KITE Lets Learners Feel Forces in Digital Physics Simulations
Elizabeth Childs, a Stanford PhD candidate, presents KITE as a way to make forces in physics simulations physically perceptible. The hand-moved robot travels freely until a learner encounters a virtual object or force, then pushes back with corresponding force or torque. Childs argues that this combination of tangible movement and responsive feedback lets students explore relationships such as lift, molecular attraction and friction through physical interaction rather than screen representations alone.
KITE makes simulated forces part of the learner’s movement
Elizabeth Childs describes KITE as a robot that can be moved by hand but also pushes back, simulating forces, torques and impacts. It lets students explore physics through physical interaction: rather than only seeing a force represented on a screen, they can feel its direction and response as they move through a simulation.
In an electrostatic-field demonstration, a learner moves KITE as if they were a proton. The display shows KITE being pushed away from a positive charge and pulled toward a negative one. Those simulated pushes and pulls become tangible as the learner navigates the field.
KITE must combine free movement with resistance. When it is not interacting with a force, it can move freely like a mouse; when it reaches a virtual object, it must generate the corresponding force feedback. The robot’s movement remains unimpeded until a simulated interaction calls for it to push back. That transition is central to the design: the same device has to feel freely movable in one moment and deliver a directed physical response in the next.
Responsive tracking keeps force feedback in step
Childs says the team uses gearless motors and a custom motor driver to command forces and torques. To deliver forces in any direction without turning, KITE uses a three-wheeled circular design. The prototype also has a handle, a camera for tracking and a Raspberry Pi as its onboard computer. The mobility requirement is mechanical as well as computational: KITE needs to move in any direction while keeping its orientation, so the force it applies can align with the interaction on screen.
The camera points upward while KITE sits on a monitor. Ceiling LEDs provide reference points: the camera compares their positions in its image to estimate KITE’s location. Childs says this method gave the team accurate positioning, but camera updates were not frequent enough for precise force rendering. The team therefore combines camera tracking with motor feedback: motor readings estimate KITE’s position between camera frames, and each new frame corrects that estimate.
That faster position estimate matters when a user pushes KITE into a virtual wall. To make contact feel realistic, the robot must push back with an equal and opposite force. As KITE penetrates the wall, the system smoothly reverses the wheel’s torque. The wall example shows why accuracy alone is not enough: force feedback also needs to respond quickly as the user moves into a simulated object.
Different physics relationships become different physical sensations
In aeronautics, students can feel the force from airflow and experience how the shape and angle of an airfoil provide lift. The display shows KITE pushing down when the foil points nose down and pushing up when it points nose up. The direction of the physical response changes with the foil’s angle, making lift something the learner encounters through movement rather than only observing in the airflow display.
In a molecular-physics example, learners can physically pull hydrogen bonds apart and feel KITE oppose bond breaking. The robot also pulls toward nearby molecules. Childs describes the interaction as a way to feel how electronegativity drives atomic attraction and forms ions.
Tidal forces make gravity’s variation with distance tangible. Students feel a stronger pull near the moon and a weaker one farther away. Childs connects this difference to water being pulled away from Earth on the near side and left behind on the far side.
Other demonstrations show how physical responses change with an arrangement or a kind of motion. Students can feel the force of springs in single, series and parallel configurations, and experience how stiffness changes between those arrangements. They can also compare Coulomb friction, represented as a constant opposing force, with viscous friction: a small force when moving slowly and a stronger force when moving quickly. The comparison makes the distinction experiential: the resistance of one surface stays constant, while the fluid-friction response varies with the speed of movement.
Across these examples, a learner moves through a digital representation while KITE supplies a physical response corresponding to the simulated force or interaction. Childs’s closing description is concise:
Whatever the scenario, KITE makes digital experiences feel real.