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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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173
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3answers
65k views

Why doesn't matter pass through other matter if atoms are 99.999% empty space?

The ghostly passage of one body through another is obviously out of the question if the continuum assumption were valid, but we know that at the micro, nano, pico levels (and beyond) this is not even ...
18
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5answers
28k views

The Time That 2 Masses Will Collide Due To Newtonian Gravity [closed]

My friend and I have been wracking our heads with this one for the past 3 hours... We have 2 point masses, $m$ and $M$ in a perfect world separated by radius r. Starting from rest, they both begin to ...
47
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17answers
175k views

How can momentum but not energy be conserved in an inelastic collision?

In inelastic collisions, kinetic energy changes, so the velocities of the objects also change. So how is momentum conserved in inelastic collisions?
21
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8answers
16k views

Would it help if you jump inside a free falling elevator?

Imagine you're trapped inside a free falling elevator. Would you decrease your impact impulse by jumping during the fall? When?
17
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4answers
2k views

Can black holes actually merge?

If time stops at the event horizon, can we ever detect two black holes merging? In other words, if you are a short distance away, would you encounter a spherically symmetric gravitational field, or a ...
12
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4answers
9k views

Could we use particle colliders as fusion generators?

So I know the basic gist is that fusion power's main issue is sustaining the fusion. I also know that there are two methods. The Torus method and the laser method. The torus magnetically contains ...
4
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2answers
11k views

What is the relative speed of two near-light speed particles headed towards each other? [duplicate]

I understand that nothing can move faster than light due to time dilation. I want to build upon my understanding of Einstein's theory of Special Relativity, so I came up with this hypothetical problem ...
1
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2answers
2k views

Elastic collision between two circles [duplicate]

I am trying to calculate the final velocities of two equal mass 2-dimensional circles after an elastic collision. I have tried to figure it out using formulas I know from high school physics, but ...
28
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7answers
127k views

Is two cars colliding at 50mph the same as one car colliding into a wall at 100 mph?

I was watching a youtube video the other day where an economist said that he challenged his physics professor on this question back when he was in school. His professor said each scenario is the same, ...
6
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3answers
3k views

Why are ions and electrons at different temperatures in a plasma?

In plasmas, the collision rate among ions or electrons is much larger than the collision rate between ions and electrons. Why is that so?
7
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2answers
2k views

Physics of simple collisions

I'm building a physics simulator for a graphics course, and so far I have it implementing gravitational and Coulomb forces. I want to add collisions next, but I'm not exactly sure how to go about ...
2
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4answers
858 views

Off-center impulse equations [closed]

A rigid steel bar with mass $M$ is hit sideways (very close to its end) by a steel ball with mass $m$ and velocity $v$. What are the equations of motion after elastic impact and how about conservation ...
34
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6answers
23k views

Newton's cradle

Why, when one releases 2 balls in Newton's cradle, two balls on the opposite side bounce out at approximately the same speed as the 1st pair, rather than one ball at higher speed, or 3 balls at lower ...
6
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3answers
1k views

Can linear momentum be conserved before and after collision in the presence of an external force?

I'm a physics tutor for 11th and 12th grade students. I taught my students that momentum is conserved only when the net external force on the system is zero. But in the books we are following, ...
2
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3answers
2k views

Determine resultant velocity of an elastic particle-particle collision in 3d space

So I have two particles that have collided in 3 dimensional space. I want the particles to rebound off of each other in an elastic manner. How do I determine the resultant velocity vector if I know: ...
14
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10answers
4k views

How to explain independence of momentum and energy conservation in a 2-body collision in elementary terms?

I'm trying to explain to someone learning elementary physics (16 year old) that linear momentum and energy are conserved independently in a 2-body collision. I'm not a professional physicist and haven'...
10
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5answers
4k views

Elastic collision of point particle and rod

A 1 meter long rod on the ice with mass $m_2=1$ kg is perpendicularly hit on one end by a point particle with mass $m_1=0.1$ kg. The collision is elastic and the point particle is bounced back in the ...
3
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3answers
4k views

Classical car collision [duplicate]

I have a very confusing discussion with a friend of mine. 2 cars ($car_a$ and $car_b$) of the same mass $m$ are on a collision course. Both cars travel at $50_\frac{km}{h}$ towards each other. They ...
7
votes
1answer
661 views

How and why will the Milky Way collide with the Andromeda galaxy?

Hubble's law says that the universe is expanding. How come the Milky Way and the Andromeda galaxies are on a collision course? How will they end up colliding with each other?
4
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1answer
10k views

Collisions between an object and a wall

Is momentum conserved when an object bounces back against a wall? The wall doesn’t move, but the object moves in the opposite direction. Assume this is an ideal, elastic collision. If, initially, the ...
0
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4answers
3k views

Can momentum be conserved in a perfectly elastic collision?

I am taking for granted that when we say that something is conserved it is understood 'in its full integrity'. Energy is represented by a scalar J, and is conserved in elastic collision. momentum ...
5
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2answers
3k views

What would the effect be of a small black hole colliding with the earth?

If a small black hole (say about .1 mm radius or 1% of Earth's mass) came flying along at the speed of a comet or higher and impacted the earth, what would happen? Would it pass through the earth (and ...
1
vote
1answer
293 views

Where can I find the equations for “quasi” elastic collisions?

Yes, you all talk about neutrinos and spins, but I came out with this basic s**t :D All of us learnt the basic equations of collisions, elastic (everything bounces and energy remains the same), or ...
9
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8answers
10k views

Collision of a black hole & a white hole

A black hole and white hole experience a direct collision. What happens? What shall be the result of such a collision?
15
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3answers
17k views

What happens in electron-electron collisions?

What are the results of high energy electron electron collisions? Are other particles created?
9
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1answer
16k views

Can a bullet shot through a glass make a clean hole?

One can often see (hopefully only in the movies) that a bullet shot through a pane of window glass leaves a hole in it, but overall the glass is left largely intact. However, a low-speed projectile, e....
17
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6answers
4k views

What would happen if Large Hadron Collider would collide electrons?

After some reading about the Large Hadron Collider and it's very impressive instruments to detect and investigate the collision results, there is a remaining question. What would happen if the ...
4
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5answers
30k views

Conservation of momentum but not kinetic energy in inelastic collisions

In inelastic collisions, the kinetic energy of the system is not conserved but the momentum is. Kinetic energy is: $0.5 \times \text{mass} \times \text{velocity}^2$. Momentum is: $\text{mass}\times\...
1
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1answer
104 views

How do I handle elastic contacts in a simulation with friction [closed]

I'm trying to simulate a wheel as it hits the ground. Problem 1 Suppose a disc is dropped from a height. It has initial velocity of $-x,-y$ caused by throwing and gravity. It has no initial angular ...
2
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5answers
5k views

What causes damage, kinetic energy or momentum?

Let's assume we have 2 bullets. The first bullet has $450$ $J$ of KE and $3$ $kg.m/s$ of momentum, while the second bullet has $250$ $J$ of KE and $5$ $kg.m/s$. Now if they are both shot at ballistic ...
2
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2answers
1k views

Newton's Cradle: why does it stay symmetric? [duplicate]

How is it that always the same number of balls leave at the other end in Newton's cradle. I understand that the momentum needs to be conserved, but as momentum is defined as p=m*v couldn't you have a ...
1
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4answers
144 views

Please help understanding the difference between force and kinetic energy for an object hitting a wall?

If a car hits a wall at a speed of $v$, and an identical car hits a wall at a speed of $2\,v$, with the kinetic energy equation $E_K = \frac{1}{2}mv^2$ (the speed goes from $v$ to $0$) the second car ...
1
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3answers
10k views

Why is there conservation of kinetic energy in elastic collision and not in inelastic collision?

Why is there conservation of kinetic energy in elastic collision and not in inelastic collision? What would be the difference that lead to conservation of kinetic energy in elastic collision and not ...
50
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6answers
12k views

Why don't all objects bounce like rubber balls?

Some things don't bounce like rubber balls do. For example, books don't bounce much when dropped. Why is it that some things bounce while others don't?
13
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4answers
1k views

Formalism to deal with discontinuous potentials in classical mechanics (hard wall, hard spheres)

It seems to me that Hamiltonian formalism does not suit well for problems involving instantaneous change of momentum, like particle collisions with hard wall or hard sphere gas model. At least I could ...
8
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2answers
1k views

How multiple objects in contact are resolved in an inelastic collision, when edge normals don't “line up”

In a case I understand, let's say I have an object A moving at velocity V toward 3 objects in contact B, C, and D: The momentum of A is the mass of A times its velocity. To figure out how the ...
6
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2answers
4k views

Is there a 2D generalization of the coefficient of restitution?

The coefficient of restitution characterizes a collision in one dimension by relating the initial and final speeds of the particles involved, $$C_R = -\frac{v_{2f} - v_{1f}}{v_{2i} - v_{1i}}$$ In a ...
5
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3answers
1k views

Multiple colliding balls

I have written an algoritm to resolve a collision between two balls with conservation of momentum. It looks to work exactly as expected in my simulations. Here is the code: ...
15
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6answers
7k views

Why doesn't Newton's third law mean a person bounces back to where they started when they hit the ground? [closed]

Why doesn't a person bounce back after falling down like a ball does? If we push a person and he falls down then why doesn't he come back to his initial position? According to Newton's 3rd law of ...
8
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3answers
12k views

Number of planks required to stop the bullet [closed]

A bullet looses (1/n)th of its velocity passing through one plank. The number of such planks that are required to stop the bullet can be? Logically, to me the answer seems to be infinity, as always a ...
4
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1answer
3k views

Are there perfect elastic collisions in Nature?

Can we find at any level, molecules, atoms, particles etc., a perfect elastic collision? If not, what is second best? EDIT: At macroscopic level what is the most elastic material and the highest CoR ...
4
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3answers
1k views

Why is the laboratory frame energy always greater than the center of mass frame energy?

I have been looking for an answer to 'Why is the laboratory frame energy always greater than the center of mass frame energy during collisions?'. A lot of resources provided mathematical explanations....
2
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2answers
493 views

Are relativistic momentum and relativistic mass conserved in special relativity?

Suppose two objects collide and combine into a single object, will the total relativistic momentum and relativistic mass stay the same? I read in my grade 12 physics text book that relativistic ...
1
vote
1answer
480 views

Is my method here for solving this 1D 3-body collision problem correct?

I was attempting to solve a three body problem which I made up that goes like this: The diagram shows their velocities and masses just before collision. The coefficient of restitution between each ...
3
votes
2answers
255 views

Does inelastic collision say the ball bounces back to you when thrown at an angle on ground?

I created a bounce simulation using exactly the formula from Wikipedia. The behavior I observe is not what I would expect in two cases: When two balls hit off-centre, they act the same as if the ...
2
votes
1answer
1k views

How to get the new direction of 2 disks colliding?

I'm developing a 2D game including collisions between many disks. I would like to know how I can get the angle corresponding to the new direction of each disk. For every disk I have this information :...
0
votes
2answers
156 views

What work is done by the wall when a ball hits it?

So, in my physics textbook it's written that the kinetic energy possessed by a body is equal to the amount of work done by an opposing force to stop the body, now that got me thinking that when a ball ...
43
votes
6answers
16k views

Newton's 3rd law… hitting drywall (which I break) vs hitting a brick (which breaks me)?

According to the Third Newton's law of motion: For every action there is an equal and opposite reaction. So, I understand that if I hit a brick wall with $50\, \mathrm{lbs}$ of force, the brick ...
42
votes
4answers
9k views

What would happen if Jupiter collided with the Sun?

This question is inspired by a similar one asked on Quora. Let's say a wizard magicked Jupiter into the Sun, with or without high velocity. What happens? The Quora question has two completely opposed ...
7
votes
7answers
4k views

Why isn't momentum conserved in this pulley problem?

I have some conceptual doubt about method of solving this problem. 24. A block of mass $m$ and a pan of equal mass are connected by a string going over a smooth light pulley as shown in figure (9-...