| Values
for Other Objects
source:
University Textbook
Coefficient of Friction
| Materials |
u static |
u kinetic |
| steel on steel |
0.74 |
0.57 |
| aluminum on steel |
0.61 |
0.47 |
| copper on steel |
0.53 |
0.36 |
| rubber on concrete |
1.0 |
0.8 |
| lubricated metal on metal |
0.15 |
0.06 |
| ice on ice |
0.1 |
0.03 |
| teflon on teflon |
0.04 |
0.04 |
| synovial joint of humans |
0.01 |
0.003 |
Notice
on the table how static friction is greater than the kinetic friction.
When an object moves there is kinetic friction, and this value is ower
than the static friction in which an object is not moving.
For
"teflon on teflon", the values for static and kinetic friction are both
0.04. My guess is that static friction friction is greater than the kinetic
friction at a thousandth decimal place of a mu.
We
can always assume that static friction is greater than the actual kinetic
friction.
The
value of synovial joints in humans is about 0.003 mu.
This
is no surprise if you think carefully: it should have the lowest value
possible so that the friction doesn't deteriorate the cartilage (promoting
arthritis at a young age).
Teflon
on teflon (coating on skis) is low as well. Also, ice on ice is low too.
Note
that steel on steel is 0.57, whereas it is 0.06 when lubricated.
Further,
another reason for the synovial joints to be smoothly sliding is that globules
of synovial fluid are readily available to lubricate the joints. |
