energy or is heat simply its total energy. I think it is heat+kinetic energy. This is just to confirm.

Hello everyone, Ok the definition of heat says it is the total kinetic energy due to random motion of molecules. My question is it really the total kinetic energy. For example I know in inelastic collision heat is released. So is thermal energy really heat released in inelastic collison of molecules. Also if there is a bunch of molecules in a container and they all had elastic collisions, would there be heat in the container. Thanks !! Merged post follows: Consecutive posts merged Edit: Oh I think I worked it out. Tell me if it is right. The total kinetic energy of individual particles in an object is thermal energy (This is what gives temperature). In inelastic collision heat is given off (which is like like loss of thermal energy because heat is energy transfer). Heat is given off when molecules collide with surrounding air and give some energy I think, this is for an example. In elastic collisions, the shape comes back to orginal shape, so no energy is lost. Also this definition from another website helped me.

Thanks again After reading your reply and thinking I think I understood it. If there is a box in the back seat of the car, and the car is travelling straight and suddenly acted upon by the centripetal force, the box would obviously try to keep moving forward with cars orginal speed, but the centripetal force has already turned the car, so the box is not going to hit the front seat but the side of the car.

Thanks swansoft for the reply Ok then I haven't understood this concept. Ok a person was initially travelling at V direction and then centriptal force acted upon him to make him go in a circle. Now if centrifugal force is inertia, why is acting opposite to centripetal force, shouldn't it act tangent to the circle, if I stop the centripetal force the man would travel tangent to the circle. If inertia is in that direction why is centifugal force acting some other way, also I read that this force really doesn't exist, then how does it separate the liquid. Thanks!!

Thanks Double K

Hello everyone, If some test tubes are placed in a centrifuge to separate the liquid in them, does the separation occur after the spinning is finished. I can't see how the centrifugal force can act when the tubes are spinning, does it act after it finishes. Thanks

Hello everyone, This is the definition of endosteum from wiki, The endosteum (plural endostea) is a thin layer of connective tissue which lines the surface of the bony tissue that forms the medullary cavity of long bones. However I'm of the beleif that endosteum lines the inner surface of all bones. Does it only line medullary cavity or internal surfaces of all bones. Do all bones have medullary cavities by the way. Thanks

Hey thanks for the response . What do you mean a subconscious stimulus? Could you give me an example. Thanks

Hello everyone, For example muscle tone is continuous and passive partial contraction of the muscles. This means there must be some involuntary nerve impulses. Now my question is I can understand how heart has leaky potassium channels and contract involuntary, but how does the brain make nerves contract involuntary without stimulus? Thanks