Physics 7:1-4 Conservation of Momentum and Energy

Homework

Reading Preparation
Key Equations
WebLecture
Study Activity
Chat Preparation Activities
Chapter Quiz
Lab Work

Reading Preparation

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

Study Points

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 = F = >Δt = 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.

Key Equations

Definition of force in terms of momentum: $Σ \vec{F} = \frac{Δ \vec{p}}{Δ t} = m \vec{a}$
Change in momentum = Impulse $Δ \vec{p} = \vec{F} t$
Conservation of momentum in elastic collision $m_{A} v_{A} + m_{B} v_{B} = m_{A} {v^{'}}_{A} + m_{B} {v^{'}}_{B}$

Web Lecture

Read the following weblecture before chat: Momentum

Study Activity

Check out the Collision Cart Simulation at the Physics Classroom site. Change the masses and velocities for elastic collisions, then use the same variables to simulate inelastic collisions. Which combinations result in stopping one or the other cart as a result of the collision?

Chat Preparation Activities

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.

Chapter Quiz

The chapter quiz is not yet due.

Lab Work

If you want lab credit for this course, you must complete at least 18 labs; you may complete more if you are preparing for the AP exam.. 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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Physics

Chapter 7: 1-4 Assignment