| Body Element/Object: The body element is the basic object upon which all the forces, speeds and devices in the Interactions & Motion simulator operate. You may place as many of these objects as you wish anywhere in the simulation window. With the Select tool, you can move and resize body elements. A body element's text label is a Text Box that can be edited or deleted independently of the body element, and has its own Properties Box. In addition, you can attach body elements to launchers. You can impose push forces, pull forces, thruster forces, and speeds upon body elements. If you impose a central thrusting force on a body, no other forces will act upon a body--not even gravity. Bodies are constrained to move along either the horizontal or vertical directions, but not both. Hence, if you a horizontal speed, you cannot apply a vertical force to the object. The only exception is when a gravitation source is present and the body is constrained to move on a surface. Graph tools can plot any body element's position, speed, or the net force acting on it. If you first select a body element, you can place an energy changes bar graph for that body that will track both changes in different types of energy and work done on the body. In a body's Properties Box, you can change its color (default is cyan) and give the body a name. You can also change the body's mass (default is 5 kg). You may hide or show body name (recall the that body name or label is a Text Box). In addition, you can choose to paste an image to represent the body in place of the default filled square used. The image must first be placed on the CIPS Java Clipboard by the snapshot tool or from the Image Palette. This property allows you to replace the filled square with pictures of cars, boats, aliens, rockets, lions, horses--whatever image may fit your instructional needs. Surfaces. When a gravitation source is present, you can choose to have the object (body) move on a horizontal surface. When you choose this option, the body can only move along a horizontal surface. The body experiences a normal force in the +Y direction that exactly cancels the gravitational force and any other vertical forces acting on the object. If vertical forces (excluding the normal force) would cause the object to move upward, the simulation stops and the simulator flashes an error message. The property surface property allows you to determine how rough the surface is. The surface can be frictionless (no friction), smooth, rough, or very rough. The frictional force is proportional to the normal force.