{"id":427,"date":"2017-08-23T06:09:14","date_gmt":"2017-08-23T06:09:14","guid":{"rendered":"http:\/\/americanboard.org\/Subjects\/elementary-education\/?page_id=427"},"modified":"2017-09-25T16:04:48","modified_gmt":"2017-09-25T16:04:48","slug":"principles-of-motion-and-energy","status":"publish","type":"page","link":"https:\/\/americanboard.org\/Subjects\/elementary-education\/principles-of-motion-and-energy\/","title":{"rendered":"Principles of Motion &#038; Energy"},"content":{"rendered":"<div class=\"twelve columns\" style=\"margin-top: 10%;\">\n<div class=\"advance\"><a class=\"button button-primary\" href=\"http:\/\/americanboard.org\/Subjects\/elementary-education\/structure-and-properties-of-matter\">\u2b05 Previous Lesson<\/a>\u00a0<a class=\"button\" href=\"http:\/\/americanboard.org\/Subjects\/elementary-education\/physical-science-scientific-investigation\">Workshop Index<\/a>\u00a0<a class=\"button button-primary\" href=\"http:\/\/americanboard.org\/Subjects\/elementary-education\/electricity-and-magnetism\">Next Lesson \u27a1<\/a><\/div>\n<p><!-- CONTENT BEGINS HERE --><\/p>\n<h1 id=\"title\">Principles of Motion &amp; Energy<\/h1>\n<h4>Objective<\/h4>\n<p>In this section, we will delve into and review some ideas about motion, force, and energy.<\/p>\n<h4>Previously Covered:<\/h4>\n<ul>\n<li>In the previous lessons, we reviewed solutions, chemical reactions, and chemical equilibrium. We also examined a few types of bonds and talked about predicting certain reactions.<\/li>\n<\/ul>\n<section>\n<h3>Force and Motion<\/h3>\n<p><abbr title=\"A vector quantity that produces an acceleration of a body.\">Force<\/abbr> and motion are intimately intertwined concepts because a force is required to change an object&#8217;s motion. To get anywhere in understanding concepts in motion, you must first understand the terminology. Be careful here. As is typical in science, familiar words are used with very specific meanings that are different from their everyday meanings. Don&#8217;t assume that because a word is familiar that you know its meaning in this context.<\/p>\n<h3>What is the Difference between Speed and Velocity?<\/h3>\n<p><abbr title=\"A measure of the rate of motion (the distance traveled divided by the time of travel).\">Speed<\/abbr> and <abbr title=\"An object\u2019s speed in a certain direction.\">velocity<\/abbr> are not the same thing even though they are often used as interchangeable terms. The basic difference is that velocity includes the direction of motion while speed does not. When you are driving, the speed of your car might be 50 miles per hour; its velocity might be 50 miles per hour towards the east. If in the same situation we look at your velocity toward the north, the result is very different. The speed of the car is still 50 miles per hour, but your velocity is zero! The reason for this is that the direction part of the velocity is all toward the east and nothing is directed toward the north. Velocity requires both the magnitude AND a direction.<\/p>\n<p>An <abbr title=\"A change in velocity.\">acceleration<\/abbr> is a change in the velocity over a period of time. Specifically, acceleration is defined as the time rate change of velocity (a = v\/t). You may be used to thinking of accelerating as speeding up, but it also includes slowing down and changing direction. Like velocity, the acceleration is a <abbr title=\"A vector is any quantity, like velocity and acceleration, that includes both a magnitude and a direction. A quantity like speed, which includes only a magnitude but not the direction, is called a scalar.\">vector<\/abbr> quantity that also includes the direction. An acceleration perpendicular to the velocity will change the direction of the velocity without changing the speed.<\/p>\n<p>Acceleration, velocity, and speed are all rates of change. Velocity and speed measure the rate at which the position changes, while acceleration measures the rate at which the velocity changes.<\/p>\n<p>Hence the <abbr title=\"average speed = distance\/time or V&lt;sub&gt;average&lt;\/sub&gt;\">average speed<\/abbr> over an interval is defined as the change in position, or displacement, during that time. If it takes you an hour to drive to a town 50 miles away, your average speed will be 50 miles per hour. If the town is east of your home, your average velocity will be 50 miles per hour towards the east.<\/p>\n<p>The <abbr title=\"average acceleration = change in velocity\/change in time or A&lt;sub&gt;average&lt;\/sub&gt;.\">average acceleration<\/abbr> is defined in a similar way. It is the change in velocity during a time interval divided by the time interval.<\/p>\n<section class=\"question\">\n<h4>Question<\/h4>\n<p>If a 2,500-mile cross country flight takes 5 hours, what is the average speed of the plane?<\/p>\n<ol>\n<li>12,500 miles per hour<\/li>\n<li>2,000 miles per hour<\/li>\n<li>500 miles per hour<\/li>\n<li>200 miles per hour<\/li>\n<\/ol>\n<p><a class=\"q-answer button button-primary\">Reveal Answer<\/a><\/p>\n<p class=\"q-reveal\">The correct answer is C, 500 miles per hour. The average speed is the distance divided by the time or 2,500 miles divided by 5 hours.<\/p>\n<\/section>\n<h3>How are Velocity and Acceleration Represented Graphically?<\/h3>\n<p>Both can be represented on a graph as the slope of a line. On a graph with time as the x-axis (horizontal) and position as the y-axis (vertical), a constant velocity will be represented by a straight line, and the <abbr title=\"rise\/run or change in y\/change in x\">slope<\/abbr> will be the value of the velocity or speed. A steeper slope indicates a higher velocity. If the line is curved, then the velocity is changing. In a similar fashion, a graph with velocity as the y-axis and time as the x-axis will show the acceleration.<\/p>\n<h3>What Causes Acceleration?<\/h3>\n<p>In order to have acceleration, there must be an unbalanced force applied to an object. This statement is the essential meaning of <abbr title=\"When no force acts on an object (or when the forces acting on it cancel), it moves in a straight line at constant speed.\">Newton&#8217;s first law<\/abbr>. If there are no unbalanced forces acting on an object, that doesn&#8217;t mean the object is at rest. The object could be moving at a constant velocity. Macroscopic forces that we experience include gravity, friction, electromagnetic forces, and contact forces such as pushing on a surface.<\/p>\n<p>Think about the following:<\/p>\n<p>A box is sliding across the floor. When you stop pushing the box\u2014applying a force\u2014the box slows to a stop because<\/p>\n<ul>\n<li>there is no longer a force acting on the box.<\/li>\n<li>air resistance slows the box down.<\/li>\n<li>an object can move only when a force is acting on it.<\/li>\n<li>the friction from the floor acts on the box against its motion to change its velocity.<\/li>\n<\/ul>\n<p>Friction is the key here.<\/p>\n<p>Objects do not need to have force acting on them in order to keep moving. They only need the force to accelerate them (change their velocity). The frictional force of the floor accelerates the box in the direction opposite its velocity, so it slows to a stop.<\/p>\n<h3>How is Pressure Related to Force?<\/h3>\n<p>Pressure is force divided by area. A sharp knife cuts food more easily than a dull one because with a sharp knife the same force is applied to a smaller area. Hence you can exert more pressure with a sharp knife than a dull one. We also feel pressure from air, water, and other fluids. This pressure increases with depth. So atmospheric pressure at sea level is greater than on a mountaintop. Similarly, when we dive to the bottom of a swimming pool, we feel a greater water pressure at a greater depth.<\/p>\n<h3>Review<\/h3>\n<ul>\n<li>Velocity includes the direction of motion while speed does not.<\/li>\n<li>A constant velocity is represented by a straight line on a graph, and the slope will be the value of the velocity or speed. A steeper slope indicates a higher velocity.<\/li>\n<li>Newton\u2019s first law: When no force acts on an object (or when the forces acting on it cancel), it moves in a straight line at constant speed.<\/li>\n<\/ul>\n<\/section>\n<p><!-- CONTENT ENDS HERE --><\/p>\n<div class=\"advance\"><a class=\"button button-primary\" href=\"http:\/\/americanboard.org\/Subjects\/elementary-education\/structure-and-properties-of-matter\">\u2b05 Previous Lesson<\/a>\u00a0<a class=\"button\" href=\"http:\/\/americanboard.org\/Subjects\/elementary-education\/physical-science-scientific-investigation\">Workshop Index<\/a>\u00a0<a class=\"button button-primary\" href=\"http:\/\/americanboard.org\/Subjects\/elementary-education\/electricity-and-magnetism\">Next Lesson \u27a1<\/a><\/div>\n<p><a class=\"backtotop\" href=\"#title\">Back to Top<\/a><\/p>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>\u2b05 Previous Lesson\u00a0Workshop Index\u00a0Next Lesson \u27a1 Principles of Motion &amp; Energy Objective In this section, we will delve into and review some ideas about motion, force, and energy. Previously Covered: In the previous lessons, we reviewed solutions, chemical reactions, and chemical equilibrium. We also examined a few types of bonds and talked about predicting certain [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-427","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/americanboard.org\/Subjects\/elementary-education\/wp-json\/wp\/v2\/pages\/427","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/americanboard.org\/Subjects\/elementary-education\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/americanboard.org\/Subjects\/elementary-education\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/americanboard.org\/Subjects\/elementary-education\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/americanboard.org\/Subjects\/elementary-education\/wp-json\/wp\/v2\/comments?post=427"}],"version-history":[{"count":11,"href":"https:\/\/americanboard.org\/Subjects\/elementary-education\/wp-json\/wp\/v2\/pages\/427\/revisions"}],"predecessor-version":[{"id":1363,"href":"https:\/\/americanboard.org\/Subjects\/elementary-education\/wp-json\/wp\/v2\/pages\/427\/revisions\/1363"}],"wp:attachment":[{"href":"https:\/\/americanboard.org\/Subjects\/elementary-education\/wp-json\/wp\/v2\/media?parent=427"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}