[tatianabassatne]

I am doing my physic coursework and have to explain why the greater the mass, the greater the frictional force,that the more uneven the surface the more frictional force and finally the greater the surface area the greater the friction. Please help it is for my coursework.

[cdedmundson]

the equation to find the frictional force is F(friction)=μN where μ is the coefficient of friction and N is the normal force.
1.) the more mass you have the greater force downward due to gravity, and the normal force is the reactionary force acting against your applied force (i.e. the ground pushing up on you, the wall pushing against you when you push against it) in other words your normal force is always perpendicular to your surface, and since gravity acts downward on a flat surface your normal force is equal to your gravitational force, N=F(gravity)=mass*gravitational acceleration (9.8)
2.) the more uneven the surface area means a higher μ or coefficient of friction. μ increases with the level of unevenness so a μ of 0 means friction is non-existent and a μ of 1 means an object will not move. (μ cannot exceed 1 because that would cause you to push on a stationary object and it move opposite of the force you applied)
3.) it is pretty much common sense that the more surface area present the more the object is affected, I don't know a formal definition of why this is but think of it like trying to move two pieces of velcro parallel to each other when you have 1 square inch versus 1 square foot.