# Questions tagged [collision]

Interaction between two or more bodies that results in physical contact and an exchange of momentum between the bodies involved.

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### Elastic collision and spring

Bodies $A$ and $B$ are moving in the same direction in a straight line with a constant velocities on a frictionless surface. The mass and the velocity of $A$ are $2 \text{kg}$ and $10 \text{m/s}$. The ...
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### When a ball bounces on a wall at an angle, why does the angle of incidence equal angle of reflection?

When a ball is thrown to a wall without spin and bounces, supposing it's an elastic collision, why does the angle of incidence equal the angle "reflection" (relatively to the normal), why isn't it any ...
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### How does the central peak in moon craters form?

The central peak in many of the moon's large craters are visible with a telescope and they seem a little odd to me. Can someone explain how they form.
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### Mars just collided with Earth! A question of eccentricity

One of the standard theories behind the formation of our Moon is the giant impact hypothesis, according to which Earth was struck by a Mars-sized body (about $10\%$ the mass of Earth) early in its ...
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### What determines whether a pool ball will bouce backwards after colliding with another pool ball?

I'm no knowledgeable pool player, but I've noticed that sometimes when the cue ball hits another pool ball, they roll together; and sometimes the cue ball bounces back. And I have a very, very rough ...
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### Collision and simultaneity in special relativity

An almost rigid rectangle with length $D$ can rotate around its center. Assume that rectangle is horizontal and does not rotate before collision. According to observer $S$ two balls collide at the ...
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### Does Quantum Theory allow an Electron to take a fraction of Photon energy

In Photoelectric Effect of Theory of Spectral Lines , an electron takes the entire or none of the energy of the Photon ( it absorbs the entire quanta not its fractionS resulting in the disappearance ...
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### How do I describe and calculate the effect of an impacting object?

My lab studies the physiology of impact injury on biological tissues. I use a pneumatic cylinder to impart injury into a biological sample and then assess the molecular and physiological changes in ...
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### Explicit Function for Bouncing Ball [closed]

I was wondering if it's possible (and if so, how would you go about it) to write an explicit function for the position of a ball bouncing as a function of time (assuming a coefficient of restitution 0 ...
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### What is the best way to calculate impact time with collisions?

I've been teaching myself physics and I've been wondering about the impact time in collision calculations. The scenario I've been using to learn is an object with a mass of 4000 kilograms colliding ...
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### Factors on which Coefficient of restitution depend

What are the factors on which coefficient of restitution depend? What is the reason for more coefficient of restitution of two glass balls (0.95) than for two lead balls (0.20)?
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### Conservation of 4-momentum in special relativity

I understand that the inner product of two 4-vectors is conserved under the Lorentz transformations, so that the absolute value of the four momentum is the same in any reference frame. This is what I (...
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### Why does a continuous water stream form ripples when colliding with a surface? [duplicate]

I was in the shower one day washing my hair, and noticed that the water falling off my hair formed perfect streams that ceased to break into droplets for quiet some distance (probably about 5-6 cm). ...
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### Is the center of mass in general relativity equal to the center of mass in newtonian gravity?

Consider 2 point masses $A,B$ a distance $d$ away from each other without velocity or rotation spin. Is the center of mass in general relativity equal to the center of mass in newtonian gravity? In ...
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### How to tell if the collision is elastic or inelastic?

I'm a programmer and a game developer, not a mathematician or a physicist. So please go easy on the math :) I know two things: How to find the new velocities of two objects after an elastic ...
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### How do we know the actual position of the Andromeda galaxy, if we are seeing 2.5 million years in the past?

Scientists estimate that Andromeda and The Milky Way are going to collide in about 2.5 million years, how accurate is that calculation?
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### Small car colliding with large truck

A small car collides with a large truck. Why do both vehicles experience the same magnitude of force? Wouldn't the large vehicle experience less force than the small one?
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### What is the function of the top point of a bouncing ball?

A ball is thrown away as parallel to x axis from M(0,h) point with speed V . After each jumping on x axis , it can reach half of previous height as shown in the figure.(Assume that no any air ...
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### What is the maximal particle mass one can create via the LHC? Can we create dark-matter particles via the LHC?

Thanks to the LHC one can make particles collide and annihilate into other particles. Therefore, currently, what is the mass of the most massive particle one could create theoretically given the ...
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### What causes destruction in car crash?

Suppose a car crashes at a speed $v$ against a wall and comes to a stop. Now if the car crashes at $2v$, does that mean it suffers twice as much destruction, if that can be objectively measured? If ...
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### Is change in kinetic energy invariant?

Consider the inelastic collision between two bodies. This question follows on from this: Is the coefficient of restitution frame independent and energy conservation?. One of the answers to this ...
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### Special relativity and particle creation

Does special relativity predict the possibility of particle creation? Is it due to the relativistic energy-momentum dispersion $$E^{2}=m^{2}c^{4}+p^{2}c^{2}$$ which shows that mass is simply a form of ...
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### Is momentum conserved in the collision of a ball with a hanging rod?

Suppose we have a situation like A ball of some mass $m$ with some velocity collides with rod hinged at point $A$. Is momentum conserved in this situation? I know that hinge will give impulsive ...
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### Two questions about the coefficient of restitution

If you were to drop a ball onto a surface from a height $h$ and the ball collided with the surface and then rebounded, would the ball then travel a distance of $eh$ back up from the surface where $e$ ...
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### Help with equations for deflecting an asteroid

This is a homework assignment, but not the physics part. I have to write a python script to simulate the size of a warhead required to deflect an asteroid (parameters inputted by user) that is on a ...
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### Two objects exert forces on each other, will the reactions affect them?

Two objects go in against each other, and then they collide, will object 1, exerting force 1, necessarily get on it a reaction equal in magnitude and opposite in direction? EDIT:- In my book it only ...
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### Mathematical proof that the centre of mass energy is the smallest energy in a collision

I recently answered this question about how the energy of a system of colliding particles is minimised in the centre of mass frame. I'm happy with the qualitative answer that treating the collection ...
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### How an asteroid enters the Earth make a completely different outcome? [closed]

In this scenario there are different ways an asteroid could enter the Earth's crust but does the aftermath differ? Think of the surface of the Earth as thin sheet of ice and the magma the water ...
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### Why doesn't the 9th ball move in the break in the nine-ball pool game?

In the game of nine-ball pool, we break the rack like shown below: In the break, we hit the 1st ball with the cue ball. Many people familiar with pool games say that if the rack is constructed ...
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### Why does a particle-antiparticle collision produce $2$ photons instead of $1$?

In one of the questions that I did, it asked: What is produced when an electron and positron collides with each other? The answer is $2$ photons. Why doesn't it merge into one? After all, the photon ...