Download Document

Newton’s Third Law + Review
• Newton’s Third Law Examples
• Review
• Quiz
Outline
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
The Math
FA on B = - FB on A
Fapp
A
B
Example: Two blocks are pushed with an applied force.
Determine the acceleration of the blocs and the
action/reaction forces FAB and FBA.
Fapp
A
B
Review
Walk–Back/Forth
x [m]
Draw the v-t and a-t graphs for the x-t graph
t [s]
QQ29: 2-D
Components
Exercise
Determine the numerical values of the x and y components of each
vector:
y
120
y

A
5
x
x
45
10

B
Ax = __________
Ay = __________
Bx = __________
By = __________
What would A+B look like ?

Fg
We divide the contact
force into two
components”

FA

f

n

- normal force : n is perpendicular to the surfaces
in contact

- friction : f is parallel to the surface
Demo
Ex: Two blocks are connected over a frictionless pulley.
What is the acceleration of the system given no friction.
m1=2kg
m2=1kg
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.
θ
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.
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!