1. 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?

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

3. 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

4. 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!

5. 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

6. 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

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

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

9. 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

10. 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

11. 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

12. 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

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

14. 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!