Lect04

Lect04 - PHYS 172 Modern Mechanics Spring 2012 Reminders 1...

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Spring 2012 PHYS 172: Modern Mechanics Reminders: 1. Please register your iClicker on CHIP a.s.a.p. We plan to transfer your iClicker scores to CHIP next week. 2. Homework due date extensions can only be requested before the official due date. Lecture 4 – Physical Models, Fundamental Interactions Read 2.7–2.8, 3.1-3.4 1

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Today •Poor Monkey •Reciprocity (Equal and Opposite Forces) xample olliding tudents •Example: Colliding Students •Four Fundamental Forces •Gravity… Lots of Gravity 2
Shoot the monkey Note : the trajectory is a parabola (if air friction is ignored) 3

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Reciprocity: Newton s 3d law F spring on mass Force magnitudes are the same Directions are opposite They act on different objects F mass on spring Reciprocity (Newton s 3 rd law): The forces of two objects on each other are always equal and are directed in opposite directions F spring on mass = - F mass on spring p = F net t NOTE: Velocity-dependent forces (e.g., magnetic forces) do not obey Newton s 3 rd law! 4
Physical models Spherical cow Ideal model: ignore factors that have no significant effect on the outcome 5

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Example: colliding students Mary and John are late for class and run into each other head-on. Q: Estimate the force that one student exerts on the other during collision
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Lect04 - PHYS 172 Modern Mechanics Spring 2012 Reminders 1...

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