Lecture 8: Friction
recorded by: Massachusetts Institute of Technology, MIT
published: Oct. 10, 2008, recorded: September 1999, views: 7751
released under terms of: Creative Commons Attribution Non-Commercial Share Alike (CC-BY-NC-SA)
Download mit801f99_lewin_lec08_01.m4v (Video - generic video source 103.5 MB)
Download mit801f99_lewin_lec08_01.rm (Video - generic video source 104.8 MB)
Download mit801f99_lewin_lec08_01.flv (Video 104.5 MB)
Download mit801f99_lewin_lec08_01.wmv (Video 423.9 MB)
Report a problem or upload filesIf you have found a problem with this lecture or would like to send us extra material, articles, exercises, etc., please use our ticket system to describe your request and upload the data.
Enter your e-mail into the 'Cc' field, and we will keep you updated with your request's status.
1. Normal and Frictional Forces:
Starting with a block at rest on a horizontal surface, Professor Lewin describes the normal force, the maximum frictional force that must be overcome to budge the block, and the coefficient of static friction. Once the block is budged and begins to slide, you encounter a smaller coefficient of kinetic friction.
2. Measurements of the Coefficient of Static Friction:
Consider a block at rest on an inclined plane, and increase the tilt until the block just starts to slide. By measuring this tilt angle you can calculate the coefficient of static friction. The friction coefficient only depends on the materials in contact; it is independent of the mass of a sliding object and independent of its surface area (this is rather non-intuitive).
3. Another Way to Measure Friction:
The system consists of a block on an inclined plane. The block is counterbalanced by a second mass connected to the block with a massless string and a near massless, frictionless, pulley. The direction of the frictional force depends on whether the block on the incline wants to move uphill or downhill or stay at rest. By increasing the second mass until the block on the incline budges uphill, you can measure the coefficient of static friction.
4. Ways to Reduce Friction - Fleas are Good for Something!
Scenarios for reducing friction are presented including hydroplanes and air tracks. Even a flea can move a very heavy book if the friction is near zero (as demonstrated).
Link this pageWould you like to put a link to this lecture on your homepage?
Go ahead! Copy the HTML snippet !