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Collision
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- the content below is remote from Wikipedia
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{{short description|Instance of two or more bodies physically contacting each other within a short period of time}}{{About|physics models|accidents|}}(File:Collision 9 Block.gif|alt=A 3D simulation demonstrating collision with a ball knocking over some blocks.|thumb|A 3D simulation demonstrating a collision with a ball knocking over some blocks)In physics, a collision is any event in which two or more bodies exert forces on each other in a relatively short time. Although the most common use of the word collision refers to incidents in which two or more objects collide with great force, the scientific use of the term implies nothing about the magnitude of the force.JOURNAL, Schmidt, Paul W., 2019, Collision (physics),weblink Access Science, en, 10.1036/1097-8542.149000, - the content below is remote from Wikipedia
- it has been imported raw for GetWiki
Types of collisions
File:Deflection.png|right|thumb|250px|Deflection happens when an object hits a plane surface. If the kinetic energy after impact is the same as before impact, it is an elastic collision. If kinetic energy is lost, it is an inelastic collision. The diagram does not show whether the illustrated collision was elastic or inelastic, because no velocities are provided. The most one can say is that the collision was not perfectly inelastic, because in that case the ball would have stuck to the wall.]]Collision is short-duration interaction between two bodies or more than two bodies simultaneously causing change in motion of bodies involved due to internal forces acted between them during this. Collisions involve forces (there is a change in velocity). The magnitude of the velocity difference just before impact is called the closing speed. All collisions conserve momentum. What distinguishes different types of collisions is whether they also conserve kinetic energy of the system before and after the collision. Collisions are of three types:- Perfectly inelastic collision. If most or all of the total kinetic energy is lost (dissipated as heat, sound, etc. or absorbed by the objects themselves), the collision is said to be inelastic; such collisions involve objects coming to a full stop. A "perfectly inelastic" collision (also called a "perfectly plastic" collision) is a limiting case of inelastic collision in which the two bodies coalesce after impact. An example of such a collision is a car crash, as cars crumple inward when crashing, rather than bouncing off of each other. This is by design, for the safety of the occupants and bystanders should a crash occur - the frame of the car absorbs the energy of the crash instead.
- Inelastic collision. If most of the kinetic energy is conserved (i.e. the objects continue moving afterwards), the collision is said to be elastic. An example of this is a baseball bat hitting a baseball - the kinetic energy of the bat is transferred to the ball, greatly increasing the ball's velocity. The sound of the bat hitting the ball represents the loss of energy. An inelastic collision is sometimes also called a plastic collision.
- Elastic collision If all of the total kinetic energy is conserved (i.e. no energy is released as sound, heat, etc.), the collision is said to be perfectly elastic. Such a system is an idealization and cannot occur in reality, due to the second law of thermodynamics.
Examples
Billiards
{{Anchor|Cue sports}}Collisions play an important role in cue sports. 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 zero-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 is an important fact that professional billiards players take into account,WEB, Alciatore, David G., January 2006,weblinkweblink" title="ghostarchive.org/archive/20221009weblink">weblink 2022-10-09, live, TP 3.1 90° rule, 2008-03-08, although it assumes the ball is moving without any impact of friction across the table rather than rolling with friction.Consider an elastic collision in two dimensions of any two masses m1 and m2, with respective initial velocities u1 and u2 where u2 = 0, and final velocities V1 and V2.Conservation of momentum gives m1u1 = m1V1 + m2V2.Conservation of energy for an elastic collision gives (1/2)m1|u1|2 = (1/2)m1|V1|2 + (1/2)m2|V2|2.Now consider the case m1 = m2: we obtain u1 = V1 + V2 and |u1|2 = |V1|2 + |V2|2.Taking the dot product of each side of the former equation with itself, |u1|2 = u1â¢u1 = |V1|2 + |V2|2 + 2V1â¢V2. Comparing this with the latter equation gives V1â¢V2 = 0, so they are perpendicular unless V1 is the zero vector (which occurs if and only if the collision is head-on).Perfect inelastic collision
missing image!
- Inelastischer stoÃ.gif -
a completely inelastic collision between equal masses
In a perfect inelastic collision, i.e., a zero coefficient of restitution, the colliding particles coalesce. It is necessary to consider conservation of momentum:
- Inelastischer stoÃ.gif -
a completely inelastic collision between equal masses
m_a mathbf u_a + m_b mathbf u_b = left( m_a + m_b right) mathbf v ,
mathbf v = frac{m_a mathbf u_a + m_b mathbf u_b}{m_a + m_b}
Animal locomotion
Collisions of an animal's foot or paw with the underlying substrate are generally termed ground reaction forces. These collisions are inelastic, as kinetic energy is not conserved. An important research topic in prosthetics is quantifying the forces generated during the foot-ground collisions associated with both disabled and non-disabled gait. This quantification typically requires subjects to walk across a force platform (sometimes called a "force plate") as well as detailed kinematic and dynamic (sometimes termed kinetic) analysis.Hypervelocity impacts
File:HRIV Impact.gif|thumb|Video of the hypervelocity impact of NASAâs Deep Impact probe on comet Tempel 1Tempel 1Hypervelocity is very high velocity, approximately over 3,000 meters per second (11,000 km/h, 6,700 mph, 10,000 ft/s, or Mach 8.8). In particular, hypervelocity is velocity so high that the strength of materials upon impact is very small compared to inertial stresses.BOOK, Critical technologies for national defense, Air Force Institute of Technology, 1991, AIAA, 1-56347-009-8, 287weblink Thus, metals and fluids behave alike under hypervelocity impact. An impact under extreme hypervelocity results in vaporize>vaporization of the impact force | and target. For structural metals, hypervelocity is generally considered to be over 2,500 m/s (5,600 mph, 9,000 km/h, 8,200 ft/s, or Mach 7.3). Meteorite impact crater>craters are also examples of hypervelocity impacts.See also{{colbegin}}
Notes{{Reflist}}References
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- content above as imported from Wikipedia
- "Collision" does not exist on GetWiki (yet)
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- "Collision" does not exist on GetWiki (yet)
- time: 3:02pm EDT - Sat, May 04 2024
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