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class="comp article-header-block mntl-block "><ul id="breadcrumbs_1-0" class="comp breadcrumbs mntl-universal-breadcrumbs mntl-block type--squirrel breadcrumbs" data-tracking-container="true"><li id="mntl-breadcrumbs__item_1-0" class="comp mntl-breadcrumbs__item mntl-block"><a href="https://www.thoughtco.com/sciences-math-4132465" rel="nocaes" id="mntl-text-link_5-0" class="mntl-text-link mntl-breadcrumbs__link" data-tracking-container="true" ><span class="link__wrapper">Science, Tech, Math</span></a> <span id="breadcrumbs__separator_1-0" class="comp breadcrumbs__separator mntl-text-block">›</span></li> <li id="mntl-breadcrumbs__item_2-0" class="comp mntl-breadcrumbs__item mntl-block"><a href="https://www.thoughtco.com/science-4132464" rel="nocaes" id="mntl-text-link_6-0" class="mntl-text-link mntl-breadcrumbs__link" data-tracking-container="true" ><span class="link__wrapper">Science</span></a> <span id="breadcrumbs__separator_2-0" class="comp breadcrumbs__separator mntl-text-block">›</span></li> <li id="mntl-breadcrumbs__item_3-0" class="comp mntl-breadcrumbs__item mntl-block"><a href="https://www.thoughtco.com/physics-4133571" rel="nocaes" id="mntl-text-link_7-0" class="mntl-text-link mntl-breadcrumbs__link" data-tracking-container="true" ><span class="link__wrapper">Physics</span></a> <span id="breadcrumbs__separator_3-0" class="comp breadcrumbs__separator mntl-text-block">›</span></li></ul> <div id="article-heading_1-0" class="comp article-heading mntl-article-header"> <h1 class="article-heading type--lion">What Speed Actually Means in Physics</h1> </div></div> </div><div class="loc article-post-header"><div id="post-header-social-block_1-0" class="comp post-header-social-block mntl-block"><div id="social-share-block_1-0" class="comp social-share-block mntl-block"><ul id="social-share_1-0" class="comp social-share mntl-social-share share" data-title="What Speed Actually Means in Physics" document="StructuredContentDocumentEx{parent=BaseDocumentEx{templateType=STRUCTUREDCONTENT, documentId=2699009, bestTitle='What Speed Actually Means in Physics'}}" data-description="When it comes to the physics of speed, how it is used and how does it differ from velocity? Simply put, speed is distance traveled per unit of time." data-tracking-container="true"> <li class="share-item share-item-facebook"> <span data-href="https://www.facebook.com/sharer/sharer.php?u=https%3A%2F%2Fwww.thoughtco.com%2Fspeed-2699009%3Futm_source%3Dfacebook.com%26utm_medium%3Dsocial%26utm_campaign%3Dsocial-share-article" data-network="facebook" data-click-tracked="true" class="share-link share-link-facebook" tabindex="0" title="Share on Facebook" aria-label="Share on Facebook" role="link"> <svg class="icon icon-facebook " > <use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#icon-facebook" href="#icon-facebook"></use> </svg> </span> </li> <li class="share-item share-item-flipboard"> <span data-href="https://share.flipboard.com/bookmarklet/popout?v=2&url=https%3A%2F%2Fwww.thoughtco.com%2Fspeed-2699009%3Futm_source%3Dflipit%26utm_medium%3Dweb%26utm_campaign%3Dwidgets%26utm_content%3Dwww.thoughtco.com&title=What+Speed+Actually+Means+in+Physics&t=1740000809322" 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srcset="https://www.thoughtco.com/thmb/tUE4rzV0xSv9kZSGYImfdLBG9qg=/1500x0/filters:no_upscale():max_bytes(150000):strip_icc()/GettyImages-843131716-5adca72504d1cf0037ae7dee.jpg 1500w" sizes="750px" alt="Light streaks going around a corner to represent speed." class=" primary-image__image mntl-primary-image--blurry" onload="(function(e){e.classList.add('loaded')})(this)" style="--blurry: url('data:image/gif;charset=utf-8;base64,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')" /> <noscript> <img src="https://www.thoughtco.com/thmb/tUE4rzV0xSv9kZSGYImfdLBG9qg=/1500x0/filters:no_upscale():max_bytes(150000):strip_icc()/GettyImages-843131716-5adca72504d1cf0037ae7dee.jpg" width="2121" height="1414" class="loaded primary-img--noscript primary-image__image 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He is the co-author of "String Theory for Dummies."" tabindex="0" data-inline-tooltip="true"> <a href="https://www.thoughtco.com/andrew-zimmerman-jones-2698607" rel="nocaes" data-trigger-link="true" class="mntl-attribution__item-name" tabindex="-1" >Andrew Zimmerman Jones</a> <div id="mntl-author-tooltip_1-0" class="comp mntl-author-tooltip mntl-tooltip mntl-group "> <div class="mntl-author-tooltip__top "> <div class="mntl-author-tooltip__image-wrapper"> <div class="img-placeholder" style="padding-bottom:122.8%;"> <img data-srcset="https://www.thoughtco.com/thmb/4SLRIZK8YpPtXA7rRAont_7XlZI=/40x0/filters:no_upscale():max_bytes(150000):strip_icc()/AZJFaceShot-56a72b155f9b58b7d0e783fa.jpg 40w, https://www.thoughtco.com/thmb/4to-l9l8Av3y1QsgGqdLcAFdsD8=/58x0/filters:no_upscale():max_bytes(150000):strip_icc()/AZJFaceShot-56a72b155f9b58b7d0e783fa.jpg 58w, https://www.thoughtco.com/thmb/Tq8yL6uL6OEQdP4_rE9q6Jef2T4=/76x0/filters:no_upscale():max_bytes(150000):strip_icc()/AZJFaceShot-56a72b155f9b58b7d0e783fa.jpg 76w, https://www.thoughtco.com/thmb/YLFbwe5OLwkvPlJ2ABiTMv9gdB4=/94x0/filters:no_upscale():max_bytes(150000):strip_icc()/AZJFaceShot-56a72b155f9b58b7d0e783fa.jpg 94w, https://www.thoughtco.com/thmb/zT3Rc7r-vVZqHGNKt46OJ9bEQps=/112x0/filters:no_upscale():max_bytes(150000):strip_icc()/AZJFaceShot-56a72b155f9b58b7d0e783fa.jpg 112w" data-sizes="80px" data-src="https://www.thoughtco.com/thmb/axvTF3y-VcI_2omF3XbmazaE7IU=/200x200/filters:no_upscale():max_bytes(150000):strip_icc()/AZJFaceShot-56a72b155f9b58b7d0e783fa.jpg" class="lazyload mntl-author-tooltip__image" width="200" height="200" /> <noscript> <img src="https://www.thoughtco.com/thmb/axvTF3y-VcI_2omF3XbmazaE7IU=/200x200/filters:no_upscale():max_bytes(150000):strip_icc()/AZJFaceShot-56a72b155f9b58b7d0e783fa.jpg" srcset="https://www.thoughtco.com/thmb/4SLRIZK8YpPtXA7rRAont_7XlZI=/40x0/filters:no_upscale():max_bytes(150000):strip_icc()/AZJFaceShot-56a72b155f9b58b7d0e783fa.jpg 40w, https://www.thoughtco.com/thmb/4to-l9l8Av3y1QsgGqdLcAFdsD8=/58x0/filters:no_upscale():max_bytes(150000):strip_icc()/AZJFaceShot-56a72b155f9b58b7d0e783fa.jpg 58w, https://www.thoughtco.com/thmb/Tq8yL6uL6OEQdP4_rE9q6Jef2T4=/76x0/filters:no_upscale():max_bytes(150000):strip_icc()/AZJFaceShot-56a72b155f9b58b7d0e783fa.jpg 76w, https://www.thoughtco.com/thmb/YLFbwe5OLwkvPlJ2ABiTMv9gdB4=/94x0/filters:no_upscale():max_bytes(150000):strip_icc()/AZJFaceShot-56a72b155f9b58b7d0e783fa.jpg 94w, https://www.thoughtco.com/thmb/zT3Rc7r-vVZqHGNKt46OJ9bEQps=/112x0/filters:no_upscale():max_bytes(150000):strip_icc()/AZJFaceShot-56a72b155f9b58b7d0e783fa.jpg 112w" alt="" width="200" height="200" class="img--noscript mntl-author-tooltip__image" /> </noscript> </div> </div> <div id="mntl-author-tooltip__name_1-0" class="comp mntl-author-tooltip__name mntl-attribution__item "> <a href="https://www.thoughtco.com/andrew-zimmerman-jones-2698607" rel="nocaes" class="mntl-attribution__item-name" tabindex="0" >Andrew Zimmerman Jones</a> </div> <span id="mntl-author-tooltip__job-title_1-0" class="comp mntl-author-tooltip__job-title mntl-text-block">Math and Physics Expert</span> <ul id="mntl-author-tooltip__education_1-0" class="comp mntl-author-tooltip__education mntl-block"><li id="mntl-author-tooltip__education-item_1-0" class="comp mntl-author-tooltip__education-item mntl-text-block">M.S., Mathematics Education, Indiana University</li> <li id="mntl-author-tooltip__education-item_2-0" class="comp mntl-author-tooltip__education-item mntl-text-block">B.A., Physics, Wabash College</li></ul> <div class="mntl-author-tooltip__bio"> Andrew Zimmerman Jones is a science writer, educator, and researcher. He is the co-author of "String Theory for Dummies." </div> </div> <div class="mntl-author-tooltip__bottom"> <span class="mntl-author-tooltip__learn-more-text">Learn about our</span> <a href="/about-us-4779650#toc-editorial-guidelines" rel="nocaes" class="mntl-author-tooltip__learn-more-link" >Editorial Process</a> </div> </div></div> </div> <div class="mntl-attribution__item-date">Updated on February 12, 2020</div></div> </div></div> </div><div class="loc article-content"><div id="article-content_1-0" class="comp article-content mntl-block"><div id="mntl-sc-page_1-0" class="comp mntl-sc-page mntl-block structured-content expert-content" data-sc-sticky-offset="85" data-sc-ad-label-height="24" data-sc-ad-track-spacing="100" data-sc-min-track-height="250" data-sc-max-track-height="600" data-sc-breakpoint="50em" data-sc-load-immediate="3" data-sc-content-positions="[1, 1050, 1250, 1550, 1950, 2350, 2750, 3150]" data-bind-scroll-on-start="true"><p id="mntl-sc-block_1-0" class="comp mntl-sc-block mntl-sc-block-html"> Speed is the distance traveled per unit of time. It is how fast an object is moving. Speed is the scalar quantity that is the magnitude of the velocity vector. It doesn't have a direction. Higher speed means an object is moving faster. Lower speed means it is moving slower. If it isn't moving at all, it has zero speed. </p> <div id="mntl-sc-block_2-0" class="comp mntl-sc-block mntl-sc-block-adslot mntl-block"></div> <p id="mntl-sc-block_3-0" class="comp mntl-sc-block mntl-sc-block-html"> The most common way to calculate the constant velocity of an object moving in a straight line is the formula: </p> <div id="mntl-sc-block_4-0" class="comp mntl-sc-block mntl-sc-block-adslot mntl-block"></div> <p id="mntl-sc-block_5-0" class="comp mntl-sc-block mntl-sc-block-html"> <em>r</em> = <em>d</em> / <em>t</em> </p> <div id="mntl-sc-block_6-0" class="comp mntl-sc-block mntl-sc-block-adslot mntl-block"></div> <p id="mntl-sc-block_7-0" class="comp mntl-sc-block mntl-sc-block-html"> where </p> <div id="mntl-sc-block_8-0" class="comp mntl-sc-block mntl-sc-block-adslot mntl-block"></div> <ul id="mntl-sc-block_9-0" class="comp mntl-sc-block mntl-sc-block-html"> <li><em>r</em> is the rate, or speed (sometimes denoted as <em>v</em>, for <a class="CMY_Link CMY_Valid" href="https://www.thoughtco.com/velocity-definition-in-physics-2699021" data-component="link" data-source="inlineLink" data-type="internalLink" data-ordinal="1">velocity</a>)</li> <li><em>d</em> is the distance moved</li> <li><em>t</em> is the time it takes to complete the movement</li> </ul> <div id="mntl-sc-block_10-0" class="comp mntl-sc-block mntl-sc-block-adslot mntl-block"></div> <p id="mntl-sc-block_11-0" class="comp mntl-sc-block mntl-sc-block-html"> This equation gives the average speed of an object over an interval of time. The object may have been going faster or slower at different points during the time interval, but we see here its average speed. </p> <div id="mntl-sc-block_12-0" class="comp mntl-sc-block mntl-sc-block-adslot mntl-block"></div> <p id="mntl-sc-block_13-0" class="comp mntl-sc-block mntl-sc-block-html"> The instantaneous speed is the limit of the average speed as the time interval approaches zero. When you look at a speedometer in a car, you are seeing the instantaneous speed. While you may have been going 60 miles per hour for a moment, your average rate of speed for ten minutes might be far more or far less. </p> <div id="mntl-sc-block_14-0" class="comp mntl-sc-block mntl-sc-block-adslot mntl-block"></div> <span class="heading-toc" id="toc-units-for-speed"></span><h2 id="mntl-sc-block_15-0" class="comp mntl-sc-block reference-sc-block-heading mntl-sc-block-heading"> <span class="mntl-sc-block-heading__text"> Units for Speed </span> </h2> <p id="mntl-sc-block_16-0" class="comp mntl-sc-block mntl-sc-block-html"> The SI units for speed are m/s (meters per second). In everyday usage, kilometers per hour or miles per hour are the common units of speed. At sea, knots (or nautical miles) per hour is a common speed. </p> <div id="mntl-sc-block_17-0" class="comp mntl-sc-block mntl-sc-block-adslot mntl-block"></div> <span class="heading-toc" id="toc-conversions-for-unit-of-speed"></span><h2 id="mntl-sc-block_18-0" class="comp mntl-sc-block reference-sc-block-heading mntl-sc-block-heading"> <span class="mntl-sc-block-heading__text"> Conversions for Unit of Speed </span> </h2> <figure id="mntl-sc-block_19-0" class="comp mntl-sc-block reference-sc-block-table mntl-sc-block-universal-table"> <div class="mntl-sc-block-universal-table__table-wrapper"> <table class="mntl-sc-block-universal-table__table"> <colgroup style="" span="1"></colgroup> <colgroup style="" span="1"></colgroup> <colgroup style="" span="1"></colgroup> <colgroup style="" span="1"></colgroup> <colgroup style="" span="1"></colgroup> <thead> <tr> <th></th> <th>km/h</th> <th>mph</th> <th>knot</th> <th>ft/s</th> </tr> </thead> <tbody data-check="0"> <tr> <th>1 m/s =</th> <td>3.6</td> <td>2.236936</td> <td>1.943844</td> <td>3.280840</td> </tr> </tbody> </table> </figure> <div id="mntl-sc-block_20-0" class="comp mntl-sc-block mntl-sc-block-adslot mntl-block"></div> <span class="heading-toc" id="toc-speed-vs-velocity"></span><h2 id="mntl-sc-block_21-0" class="comp mntl-sc-block reference-sc-block-heading mntl-sc-block-heading"> <span class="mntl-sc-block-heading__text"> Speed vs Velocity </span> </h2> <p id="mntl-sc-block_22-0" class="comp mntl-sc-block mntl-sc-block-html"> Speed is a scalar quantity, it does not account for direction, while velocity is a <a class="CMY_Link CMY_Valid" href="https://www.thoughtco.com/introduction-to-vector-mathematics-2699043" data-component="link" data-source="inlineLink" data-type="internalLink" data-ordinal="1">vector</a> quantity which is aware of direction. If ran across the room and then returned to your original position, you would have a speed — the distance divided by the time. But your velocity would be zero since your position didn't change between the beginning and the end of the interval. There was no displacement seen at the end of the time period. You would have an instantaneous velocity if it were taken at a point where you had moved from your original position. If you go two steps forward and one step back, your <a class="CMY_Link CMY_Valid" href="https://www.thoughtco.com/speed-of-light-3072257" data-component="link" data-source="inlineLink" data-type="internalLink" data-ordinal="2">speed</a> isn't affected, but your velocity would be. </p> <div id="mntl-sc-block_23-0" class="comp mntl-sc-block mntl-sc-block-adslot mntl-block"></div> <span class="heading-toc" id="toc-rotational-speed-and-tangential-speed"></span><h2 id="mntl-sc-block_24-0" class="comp mntl-sc-block reference-sc-block-heading mntl-sc-block-heading"> <span class="mntl-sc-block-heading__text"> Rotational Speed and Tangential Speed </span> </h2> <p id="mntl-sc-block_25-0" class="comp mntl-sc-block mntl-sc-block-html"> Rotational speed, or angular speed, is the number of revolutions over a unit of time for an object traveling in a circular path. Revolutions per minute (rpm) is a common unit. But how far from the axis an object is its radial distance as it revolves determines its tangential speed, which is the linear speed of an object on a circular path? </p> <div id="mntl-sc-block_26-0" class="comp mntl-sc-block mntl-sc-block-adslot mntl-block"></div> <p id="mntl-sc-block_27-0" class="comp mntl-sc-block mntl-sc-block-html"> At one rpm, a point that is at the edge of a record disk is covering more distance in a second than a point closer to the center. At the center, the tangential speed is zero. Your tangential speed is proportional to the radial distance times the rate of rotation. </p> <div id="mntl-sc-block_28-0" class="comp mntl-sc-block mntl-sc-block-adslot mntl-block"></div> <p id="mntl-sc-block_29-0" class="comp mntl-sc-block mntl-sc-block-html"> Tangential speed = radial distance x rotational speed. </p></div> <div id="sources-and-citation_1-0" class="comp sources-and-citation mntl-block"><div id="citation-widget_1-0" class="comp citation-widget js-citation-widget" data-tracking-container="true"> <div class="citation-widget__container js-container"> <button class="citation-widget__button js-button"> <span class="citation-widget__cite-label">Cite this Article </span> <svg class="icon icon-cite citation-widget__icon-cite" > <use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#icon-cite" href="#icon-cite"></use> </svg> </button> <div class="citation-widget__window js-window"> <svg class="icon icon-close citation-widget__icon-close js-icon-close" > <use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#icon-close" href="#icon-close"></use> </svg> <div class="citation-widget__heading">Format</div> <a href="#" class="citation-widget__format-link citation-widget__format-link--active js-format-link">mla</a> <a href="#" class="citation-widget__format-link js-format-link">apa</a> <a href="#" class="citation-widget__format-link js-format-link">chicago</a> <div class="citation-widget__heading">Your Citation</div> <div class="citation-widget__content js-content"> <span class="citation-widget__citation citation-widget__citation--active js-active" data-citation-format="mla">Jones, Andrew Zimmerman. "What Speed Actually Means in Physics." ThoughtCo, Apr. 5, 2023, thoughtco.com/speed-2699009.</span> <span class="citation-widget__citation" data-citation-format="apa">Jones, Andrew Zimmerman. (2023, April 5). What Speed Actually Means in Physics. Retrieved from https://www.thoughtco.com/speed-2699009</span> <span class="citation-widget__citation" data-citation-format="chicago">Jones, Andrew Zimmerman. "What Speed Actually Means in Physics." 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