1. Do Now:
1. How does a Newton’s Cradle represent all 3 of Newton’s Laws of motion? Explain for each law!

2. EPISODE II : The Vectors Strike Back
The EVIL Vector Empire has once again
reared its ugly head...
The students in
Mr. Rao’s physics
classes stage their
attempt to defeat
the empire...
PHYSICS
WARS

3. Free Body Diagram Vector Diagram Shows ALL FORCES on an object
Must be properly LABELLED. FN Fg

4. IF Net Force ≠ 0 FN FA Fg The object is ACCELERATING or DECELERATING
ΣFx = FA = Fnet FN
Students must FA m Fg
Frictionless

5. 4 Steps for Newton’s Law Problem
Draw a Free Body Diagram
Sum up vertical and horizontal forces SEPERATELY.
Write Newton’s Second Law for vertical and horizontal!
Solve for Unknown
*** A 1.0 kg hokey puck is smacked with a 50 N force to the right on frictionless ice. What is the puck’s acceleration?

6. Example
A 1 kg block is pushed to the right with 20N force, while being pulled to the left with 15N force.
Draw a Free Body Diagram
What is the blocks acceleration?
15 N
20 N

7. Post Activity- A 50. -newton box is moving on the table below
Post Activity- A 50.-newton box is moving on the table below. Calculate the acceleration of the box. Determine the normal force and draw a FBD.
35.-N
10.-N
50.N

8. Envelope Activity
Draw the free body diagram for each scenario described.

9. A 10 kg block is suspended in the air at rest, while being pulled to the right and left by two forces.
What do we know about the two forces?
A 50 kg ice skater is pushed onto frictionless ice with a force of 10 N. What is her acceleration?
A 5 kg crate is pushed down on with a force of 10 N. What is the normal force?

10. Pulling on an Upward Angle
The applied force (FA)
can be broken into
COMPONENTS
FAY = FA sin θ
FAY = 50N
ΣFY = 0
Fg + FN + FAY = 0
FN = 48.1 N
How will this affect
the Normal Force?
Which force will
accelerate the object?
FAX = FA cos θ
FAX = 86.6 N
If frictionless,
Fnet = FAX FN
FA = 100N
10kg
FAY
30˚
ACCELERATION
depends only
on FAX !
FAX
The NORMAL
force supplied
by the surface is
REDUCED! Fg
Fg = N

11. Example
A man pulls a 40 kilogram crate across a smooth, frictionless floor with a force of 20 N that is 45˚ above horizontal.
Explain what would happen to the acceleration if the box were
pulled at a greater angle. How about at a smaller angle?
Calculate the net force on the sled.
Fnet = FA cos θ
Fnet = (20 N)(cos 45°)
Fnet = N
At a greater angle, the horizontal component of the force would
be smaller, making Fnet and acceleration decrease.
A smaller angle would increase Fnet and acceleration.
Calculate the crate’s acceleration.
a = Fnet / m
a = (14.14 N) / (40 kg)
a = 0.35 m/s2

12. White Board Competition
A girl pushes a 30 kilogram lawnmower with a force of 15 Newtons at an angle of 60˚ below horizontal.
Assuming there is no friction, calculate the
acceleration of the lawnmower.
Fnet = FA cos θ
Fnet = (15 N)(cos 60°)
Fnet = 7.5 N
a = Fnet / m
a = (7.5 N) / (30 kg)
a = 0.25 m/s2
How can she maximize her acceleration?
Push at an angle closer to 0° (horizontal)

13. Exit Card What are the 4 steps for solving a Newton’s law problem?
What does it mean for a force to be applied at an angle?