Science Buddies: "Ask an Expert"

Hello, I have a few questions about Physics for my Science fair project.
First, my project is: Create a program that simulates physics. As a continuation from my last year's project, I want to add in the factors of friction with a ball rolling down an inclined slope.
My first question is, will friction affect a ball rolling down an inclined slope if the ball had different surface areas? And if so, which factor of friction?
Next, with a ball rolling down the inclined slope, will surface friction affect the speed of the ball rolling down?
Also, when similar balls are rolled down differently inclined slopes, is friction a factor in this?
Thank you in advance

Hi HansDaBest,

Welcome to the Ask an Expert forums!

In the standard model of friction, the force of friction does not depend on surface area. A ball rolling down a slope will be affected, to some extent, by friction. The magnitude of the effect depends on the coefficient of kinetic friction between the two materials, so if different balls have different friction coefficients, then the forces of friction acting on them will be different. The difference will be proportional to the ratio of the coefficients, all other factors equal. The slope of the hill is also important. Different slopes results in different normal forces between the ball and the ramp. This is because frictional forces depend on the normal component of the net force on the ball. The online physics textbook called "Hyperphysics" has some really helpful pages about friction, which I've linked to below. Check them out to get a better feel for how friction works. Post back with the things you find confusing, and we'll help you with those questions.

http://hyperphysics.phy-astr.gsu.edu/hbase/frict.html
http://hyperphysics.phy-astr.gsu.edu/hbase/frict3.html
http://hyperphysics.phy-astr.gsu.edu/hbase/frict2.html