FINDING THE COEFFICIENT OF FRICTIONAlso the well known “piece

of cake”It really is easy.Trust me. Of course you will

need a CALCULATOR!!!!!!

WE NEED A PROBLEM

An engine provides 5000N of force on a 1600 kg car moving at uniform speed. What is the coefficient of friction between the road and the tires?

Time to work an equation

Put it on your sheet.

HERE IT ISFirst uniform tells us there is no acceleration.

So we have:F= 5000 Nm = 1600kgg = 9.8Coefficient = ?

Ff =mg x cofUsing algebra isolate cof

Now we have cof = Ff/m x gIn numbers cof = 5000 / (1600)(9.8)

Do the math in order!!!!!Answer will be .3188…..

Round up .32

SO WE PUT THEM TOGETHER

Static Friction-(Mus) We know what this is.

Kinetic Friction(Muk) We know this.

So how do we work a problem?SIMPLE!!!!

NOW WE GET COMPLICATED

Like so:

• We have a box that has a mass of 50kg.• If it takes 156.8 N of force to move it what

is the static coefficient ?• First convert the mass ( 50 x 9.8) (490N)• Then we divide force needed (156.8) by

force mass (490) 156.8/490 = .326….. Round to

• 0.33

EASY NO? NOW FOR KINETIC FRICTION

Kinetic means moving. You push a 100 kg rock down the

road. ( You are STRONG!!!) If the coefficient of kinetic friction

(Muk) is .25 between the road and rock how much force is needed to keep the rock moving?

First we find Fn for the rock (100kg) ( 9.8 m/s^2) = 980N

NOW we plug in our formula

(Muk) (Fn) = ?(.25) (980N) = 245NSo it takes 245 N of force to keep the rock moving.

Easy!!!!!!!!!!!!

NOW YOU DO IT.

• A car with a mass of 1500 kg needs a force of 2000 N to get it moving. What is the Mus?

• .1360…………. (.14)• Andrea wants to move a 70 kg John. If the Mus is .20 how much force does she need?

• 137.2 N• Simple?????

Last Ones

• 60 kg Joe is moving down the hall, but looks like he wants to stop. If the Muk is .50 how much force must Coach Ahrens apply to keep him moving?

• (60N) (9.8) x .50 = 294 N• 110 kg Colton is headed for the end zone. If Tristain has to apply 460 N of force to help him score what is the Muk?

•460/ (110 x 9.8) = .4267….. Round .43

OH NO

Review tomorrowTEST THURSDAY!!!!!!!!!!!!!!!!