| Force Vector: Use this tool to give body elements constant external forces during Run mode. To attach the force vector, click on the target body, then drag out the vector in the direction and to the length you desire. The force vector appears as a thin black line. The thick black line you often see is actually the net (total) force vector, which you can turn off in the background properties. You can later change the length and direction of the force vector by resizing it, or by setting the strength (magnitude, in N) and direction (degrees) in the vector's Properties Box. You can attach multiple force vectors to one body. You may place up to 20 force vectors. In the Properties Box, you can also set the label the force vector (default is F) and show (or not show) the vector's label, length (i.e., magnitude or strength), and direction (default is to show only the label). Placing a force vector disables the acceleration vector tool. Special Forces: All force vectors, inlcuding those for gravitational, elastic, friction, and normal forces (and net forces), are objects with the same properties. For special forces and net forces, you can change their labels and their show properties (though for gravity, you must first enable label). The strength and direction properties are disabled. Except for gravity, these forces are calculated during Run mode by the simulator, so changing their strength and direction (after enabling the properties) has no effect. However, if you wanted to create a setup with horizontal gravity, you could!