Introduction

This project aims to create an interactive kinetic punching bag using oobleck—a non-Newtonian fluid that solidifies under force. The system uses an Archimedes screw to elevate oobleck from a reservoir to a waterfall-style faucet, allowing the fluid to cascade down in intermittent blobs or a steady stream. When punched with sufficient force, the oobleck behaves like a solid, allowing for a clean impact. If the punch is too soft, the user’s hand passes through, encouraging stronger strikes. This combines physics education, stress relief, and physical training into a single, mesmerizing device.

URS
Physics
Free Body Diagram
Design
BOM
Electronics
Code
Modeling
Fabrication
Guides
Notes
Contact

URS

User Requirement Specifications

Constraints	Approach	Achieved
Safe to touch	Use food-grade cornstarch and water with optional preservative
Clean rebound	Oobleck solidifies on impact, rebounds punch without splatter
Visual appeal	Waterfall faucet + LED lighting
Adjustable speed	Variable-speed Archimedes screw motor
Compact design	Self-contained trough and screw unit
Durable system	Use non-stick, corrosion-resistant materials
Power	Plug-in wall adapter or 12V battery with inverter
Interactive	Optional strike sensor to measure force

Physics

Non-Newtonian fluid behavior: Oobleck exhibits shear-thickening properties.
At low speeds, it behaves like a liquid; at high impact, it becomes a solid.
Impact force must exceed a critical shear threshold for the fluid to resist deformation.

Free Body Diagram

Forces: Downward gravity, upward Archimedes torque, lateral strike forces.
Resistance increases with impact speed due to fluid phase behavior.

Design

Base: Trough containing oobleck
Archimedes screw: Lifts oobleck to height of waterfall faucet
Waterfall faucet: Allows oobleck to fall back into trough
Front panel: Impact area with optional LED strips
Enclosure: Transparent acrylic with sealed joints
Sensors (optional): Accelerometers or force sensors to measure strike quality

BOM

Item	Quantity	Notes
Cornstarch	Bulk	For oobleck
Water	Varies	Ratio ~2:1 with cornstarch
Acrylic sheets	4-6	Transparent casing
Archimedes screw	1	3D printed or metal/plastic helix
DC motor with controller	1	Variable speed
LED strips	2-4	Optional lighting
Power supply	1	Wall plug or 12V battery
Tubing (optional)	Varies	For redirection / overflow control
Force sensors	Optional	For gamification or feedback

Electronics

Motor driver connected to DC motor and speed dial (potentiometer)
LEDs controlled via microcontroller or simple switch
Sensors (optional): Accelerometer or force sensor readouts
Microcontroller (optional): ESP32 or Arduino for automation and display

Code

Optional – if force sensors or LED patterns are used.

// Example pseudocode
if (strikeDetected) {
    measureForce();
    displayLEDpattern();
    logScore();
}

Modeling

3D CAD model of enclosure with screw channel, trough, and punch face
Fluid simulation for oobleck movement optional but useful
Test in Blender/Unity/SimScale for visual validation

Fabrication

Cut acrylic panels
Assemble enclosure and seal joints
Install Archimedes screw and motor
Mount waterfall faucet
Wire up motor and LEDs
Fill with oobleck and calibrate flow rate

Guides

Oobleck Mix: 2 parts cornstarch to 1 part water
Cleaning: Flush system weekly; avoid letting oobleck dry in pipes
Safety: Use gloves when mixing preservatives; ensure enclosure is leakproof

Notes

Oobleck will settle over time—design should allow for stirring or agitation
May require periodic refills depending on evaporation
Consider adding glycerin to reduce drying time without overly thinning

Oobleck non Newtonian fluid punching machine