Friction and Gravity: Can Physics Be Defined by Math?

[betteragnostc]

The formula of friction force is

Ff = μN

can also be defined as

Ff = μ.m.g

One of my friend say that mathematically, that equation tell us that when there is a gravity force, Ff can't be zero assuming that there is no zero μ

Is that true? While on static condition I will say that even when there's a gravity force, the friction force is zero. But he said then if it is in static condition, then the formula would be

Fmax = μ.m.g

which mean when there is a gravity force, Fmax can't be zero.

Can physics really defined just by formula mathematically?

 

[tiny-tim]

The formula of friction force is

Ff = μN

No, that only applies to dynamic friction and when the bodies are about to become dynamic (ie Fstatic = Fmax).

In the static case, Ff < µN

… But he said then if it is in static condition, then the formula would be

Fmax = μ.m.g

which mean when there is a gravity force, Fmax can't be zero.

Yes, Fmax can't be zero, but Ff can be zero.

 

[betteragnostc]

Yes, Fmax can't be zero, but Ff can be zero.

Is that true that the only condition Ff can be zero on gravity influence, is when the mass become completely static?

 

[tiny-tim]

I don't really understand what you're asking.

If the mass is moving, then the friction force is always µN.

 

[Alvasin]

Which us easier to pull or push?Is there any impact of friction?If so how the mass will effect to that?