Animator provides an environment for the student to see real-time animations of physical (and non-physical) situations. Students view these animations and make time, position, velocity, acceleration, and force measurements in order to answer questions about the motion of objects that appear in the Physlet. Because of its versatility, Animator is probably the most robust and widely used Physlet currently available. It has been used to create problems ranging in content from kinematics to particle physics to help students to visualize physical situations.