Model Description
Investigate slipping and tipping for Coulomb Friction. This demonstration should take 5-10 minutes.
Engineering Principle
These training aids provide a vehicle to discover the need to consideration three possibilities when investigating friction problems: 1) Nothing happens 2) Slipping occurs, 3) Tipping occurs.
What You Need
| Item | Quantity | Description/Clarification |
|---|---|---|
| Ramp | 1 | A board or tilted desk could also work. $10 |
| Block | 1 | Two sides with sandpaper, two sides without. $10; 15 minutes |
| Chair / Cord / Student | 1 | Used for the “Executioner’s Chair” |
How It’s Done
Before Class: Prepare the box with sand paper.
In Class: Block with sandpaper: With the appropriate degree of inclination, the smooth side of the block will slip (lengthwise) and the rough side will not (with no applied force). Putting the block on edge, the smooth side of the block will slip and the rough side will tip with an applied force.
Executioner’s Chair: Students always enjoy impending doom. With a chair and a cord, one can quickly bring out the teaching points of why it matters where the cord is attached to the chair, how the force of friction increases as the applied force increases, why it matters if tape is put on the floor, and the fact that tipping or slipping could occur. Intuitively, the students know the answer to all these questions, now one can discover the statics to support it.
Where to attach? Bottom — Ok.
He slides!
What if the cord is attached to the top? Still sliding!
Now there is tape on the floor. He tips!