What are four factors that can affect the amount of friction between two objects

As the Force of friction is equal to µ by using the Law of Action Reaction; as the force normal is the conterforce of gravity

µ
µ

Therefore, by looking at the equation we can infer that

The force of friction is directly proportional to the mass, gravitational constant, and the co-efficent of friction

Because the gravitational constant is dependant on gravitation, a planet's mass and radius also affect the force of friction

But DO NOTE:
That the co-effecient of friction is only applicable between two rubbing surfaces and unaffected by gravitational constants. 

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