Forces and Motion, Third Edition

Amy Graves, Sophia Chen

Description

The term motion means a change in the position of a body with respect to time, as measured by a particular observer in a particular frame of reference. Until the end of the nineteenth century, Isaac Newton's laws of motion, which he posited as axioms or postulates in his famous Principia, were the basis of what has since become known as classical physics.

Filled with full-color and detailed figures, Forces and Motion, Third Edition explores these scientific topics and looks at how physics, through simple and general concepts, affects the way people live and how the world around them works. Each chapter focuses on a single aspect of force and motion, explaining these laws in accessible terms of the modern world.

Sujets

• Sciences et techniques
• Outline of physical science
• Physics
• Research
• Motion
• Velocity
• Discovery
• Science
• Physique
• Physical attractiveness

Informations

• Publié par: Infobase Publishing
• Date de parution: 01 septembre 2021
• Nombre de lectures: 0
• EAN13: 9781646937349
• Langue: English
• Poids de l'ouvrage: 1 Mo

Extrait

Forces and Motion, Third Edition
Copyright © 2021 by Infobase
All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage or retrieval systems, without permission in writing from the publisher. For more information, contact:
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ISBN 978-1-64693-734-9
You can find Chelsea House on the World Wide Web at http://www.infobase.com
Contents Chapters The Science of Machines and More Speed and Distance Calculation Speed and Acceleration Motion in Three Dimensions Accelerated Motions Forces Forces and Accelerations Support Materials Glossary Bibliography About the Authors Index
Chapters
The Science of Machines and More

The term physics comes from a Greek word that means "knowledge of nature." Physicists are people who study the natural world. The way that physicists have built up their rich knowledge is by combining hands-on experience, philosophical thinking, and mathematics. Throughout history, the invention of new technology has sparked progress in physics by enabling game-changing observations. In addition, developments in pure mathematics have also opened doors to new physics by offering new ways to organize and analyze experimental results.
This text is about force and motion, which is a subfield of physics called mechanics. Mechanics is the oldest branch of physics, in the sense that it was the first one to be put in a form that is fairly complete and recognizable today. The term mechanics refers to machines. (Today we would say that someone who studies machines is a mechanical engineer.) Before the fifteenth century, people had only scarce knowledge of basic science to guide their design of early machines, such as the wind and water mills to grind grain, or the cranes used to build Europe's cathedrals. The new science of mechanics explained, for example, how these machines decrease the amount of force a person has to exert to perform a task, or how they change one form of motion into another. This deeper understanding thus helped people improve the workings of these classic machines.
Thinkers also wanted to understand the great "machine" in the sky: the motion of the planets and stars. People have studied "celestial mechanics" throughout the world since the start of recorded history. More than 3,000 years ago, Babylonian scholars compiled detailed records of the positions of the Sun, Moon and stars. However, they could not make very accurate predictions. In the fifteenth century and onward, scholars wanted to knit their observations into a theory. A theory would allow them to deduce new facts and make predictions. For example, if you saw a new planet and charted its position over many nights, a theory of planetary motion could allow you to deduce its distance from Earth and predict its motion for years to come.
Theories often evolve to explain new experimental results or observations. Occasionally, this may lead physicists to throw out a previously established theory. Around A.D. 100, the Egyptian scholar Ptolemy compiled data from earlier observations and combined it with a theory that predicted how the celestial machine would evolve. Unfortunately, scholars later realized that Ptolemy's theory contained a glaring error that placed the Earth at the center of the universe, with the Sun and everything else in the cosmos orbiting around it.
We generally credit Nicolaus Copernicus with first proposing the theory that the Earth moves around the Sun in his work On the Revolution of Heavenly Spheres in 1543. This theory challenged the prevailing orthodoxy of the Roman Catholic Church, and led to his work being placed on a list of forbidden books in 1616. A prohibition on Copernicus's theory remained in effect until 1753, and his original work was not removed from the forbidden book list until 1835. 1
Still Copernicus's theory was incomplete. He thought the Sun was fixed at the center of the universe. Using his ideas as a starting point, physicists later understood that the Sun also moves around the center of our galaxy, the Milky Way, which is just one of the estimated hundreds of billions of galaxies in the universe. 2

Nicolaus Copernicus (1473–1543) was the astronomer who formulated the first heliocentric (sun-centered) theory of the solar system, in which the Earth spins once every 24 hours about an internal axis, while at the same time making a complete trip around the Sun once every 365 days.
Kinematics and Dynamics
The name kinematics comes from a Greek word that means "the study of motion." Johannes Kepler, born a few decades after Copernicus died, was apparently the first to correctly understand the kinematics of the planets. He found that they move, to a very good approximation, in orbits that are shaped like ellipses, with a certain relationship between their speed of motion and the size of the orbit. Sir Isaac Newton, who was born just a few years after Kepler died, later explained why this occurs. Newton gave us dynamics (from a Greek word that means "power"). Dynamics explains how force creates the kinematics that we observe. 3  Newton's theory of gravity predicted the planet Neptune, which was discovered in 1846. Prior to its discovery, people had observed Neptune's perturbing effects on the orbit of the planet Uranus, which was already known at that time. 4 In the twentieth century, astrophysicists like Vera Rubin have found that a large fraction of the stuff in our universe is "dark matter." 5 It does not shine like a star, planet, or gas cloud, with any known type of radiation. Physicists believe dark matter exists because of the detailed way that galaxies rotate around their centers. Some invisible type of matter is creating a force that has a very noticeable dynamic effect on the visible matter around it. 6
Many scholars contributed successfully to mechanics before and during Newton's time. While Newton's work builds on others' work, Newton was probably unique among these scholars in the way that he brought observation, philosophy, and mathematics together. It is a powerful synergy that physicists have aspired to ever since. Newton saw the unity between a rock falling from a tower and the Moon orbiting Earth. They really are two siblings in the same "family" of motions. Both are curves that come from solving a single equation: Force = (mass) × (acceleration). For both, the force is the pull of Earth's gravity. A physics book (this one is no exception) typically considers many situations and applies the same mathematical theory to all of them, showing the unity behind the apparent differences.
Roadmap for This Text
Chapters two through five deal with kinematics, while dynamics is discussed in chapters six and seven. Within each chapter you will find the words, math formulas, graphs, and pictures that are all familiar parts of the language of physics. They will take you through the beginning of the kind of mechanics course you might take in the last two years of high school or the first year of college. We do not get to the topics of angular momentum or energy. We also do not talk about Einstein's theories, which are needed for objects moving very swiftly (near the speed of light) and/or subject to very large forces (say, near a massive star).
Every chapter includes problems about motion or force. In chapter two, for example, you will find the average speed of kids hurrying down a long hallway to class. Examples illustrate the relationship between speed, time, and distance. The section introduces the concept of displacement to pave the way for understanding paths that do not necessarily lie along a straight line. In chapter three, you will learn how to solve problems in two different ways: by manipulating symbols and equations, or by using geometry. You can use both ways to solve problems about acceleration that involve a predator chasing its prey or an ecologist measuring the speed of water in a stream.
Chapter four discusses vectors, an essential mathematical tool for understanding the velocity of moving objects such as a plane. In that chapter, we represent vectors both with pictures and in terms of their components, and explore how to do algebra with them. We see how to use displacement, velocity, and acceleration vectors to fully understand interesting motion, and see how a simple accelerometer indicates the strength and direction of acceleration. The importance of acceleration continues in chapter five, where you will learn how to find the g-forces on a roller coaster. We explore examples like a geosynchronous satellite and a plane that must "touch and go" from a runway.
Chapter six discusses forces in the context of a science fiction scene in which someone is expelled into outer space. The example explores the nature of motion in the absence of any force (as when one is floating in space) in terms of Newton's first law and the concept of center-of-mass. The example also illustrates pressure forces, and how the human body balances Earth's atmospheric pressure to keep itself from imploding.
Finally, chapter seven presents Newton's second and third laws. Here, we introduce inertia, or mass, and the rule that an object feeling a force will experience an acceleration inversely proportional to its inertia. The section closes with an example that applies all three of Newton's laws and the vector nature of velocity, in order to understand the consequences of a collision between a deer and a vehicle.
1. Bald, Margaret. "Copernicus, Nicolaus" in Literature Suppressed on Religious Grounds , 4th ed. (New York: Infobase, 2019).
2. Howell, Elizbeth. "How Many Galaxies Are There?" Space.com, March 19, 2018. Available online. URL:  https://www.space.com/25303-how-many-galaxies-are-in-the-universe.html . Accessed August 1, 2021.
3. Gleick, James. Isaac Newton. (New Yor