1. Newton’s Third Law + Review
Newton’s Third Law Examples
Review
Quiz
Outline

2. Action  Reaction Newton’s 3rd Law
NIII definition
Newton’s 3rd Law
“If object A exerts a force on object B, then object B exerts a force equal in magnitude and opposite in direction on A”
Action  Reaction

3. The Math
FA on B = - FB on A B
Fapp A

4. Example: Two blocks are pushed with an applied force
Example: Two blocks are pushed with an applied force. Determine the acceleration of the blocs and the action/reaction forces FAB and FBA. B A
Fapp

5. Review

6. Draw the v-t and a-t graphs for the x-t graph
Walk–Back/Forth
Draw the v-t and a-t graphs for the x-t graph
x [m]
t [s]

7. Exercise Ax = __________ Bx = __________ Ay = __________
QQ29: 2-D Components
Exercise
Determine the numerical values of the x and y components of each vector: y y
120 5 x x
45 10
Ax = __________
Ay = __________
Bx = __________
By = __________
What would A+B look like ?

8. We divide the contact force into two components”
normal force : is perpendicular to the surfaces in contact
friction : is parallel to the surface

9. Demo
Ex: Two blocks are connected over a frictionless pulley. What is the acceleration of the system given no friction.
m1=2kg
m2=1kg

10. Demo
Ex: A block is moving down a ramp that makes an angle θ with the horizontal. What is the acceleration of the system given that there is friction. m1 θ

11. QQ38: Inequality
Example:
A horizontal force of 150 N is applied to a 50 kg box on a level floor. The coefficient of static friction between the box and the floor is 0.5. What magnitude of the frictional force on the box.

12. What to review look over all the lecture notes
write down ‘key concepts’ that you think are important
be able to use x-t, v-t, a-t graphs
understand normal forces (ramps, level)
be able to find acceleration for simple systems
free body diagrams
look over projectile motion
don’t worry about any long derivations we did in class!