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Elastic and Inelastic collisions

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Thanks much to Patrick M. Len for making these GIFs

Elastic collisions

Objects collide:

(a) without being deformed

(b) no kinetic energy (energy of motion) is lost

Example 1: Gas molecules bouncing off of each other

Example 2 Pool (pocket billiards )


Example 3 car bouncing off of a truck

Example 4: Two cars colliding, without any (apparent) deformation or heating



Inelastic Collisions

Objects collide:

(a) and parts are deformed

(b) much kinetic energy (energy of motion) is lost, and turned into heat

Example 5: car hitting a truck, and they stick together

Example 6: car hitting a truck, and they stick together


Partially elastic collisions

Objects collide:

(a) and are slightly deformed

(b) some kinetic energy (energy of motion) is lost, and turned into heat

Example 7: Cars bounce after a collision


How can we tell if a collision is elastic or not?

How can we tell if a collision is elastic or not? Taking into account kinetic energy (the energy of motion)

KE tr   =   KE translational

   = kinetic energy as stuff “translates”, or moves

Animations from http://waiferx.blogspot.com/2011/10/physics-presentation-collisions.html

Learning Standards

2016 Massachusetts Science and Technology/Engineering Curriculum Framework

HS-PS2-2. Use mathematical representations to show that the total momentum of a system of interacting objects is conserved when there is no net force on the system. Emphasis is on the qualitative meaning of the conservation of momentum and the quantitative understanding of the conservation of linear momentum in
interactions involving elastic and inelastic collisions between two objects in one
HS-PS2-3. Apply scientific principles of motion and momentum to design, evaluate, and refine a device that minimizes the force on a macroscopic object during a collision. Clarification Statement: Both qualitative evaluations and algebraic manipulations may be used.

Common Core Math

CCSS.MATH.CONTENT.7.EE.B.4 Use variables to represent quantities in a real-world or mathematical problem, and construct simple equations and inequalities to solve problems by reasoning about the quantities.
CCSS.MATH.CONTENT.8.EE.C.7 Solve linear equations in one variable
CCSS.MATH.CONTENT.HSA.SSE.B.3 Choose and produce an equivalent form of an expression to reveal and explain properties of the quantity represented by the expression. (including isolating a variable)
CCSS.MATH.CONTENT.HSA.CED.A.4 Rearrange formulas to highlight a quantity of interest, using the same reasoning as in solving equations. For example, rearrange Ohm’s law V = IR to highlight resistance R.

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