Chapter 4c

Forces and Friction

Demos to Prepare:

For Theories of Friction:
Rough surfaces-- bricks.
Smooth surfaces--  glass plates.
Lubrication— wet the plates.
Rolling--  ball bearings.
Starting  vs. sliding friction.
Starting is higher.
Eraser on board.
Train startup.
Skidding.
Sled & weight on incline.
Spring  balance dragging a mass.
The Creeper.
Hydroplaning.
Water under tyre at 300kg.
Internal friction--  Bong & Blop.
Vortex generator--  smoke rings
Caterpillar lube job on RR tracks.
Zero friction-- Nails & bolts, motion?
Terminal velocity of marble in caro syrup.

The Great Molasses Disaster of 1919. Viscosity!

Phone Book Friction, Video

Firemen Blast Cat from Tree with the Big Hose.

Terminal velocity saves a cat falling 25 meters, Video:

Terminal velocity of a penny dropped from the Empire State Building. Can it kill anyone? Video:

Terminal velocity of bullets fired up. Can they kill us? Video:

Powerful steam locomotives would frequently spin their wheels when starting up because sliding (spinning) friction is lower than starting friction. Video:

Hydroplaning is the separation of the tires from the road by water when driving too fast. Spindown of car tires occurs because the friction of the bearings is higher than the friction between water and road. Videos:

Anti Lock Brakes! Video:

The Coefficient of Friction is the ratio of the force of friction to the normal force. Normal is at right angles.

Clear the Table Inertia/Friction Video

Low friction air track levitator. A vacuum cleaner blower suspends the disk above the floor. Total upward force equals the pressure times the surface area. Video:

Elevator Crash! Can a person in a freely falling elevator save himself by jumping up just as the elevator hits bottom? Video:

Does it matter when driving a pickup truck if the tail gate is up or down? Video:

Here Endeth Chapter 4c