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. Physics (Greek Physis - φύσις in everyday terms is the Science of Matter and its motion. In Classical mechanics, momentum ( pl momenta SI unit kg · m/s, or equivalently N · s) is the product

Contents 1 Dynamics 2 Billiards 3 Traffic 4 See also 5 External links

Dynamics

Collisions involve forces (there is a change in velocity). In Physics, velocity is defined as the rate of change of Position. 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. elastic collision is a collision in which the total Kinetic energy of the colliding bodies after collision is equal to their total kinetic energy before collision In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός In Classical mechanics, momentum ( pl momenta SI unit kg · m/s, or equivalently N · s) is the product An inelastic collision is a Collision in which kinetic energy is not conserved (see elastic collision)

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

The field of dynamics is concerned with moving and colliding objects. In physics the term dynamics customarily refers to the time evolution of physical processes

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. Rolling resistance, sometimes called rolling friction or rolling drag, is the resistance that occurs when a round object such as a ball or Tire Newton's laws of motion are three Physical laws which provide relationships between the Forces acting on a body and the motion of the 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). Traffic on Roads may consist of Pedestrians ridden or herded Animals Vehicles Streetcars and other Conveyances either singly Vehicles, derived from the Latin word vehiculum, are non-living Means of transport. The term person is used in Common sense to mean an individual Human being. For other uses of Object see Object. In Philosophy, an object is a thing an Entity, or a Being. It is an accident or even a disaster. An accident is a specific identifiable unexpected unusual and unintended external event which occurs in a particular time and place without apparent or deliberate A disaster is the impact of a natural or human-made hazard that negatively affects society or environment. At level crossings sometimes a train collides with a vehicle or person. The term level crossing (also called a railroad crossing, road through railroad, railway crossing, train crossing or grade crossing A train is a connected series of vehicles that move along a track ( Permanent way) to transport freight or passengers from one place to another 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. In Physics, velocity is defined as the rate of change of Position. Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object Driving is the controlled operation of a land Vehicle, usually a Motor vehicle such as a Truck or a car. 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. Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object

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. In Physical simulations Video games and Computational geometry, collision detection involves algorithms for checking for Collision, i elastic collision is a collision in which the total Kinetic energy of the colliding bodies after collision is equal to their total kinetic energy before collision An inelastic collision is a Collision in which kinetic energy is not conserved (see elastic collision) A mid-air collision is an aviation accident where two or more aircraft come into unplanned contact during flight Friction is the Force resisting the relative motion of two Surfaces in contact or a surface in contact with a fluid (e A projectile is any object propelled through space by the exertion of a force which ceases after launch Space debris or orbital debris, also called space junk and space waste are the objects in Orbit around Earth created by humans that no See also Impact crater An impact event is the Collision of a large Meteoroid, Asteroid or Comet (generically In the broadest sense the term impact crater can be applied to any depression natural or manmade resulting from the high velocity impact of a projectile with larger body Kinetic theory (or kinetic theory of gases) attempts to explain Macroscopic properties of Gases such as pressure temperature or volume by considering
• 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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