I looked at that, but unfortunately there's about as much misinformation as worthwhile comments there. And I couldn't find any that match what I've always taken to be the explanation: that there's an energy threshold to be overcome.tolove said:
haruspex said:I looked at that, but unfortunately there's about as much misinformation as worthwhile comments there. And I couldn't find any that match what I've always taken to be the explanation: that there's an energy threshold to be overcome.
Imagine e.g. that the two surfaces are made of materials which, if completely flat, would have no friction at all. But instead of being flat, each consists of parallel ripples. At rest, the two sets of ripples interlock. A small amount of energy needs to be invested in lifting the block over the ripples, but that energy is then available to get it over the next ripple, and so on.
It needn't be physical ripples - it could be some electrostatic bonding, but the concept is the same.
So I did a quick search and found this http://www.khanacademy.org/science/...on-on-static-and-kinetic-friction-comparisons
Only that it jibes with what I thought up myself.tolove said:Do you have an idea of how accurate his presentation is?
The kinetic friction coefficient (fk) is typically less than or equal to the static friction coefficient (fs) because static friction is a force that opposes motion, while kinetic friction is a force that acts on objects already in motion. This means that it takes less force to keep an object in motion (kinetic friction) than it does to overcome the initial resistance to motion (static friction).
The value of the kinetic and static friction coefficients depend on several factors, including the types of materials in contact, the roughness of their surfaces, and the amount of force applied. These coefficients are experimentally determined and can vary depending on the specific conditions.
No, the kinetic friction coefficient can never be greater than the static friction coefficient. This is because static friction is the maximum amount of force that can be applied to an object before it starts moving, while kinetic friction is the amount of force required to maintain motion. Therefore, by definition, the kinetic friction coefficient is always less than or equal to the static friction coefficient.
The value of the kinetic and static friction coefficients directly affect the motion of an object. A higher value of static friction coefficient means it will require more force to get an object to start moving, while a higher value of kinetic friction coefficient means it will take more force to keep the object in motion. These coefficients also determine the amount of heat energy produced due to friction.
Yes, the value of the kinetic friction coefficient can change depending on various factors such as the surface roughness, temperature, and the presence of lubricants. For example, a smoother surface will result in a lower kinetic friction coefficient, while a rougher surface will result in a higher coefficient. Additionally, the presence of a lubricant can significantly reduce the value of the kinetic friction coefficient.