Lecture 4

Lecture 4 - PHYS 172 Modern Mechanics Fall 2007 CLICKER...

This preview shows pages 1–3. Sign up to view the full content.

1 Fall 2007 PHYS 172: Modern Mechanics Lecture 4 – Conservation of Momentum Read 2.7–2.14 CLICKER QUESTION #1 Reading Question (Sections 2.7 – 2.14) (This is a closed-book quiz, no consulting with neighbors, etc.) Which of the following are always conserved? A. The total velocity of a system B. The total momentum of a system C. The total momentum of a system + the total momentum of its surroundings D. The sum of the forces acting on a system E. The total momentum of a non-rotating system Important topics for today: • More on the momentum principle • Impulse • Reciprocity • More than one particle in a system • Conservation of momentum t F p p net i f ! + = ! ! ! KEY EQUATIONS t v r r ave i f ! + = ! ! ! position update formula momentum principle Impulse : For a short time interval, t F ! " ! Impulse So, the change in momentum of an object is equal to the net impulse applied to it. ! ! p = ! F net ! t = Impulse Applying the Momentum Principle (p. 46) 1. Choose a system (some portion of universe). Rest of universe is called surroundings. 2. List objects in surroundings that have significant influence on system; make appropriate diagrams 3. Choose initial and final times 4. Apply the momentum principle to the chosen system: Substitute known values into the terms of the momentum principle. Use position update if needed. 5. Check units and reasonableness of your answer t F p p net i f ! + = ! ! !

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
2 A) p x B) p y C) p z D) p x & p y E) p x , p y , & p z A ball is initially at rest on the ground, and you kick it so it has an initial velocity < 3,7,0> m/s. At this speed air resistance is negligible. Assume the usual coordinate system. Which components of the ball's momentum will change in the next half second? Which graph correctly shows p y for the ball during this 0.5 s? E D C B A The initial momentum of the ball was < 1.5, 3.5, 0 > kg*m/s. The final momentum after 0.5 s of the ball is < 1.5, 1.05, 0 > kg*m/s. Reciprocity : if you push on a spring, the spring pushes back on you (at the same time). These two forces are equal in magnitude, opposite in direction, and act on different objects . This reciprocity property is a feature of all electric and gravitational forces (which describes most everything we’ll be dealing with).
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

• As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

Kiran Temple University Fox School of Business ‘17, Course Hero Intern

• I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

Dana University of Pennsylvania ‘17, Course Hero Intern

• The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

Jill Tulane University ‘16, Course Hero Intern