I know that friction is determined by the equation $$F_f = \mu_fF_n ,$$ so technically if the normal force is $0$ then the force of friction will also be zero, but my question here is whether or not it is possible, or even exists, to have the coefficient of friction constant equal to $0$. If it is not possible then why not? And if it is possible, are there any current examples? This can apply to both kinetic and static friction.
[Physics] Is it possible to have a coefficent of friction of zero
forcesfrictionnewtonian-mechanics
Related Solutions
It's so simple because it's only a first order approximation model to how friction actually works.
There are several other models, but to use them you usually need more parameters or other pieces of information about the system (for example, if there are fluid lubricants involved, the pattern of the surface, the materials involved, etc).
The model $F_f = \mu F_N$ is called Coulomb model of friction. It assumes 3 important laws:
1. Amonton's first law of friction
The magnitude of the friction force is independent of the area of contact.
This law dates back to Leonardo da Vinci:
2. Amonton's second law of friction
The magnitude of the friction force is proportional to the magnitude of the normal force.
Here is an example of experimental data showing the dependence of friction with normal force:
The slope gives the friction coefficient: $\mu = F_f/F_N$.
This also dates back to Leonardo da Vinci, who noticed that if the load of an object was doubled, its friction would also be doubled.
3. Coulomb's law of friction
The kinetic friction is independent of the sliding velocity.
This is only somewhat true for small changes in velocity. Some models account for this dependence:
a) Coulomb model (without static friction)
b) Coulomb model + viscosity (without static friction)
c) Coulomb model + viscosity
d) Coulomb model + viscosity + Stribeck effect
Limitations
Here is an example of experimental data showing the dependence of friction with velocity:
Here is an example showing non linearity with respect to the normal force:
The author comments on the graph above:
What’s going on here? Let’s look at the data for the teflon (the blue data). I fit a linear function to the first 4 data points and you can see it is very linear. The slope of this line gives a coefficient of static friction with a value of 0.235. However, as I add more and more mass to the friction box, the normal force keeps increasing but the friction force doesn’t increase as much. The same thing happens for friction box with felt on the bottom.
This shows that the “standard” friction model is just that – a model. Models were meant to be broken.
Here is another simple article about the limitations of the Coulomb model of friction.
The normal reaction force is not necessarily equal to weight. When you jump, you push down on the ground. That pushing force plus your weight result in a normal reaction force larger than your weight, which is why you are propelled off the ground.
For astronauts in a space ship, they can push against a wall to generate the normal force necessary for friction (or traction) to allow them to propel themselves parallel to the wall. They necessarily push themselves away from the wall at the same time, so they would need to use multiple walls to move from one place to another.
If you watch a video of astronauts on the International Space Station, you'll see that every spare section of wall has hand holds to allow for easier movement because of the reduced friction.
Best Answer
Just use superfluid helium under your bloc, and you should get $\mu = 0$. The bloc could be made to inject liquid helium under its own base.