Skip to ContentGo to accessibility page
OpenStax Logo
University Physics Volume 1

Summary

University Physics Volume 1Summary

Summary

9.1 Linear Momentum

  • The motion of an object depends on its mass as well as its velocity. Momentum is a concept that describes this. It is a useful and powerful concept, both computationally and theoretically. The SI unit for momentum is kg·· m/s.

9.2 Impulse and Collisions

  • When a force is applied on an object for some amount of time, the object experiences an impulse.
  • This impulse is equal to the object’s change of momentum.
  • Newton’s second law in terms of momentum states that the net force applied to a system equals the rate of change of the momentum that the force causes.

9.3 Conservation of Linear Momentum

  • The law of conservation of momentum says that the momentum of a closed system is constant in time (conserved).
  • A closed (or isolated) system is defined to be one for which the mass remains constant, and the net external force is zero.
  • The total momentum of a system is conserved only when the system is closed.

9.4 Types of Collisions

  • An elastic collision is one that conserves kinetic energy.
  • An inelastic collision does not conserve kinetic energy.
  • Momentum is conserved regardless of whether or not kinetic energy is conserved.
  • Analysis of kinetic energy changes and conservation of momentum together allow the final velocities to be calculated in terms of initial velocities and masses in one-dimensional, two-body collisions.

9.5 Collisions in Multiple Dimensions

  • The approach to two-dimensional collisions is to choose a convenient coordinate system and break the motion into components along perpendicular axes.
  • Momentum is conserved in both directions simultaneously and independently.
  • The Pythagorean theorem gives the magnitude of the momentum vector using the x- and y-components, calculated using conservation of momentum in each direction.

9.6 Center of Mass

  • An extended object (made up of many objects) has a defined position vector called the center of mass.
  • The center of mass can be thought of, loosely, as the average location of the total mass of the object.
  • The center of mass of an object traces out the trajectory dictated by Newton’s second law, due to the net external force.
  • The internal forces within an extended object cannot alter the momentum of the extended object as a whole.

9.7 Rocket Propulsion

  • A rocket is an example of conservation of momentum where the mass of the system is not constant, since the rocket ejects fuel to provide thrust.
  • The rocket equation gives us the change of velocity that the rocket obtains from burning a mass of fuel that decreases the total rocket mass.
PreviousNext
Order a print copy
Citation/Attribution
Reuse and redistribution of this content in digital or print format:
  • This book may not be used in the training of large language models or otherwise be ingested into large language models or generative AI offerings without OpenStax's prior written permission.
  • This book uses the Creative Commons Attribution-NonCommercial-ShareAlike License, which means that you can reuse and modify the material only for noncommercial purposes, must attribute OpenStax, and must distribute any derivative works under the same license.
  • Any commercial printing of this textbook, including using a local or custom printer, must be approved by OpenStax, and proper citation provided.
  • OpenStax-copyrighted images, activities, assessments, and similar components of this book are subject to the same licensing – CC-BY-NC-SA. They can be used for noncommercial purposes with attribution. Commercial use requires permission.
  • Permission requests: Anyone who intends to incorporate this content (including text, images, and other components) into large language models, use it in AI offerings, use it commercially (including in print), and/or has questions about another use case is welcome to complete our reuse request form.
Attribution information
  • If you are redistributing all or part of this book in a noncommercial print format, then you must include on every physical page the following attribution:

    Access for free at https://openstax.org/books/university-physics-volume-1/pages/1-introduction

  • If you are redistributing all or part of this book in a noncommercial digital format, then for every page that includes OpenStax content, you must license the derivative work under the same CC-BY-NC-SA license as the original, and include on every digital page view the following attribution:

    Access for free at https://openstax.org/books/university-physics-volume-1/pages/1-introduction

Citation information

The information below includes the information needed to generate citations in most major styles (APA, MLA, etc.); you must reformat and organize the information as needed to fit the requirements of the style. Use the information below to generate a citation. We recommend using a citation tool such as this one.

© Jun 11, 2026 OpenStax. Textbook content produced by OpenStax is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike License. The OpenStax name, OpenStax logo, OpenStax book covers, OpenStax CNX name, and OpenStax CNX logo, and Rice University name, and Rice University logo trademarks, or wordmarks are not subject to the Creative Commons license and may not be reproduced without the prior and express written consent of Rice University.