collision

1 (physics) an brief event in which two or more bodies come together; "the collision of the particles resulted in an exchange of energy and a change of direction" [syn: hit]

2 an accident resulting from violent impact of a moving object; "three passengers were killed in the collision"; "the collision of the two ships resulted in a serious oil spill"

3 a conflict of opposed ideas or attitudes or goals; "a collision of interests"

English

Pronunciation

• Rhymes: -ɪʒən

Noun

1. An instance of colliding.

Derived terms

• collision course
• collisional

Translations

French

Pronunciation

Noun

collision

1. An instance of colliding.

In physics, collision means the action of a system of bodies exchanging momentum during a period of time in which all external forces can be neglected.

Dynamics

Collisions involve forces (there is a change in velocity). Collisions can be elastic, meaning they conserve energy and momentum, inelastic, meaning they conserve momentum but not energy, or totally inelastic (or plastic), meaning they conserve momentum and the two objects stick together.

The magnitude of the velocity difference at impact is called the closing speed.

The field of dynamics is concerned with moving and colliding objects.

Billiards

In billiards, collisions play an important role. Because the collisions between billiard balls are nearly elastic, and the balls roll on a surface that produces low-rolling friction, their behavior is often used to illustrate Newton's laws of motion. After a low-friction collision of a moving ball with a stationary one of equal mass, the angle between the directions of the two balls is 90 degrees. This appears to be an important fact that many professional billiard players take into account.

Consider an elastic collision in 2 dimensions of any 2 masses m1 and m2, with respective initial and final velocities v1, V1 and v2, V2

Collision in the x Direction: m1v1 = m1V1cosΦ+m2V2cosθ

Collision in the y Direction: 0 = m1V1sinΦ-m2V2sinθ

Conservation of Energy for Elastic Collision: 1/2m1v12 = 1/2m1V12+1/2m2V22

Now consider the case m1 = m2, we then obtain 3 equations: 1. v12 = V12+V22. 2. v1 = V1cosΦ+V2cosθ. 3. 0 = V1sinΦ-V2sinθ.

So the vector v1=V1+V2.

The dot product of the vector v1 yields v1•v1 = V12+V22+2V1V2 = v12

Equation 1 tells us however that v12 = V12+V22 and so 2V1V2 = 0

Now, 2V1V2 = V1V2cos(θ+Φ) = 0 so cos(θ+Φ)=0 and θ+Φ=90°.

Traffic

In traffic such a collision can be between two vehicles, a vehicle and a person, a vehicle and an object, two persons or a person and an object (and more if an animal is involved). It is an accident or even a disaster. At level crossings sometimes a train collides with a vehicle or person. Due to the velocity and mass of a train it needs a long distance to stop, typically longer than the train driver can see ahead. When a train collides with a car this is more likely to be deadly for the people in the car than for those in the train, because the train has more mass and momentum.

See also

• Collision detection
• Car accident
• Elastic collision
• Inelastic collision
• Mid-air collision
• Friction
• Collision (physical attack)
• Projectile
• Space debris
• Impact event
• Impact crater
• Kinetic theory - collisions between molecules

External links

• Three Dimensional Collision - Oblique inelastic collision between two homogeneous spheres.
• Two Dimensional Collision - Java applet that simulates elastic collisions.
• One Dimensional Collision - One Dimensional Collision Flash Applet as well as theory behind it.

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