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**Text Reading**: Giancoli, *Physics - Principles with Applications*, Chapter 7: Sections 1-4

*Section 7.1*: Momentum is defined as the vector p = mv. Since v is a vector and is only multiplied the the scalar m, the result (momentum) must also be a vector. Force = ma = mΔv/Δt, which we can generalize to F = Δp/Δt.**Note:**Einstein realized that this formulation of force as "impulse" included the possibility that*mass*could change...and indeed it does when it is traveling at relativistic speeds.*Section 7.2*: Like energy, momentum in a system is*conserved*. The center of mass of the system, taken as a whole, cannot change unless acted on by an outside force. If individual parts of the system change their momentum (by changing direction or speed or mass), then the other parts of the system must change to compensate for this. This gives us a new tool for analyzing systems that include colliding particles that change speed and direction.*Section 7.3*: We can now define impulse by rewriting the momentum equation as*impulse*= FΔt = Δp. A force F applied to a body for a time Δt will change the momentum by Δp. The greater the force, or the longer the time, the greater the change in the momentum of the system affected by the force.*Section 7.4*: We now have**two**rules for changes to bodies, including bodies colliding with each other. Energy and momentum are both individually conserved, which gives us two**independent**rules for the system. Even though they involve m and v, each "law" can be applied by itself when we analyze a system.

- Definiion of force in terms of momentum: $$\Sigma \text{}\overrightarrow{F}\text{}=\text{}\frac{\Delta \overrightarrow{p}}{\Delta t}\text{}=\text{}m\overrightarrow{a}$$
- Change in momentume = Impulse $$\Delta \overrightarrow{p}\text{}=\text{}\overrightarrow{F}t$$
- Conservation of momentum in elastic collision $${m}_{A}{v}_{A}\text{}+{m}_{B}{v}_{B}\text{}=\text{}{m}_{A}{{v}^{\text{'}}}_{A}\text{}+\text{}{m}_{B}{{v}^{\text{'}}}_{B}\text{}$$

**Read the following weblecture before chat**: Momentum

Note: Adobe Flash is required for this simulation.

Change the masses of the balls to determine how mass changes momentum in collisions. Use the vector displays to determine the direction and relative sizes of velocity, momentum, and KE.

Physics simulation Java Applets are the product of the PHET Interactive Simulations project at the University of Colorado, Boulder.

**Forum question**: The Moodle forum for the session will assign a specific study question for you to prepare for chat. You need to read this question and post your answer**before**chat starts for this session.**Mastery Exercise**: The Moodle Mastery exercise for the chapter will contain sections related to our chat topic. Try to complete these before the chat starts, so that you can ask questions.

- The chapter quiz is not yet due.

If you want lab credit for this course, you must complete at least 12 labs (honors course) or 18 labs (AP students). One or more lab exercises are posted for each chapter as part of the homework assignment. We will be reviewing lab work at regular intervals, so do not get behind!

**Lab Instructions**: Lab: Collision Kinematics: Momentum

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