Physics 2211: Lecture 21

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Physics 2211 Lecture 21
Conservation Laws Momentum Impulse
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Conservation Laws
The most fundamental laws in physics are
about things that dont change!
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Conservation of Mass
mass is the same (conserved) before and after
any physical process
stoichiometry in chemical reactions
explosion of a firecracker
formation of the planets
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Conservation of Energy
We will learn that energy comes in various types

• Kinetic Energy
• Potential Energy
• Thermal Energy

Total (sum) energy is conserved in physical
processes.
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Conservation Laws in Physics
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MOMENTUM is very useful for analyzing COLLISIONS
Simulation of a collision between two buckyballs
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definition of momentum
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From the blue curve
does none of the above.
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Newtons 2nd Law
Impulse
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Note double subscript
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Chalk Time!
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Which blue vector best represents the impulse for
this situation?
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For each component separately, can use Momentum
Bar Charts
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A particle is at rest at t0. What is the
direction of the momentum vector when the forces
stop acting?
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Discussion The impulse required to bring the car
to a stop is the same in the two cases shown
below. Why is the amount of damage to the car so
different?
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Does the weight of an hourglass change when the
sand is falling?
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Therefore, the weight of each grain during its
free fall get counted as momentum
lost by some other grain when it hits the
pile.
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Recap
Conservation Laws Momentum Impulse
Next Lecture
Conservation of Momentum Section 9.3