Relationship Between Force and Friction
OK. Here is another simple challenge: Get a meterstick. Place one finger near the 15 cm mark and the other finger near the 65 cm mark. Move both fingers together at approximately the same velocity, so they meet together at the 40 cm mark. Is that asking too much?
What You Need
- Place the meterstick horizontally and hold with an outstretched finger from each hand.
- Place your fingers near the 15 and 65 meter markings of a meterstick (Figure 45-1).
- Move both fingers at roughly the same velocity, so they meet at the 40 meter mark.
This does sound simple enough but this is just about impossible for most people to do. You will find you can only move the finger furthest from the center (the one starting at the 15 centimeter mark) until both fingers are the same distance from the center. Then, they meet close to the middle (the 50 cm mark). See Figure 45-2.
Why It Works
A lot of physics is actually in this little investigation. The force is greater on the finger furthest from the center (because there is greater torque trying to rotate the meterstick in that direction). The greater the force, the greater the force of friction. This results in one finger being able to move much more easily than the other.
Other Things to Try
Try this with different starting finger positions. You may also need to convince any skeptics that one side of the meterstick does not have more friction than the other.
The further a weight is from a pivot point, the greater the force it exerts. Greater force between the surfaces in contact results in greater friction.
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