Science Starter A 10kg child sits on the floor. What is the value of the normal force on the child? A 2kg book has an even larger book sitting on top of it. The normal force of the table on the bottom book is 100 N. What is the mass of the top book?

Today’s Agenda Science Starter Solving Problems w/ Friction Solving Problems w/ Trigonometry In-Class Work Time Summary

Announcements Today is the last day of content for Unit 1: Balanced Forces Tomorrow will be the pre-test (practice test), show up! Unit 1 Test will be Wednesday next week Monday/Tuesday intro to Unit 2

Solving problems with friction Force of Friction (Ff) = coefficient*Normal Force Need to know or solve for the coefficient You will most likely know the mass of the object, use this information!

Solving problems with friction FN= 20N A 2kg box is pushed at a constant speed to the right. The coefficient of friction for the surface is 0.1 Draw the FBD and label all forces with numbers Ff= 0.1*20= 2N FA= 2N FG= 2*10= 20N

Solving problems with friction FN= 5N A .5kg toy car uses a balloon as the power source. The balloon can only push with a force of 1 N. If the car does not move, what is the coefficient of friction in this case? Ff= u *5= 1N FA= 1N u= 1/5= 0.2 FG= .5*10= 5N

Solving problems with friction Remember to balance your forces Remember that friction is (u * Normal Force)

Trigonometry Review √2 2 2 √3 1 1 45o 30o 60o √3 1 1

Trigonometry Review 2 √3 1 Sin (θ) = opposite/hypotenuse Cos (θ) = adjacent/hypotenuse Cos (60) = 1/2 Tan (θ) = opposite/adjacent Tan (60) = √3/1 60o 1

Practice Problem using angles FN=? A 10kg car sits on an incline surface without moving. The incline of the surface is 300 Draw the FBD with numbers FF=? 30o FG=100N

FG=100N FF = Fll = FG* sin (30) FF = 100 * ½ = 50N = FG* cos (30) FN = 100 * √3/2 = 86N FN = FL Cos(30)=FL/FG FL 60o 30o Fll FG=100N Sin (30)=Fll/FG

Problems using angles Setup like any other FBD problem Find the parallel and perpendicular components (vertical and horizontal) Identify which forces are equal Solve for any unknown forces

In-Class Practice Complete problems from FBD worksheet Complete problems from Green Sheet Pick up and complete Friction & Angle problems from front

Summary Pre-test for Unit 1 will be tomorrow Look over your notes and make sure you understand how Newton’s Laws work in the real world Test will be much critical thinking and drawing scenarios in FBD or interaction to understand!