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      <title>About Units and Dimensions</title>
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      <div class="title_topic2" id="xps10_pagetitle">About Units and Dimensions</div>
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      <p class="para_topic"><b class="uiTerm">Dimension</b> is the expression of some unit measuring a physical property or quantity. Although each quantity can be measured by a variety of units (seconds, meters, pounds, etc.), it has only one dimension (time, length, force, etc.). The units and dimension systems used in NX are divided into two categories: Absolute and Gravitational.
      </p>
      <div class="title_division">Absolute Dimension System</div>
      <p class="para_division">The absolute system (dynamical or physical dimension system) is the most widely used in engineering and has the three basic quantities: mass (M), length (L), and time (T). The following is a sample absolute dimensional system table:</p>
      <table cellspacing="3" align="center">
         <tr>
            <th bgcolor="#c0c0c0" colspan="1" rowspan="1" valign="middle">
               <p class="para_th">Physical Quantity</p>
            </th>
            <th bgcolor="#c0c0c0" colspan="1" rowspan="1" valign="middle">
               <p class="para_th">Units of Measure</p>
            </th>
         </tr>
         <tr>
            <td bgcolor="#f4f4f4" colspan="1" rowspan="1" valign="middle">
               <p class="para_td">mass (M)</p>
            </td>
            <td bgcolor="#f4f4f4" colspan="1" rowspan="1" valign="middle">
               <p class="para_td">kilograms, grams, slugs</p>
            </td>
         </tr>
         <tr>
            <td bgcolor="#f4f4f4" colspan="1" rowspan="1" valign="middle">
               <p class="para_td">length (L)</p>
            </td>
            <td bgcolor="#f4f4f4" colspan="1" rowspan="1" valign="middle">
               <p class="para_td">meters, centimeters, feet</p>
            </td>
         </tr>
         <tr>
            <td bgcolor="#f4f4f4" colspan="1" rowspan="1" valign="middle">
               <p class="para_td">time (T)</p>
            </td>
            <td bgcolor="#f4f4f4" colspan="1" rowspan="1" valign="middle">
               <p class="para_td">seconds, seconds, seconds</p>
            </td>
         </tr>
      </table><br><p class="para_division">These quantities can be expressed in metric units (centimeters, grams and seconds) or occasionally in aerospace units (slug, foot, second).</p>
      <div class="title_division">Dimensional Equations of the Absolute System</div>
      <p class="para_division">The following dimensional equations are basic in the absolute system:</p>
      <ul>
         <li>
            <p class="para_item">Area has dimension [L2].</p>
         </li>
         <li>
            <p class="para_item">Volume has dimension [L^3 ].</p>
         </li>
         <li>
            <p class="para_item">Velocity has dimension [L/T].</p>
         </li>
         <li>
            <p class="para_item">Acceleration has dimension [L/T2;].</p>
         </li>
         <li>
            <p class="para_item">Force has dimension [MxL/T2;] (mass x acceleration).</p>
         </li>
         <li>
            <p class="para_item">Moment of inertia for solid body objects has dimension [ML2;].</p>
         </li>
         <li>
            <p class="para_item">Moment of inertia for planar regions has dimension [L4].</p>
         </li>
      </ul>
      <div class="title_division">Unified Units Control</div>
      <p class="para_division">When you navigate to <b class="uiTerm">Analysis</b> &rarr; <b class="uiTerm">Units</b>, you can use any of the five standard unit families.
      </p>
      <ul>
         <li>
            <p class="para_item"><b class="uiTerm">lb. &mdash; in</b>.
            </p>
         </li>
         <li>
            <p class="para_item"><b class="uiTerm">lb. &mdash; ft.</b></p>
         </li>
         <li>
            <p class="para_item"><b class="uiTerm">g &mdash; mm.</b></p>
         </li>
         <li>
            <p class="para_item"><b class="uiTerm">g &mdash; cm.</b></p>
         </li>
         <li>
            <p class="para_item"><b class="uiTerm">kg. &mdash; m.</b></p>
         </li>
      </ul>
      <p class="para_division">If you prefer to customize your own units (different from the five standard units listed above), navigate to <b class="uiTerm">Gateway</b> &rarr; <b class="uiTerm">Analysis</b> &rarr; <b class="uiTerm">Units Manager</b>.
      </p>
      <p class="para_division">With the <b class="uiTerm">Units Manager</b>, you can select a custom unit that better suits your needs, and you can view<b class="uiTerm"> Information</b> and <b class="uiTerm">Analysis</b> results in this unit. Note that in <b class="uiTerm">Gateway</b> &rarr;<b class="uiTerm"> Analysis</b> &rarr; <b class="uiTerm">Units</b>, NX automatically selects <b class="uiTerm">Custom</b> to indicate that you are using your own default custom measurement.
      </p>
      <div class="title_division">Gravitational or Technical Dimension System</div>
      <p class="para_division">The gravitational or technical dimension system has the basic quantities of force (F), length (L), and time (T). This system is used in engineering, along with the absolute system, for computing force, stress, etc. In the unit system of foot-pound-second (f.p.s.), the quantities are measured as:</p>
      <table cellspacing="3" align="center">
         <tr>
            <th bgcolor="#c0c0c0" colspan="1" rowspan="1" valign="middle">
               <p class="para_th">Basic Quantity</p>
            </th>
            <th bgcolor="#c0c0c0" colspan="1" rowspan="1" valign="middle">
               <p class="para_th">Units of Measure</p>
            </th>
         </tr>
         <tr>
            <td bgcolor="#f4f4f4" colspan="1" rowspan="1" valign="middle">
               <p class="para_td">force</p>
            </td>
            <td bgcolor="#f4f4f4" colspan="1" rowspan="1" valign="middle">
               <p class="para_td">lbs</p>
            </td>
         </tr>
         <tr>
            <td bgcolor="#f4f4f4" colspan="1" rowspan="1" valign="middle">
               <p class="para_td">length</p>
            </td>
            <td bgcolor="#f4f4f4" colspan="1" rowspan="1" valign="middle">
               <p class="para_td">ft</p>
            </td>
         </tr>
         <tr>
            <td bgcolor="#f4f4f4" colspan="1" rowspan="1" valign="middle">
               <p class="para_td">time</p>
            </td>
            <td bgcolor="#f4f4f4" colspan="1" rowspan="1" valign="middle">
               <p class="para_td">sec</p>
            </td>
         </tr>
      </table><br><p class="para_division">Because force is mass x acceleration, in this system, mass has dimensions.</p>
      <p align="center"><img align="bottom" src="graphics/ana_infoat58.gif"></p>
      <p class="para_division">This can be expressed as F/(L/T; ), i.e. FxT;/L. So in the f.p.s. system, mass is measured in lbs sec;/ ft. This unit is sometimes called a slug. </p>
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