1. 270
34 N
13 N
510
2/ 1 cm:2N
1/ 1 cm:5N

2. 1 cm:10 N
42N
1 cm:4 N 10 N
200
460
6.5 cm  26N
4.2 cm  42N
1 cm:3 N
1 cm:8 N
Fx = 0
Fx = 40 N
Fy = 0
Fy = -6 N

4. Newton’s 1st Law of Motion:
If the ____________________ force, Fnet, acting
on an object equals ________, then that object has
____________________ . Its acceleration a = _____ .
It is said to be in __________________ .
net (resultant)
zero
constant velocity
equilibrium
Because forces are ______________ and have
____________ , the x and y _______________ of the
forces often must be added up _______________
when there are forces along different _________.
vectors
direction
components
separately
axes
net Fx
________ = 0
Fnet = 0 really means:
net Fy
________ = 0

5. Ex: A 20-N box at rest on a table being pushed down with a 5 N force.
Free body diagrams:
Ex: A 20-N box on a table
at rest
FN = 20N
20-N
w = FN
"At rest"  __________
w = 20 N
Ex: A 20-N box at rest on a table being pushed
down with a 5 N force.
5-N
FN = 25 N
20-N
5 N
w + push = FN
w = 20 N
"At rest"  _______________
Both of these boxes are in ___________________ .
equilibrium

6. Ex: Same box sliding to the right on a horizontal
frictionless table at a constant velocity 2.0 m/s
v = 2.0 m/s
FN = 20N
20-N
w = 20N
"constant velocity"  __________
w = FN
velocities
Draw only the __________ , not the ____________
forces
Notice:
1/ The free body diagram is the _________ as the
first example. Both are in ___________________ .
2/ No force is ___________ to keep box moving.
The box will continue its motion ________________.
same
equilibrium
needed
forever

7. Ex: The forces acting on a 20-N box are shown at right:
FN = 20N
pull
= 10N
Ff =
10 N
w = 20 N
This box is in ___________________. It is either:
1/ _____________ (constant velocity = _____);
2/ or _____________ at a constant velocity.
equilibrium
at rest
moving
Unless other information is given, it is
_______________ to tell if it is at rest or moving.
impossible

8. Ex. The three forces below are the only ones
acting on an 2.0-kg object. What is the
acceleration of the object?
Add them up:
3.0 N
4.0 N
5.0 N
3.0 N
5.0 N
4.0 N
The net force Fnet = _____ so a must = ____ .
This object could be _______________ or
moving with ____________________________ .
at rest
constant velocity

9. If an object is ____________ or moving with
Restatement of 1st Law:
If an object is ____________ or moving with
_____________________, it is_________________.
Then the net force (Fnet ) acting on it _________ .
at rest
constant velocity
in equilibrium
= 0
Ex: A B-2 bomber flying
at constant velocity:
lift = 1.3 MN
Ff (drag)
= 300 kN
thrust =
300 kN
weight ≈ 1.3 x 106 N
thrust ≈ 75 x 103 N/engine
x 4 engines
w= 1.3 MN

10. The
“air force”

11. Ex. The two forces shown below act on an
object. What third force is needed to produce
equilibrium? F1 F2
First way to solve:
Find resultant force F
The answer is -F: F -F
balances
-F ___________________ the other two forces.

12. Add the two forces using head to tail method.
Second way to solve:
Add the two forces using head to tail method.
Add a force to "bring the total force to zero."
original
head to tail: F1 F2 F1 -F F2
Notice:
Both ways give ________________________
-F is NOT the ________________ of the other
vectors. It is the force that ________________
the other vectors, making Fnet =________. It is
sometimes called the ________________ because it
is what is needed to produce ___________________ .
the same result
resultant
"balances out"
equilibrant
equilibrium

13. Ex. Draw the vector that represents the force
that the beam exerts on point A.
beam
force
wire T A A
beam
building
weight w
The beam force is the ________________ . It must
be added to the other forces so that ___________
equilibrant
Fnet = 0

14. Ex. Increasing angle between 2 wires supporting a picture:5 1 2 1 2
T = ____
in each
wire
Case 1: vertical
wires
10 N
w = 10 N 7
T = ____
in each
wire 1 2 2 1
Case 2: greater
angle
10 N
w = 10 N
Case 3: even
greater
angle
T = ____
in each
wire 10 1 2 2 1
10 N
w = 10 N
increases
As q increases, the tension _______________ .

15. A net force is ________________ to maintain
motion. An object will maintain its motion in
the ________________ of a net force. This idea
was discovered by _____________. An object in
motion tends to ____________________ , and an
object at rest tends to _________________ . The
_______________________ that “makes” this
true is called its ___________ .
not needed
absence
Galileo
stay in motion
stay at rest
property of matter
inertia
Ex. What has more inertia,
a truck or a baseball?
truck
inertia
more __________
more___________
mass
inertia
mass

16. Inertia is the tendency of an object to
_________________________ . More inertia (mass)
means it is __________________ for an object to…
1/ …_____________________ when it is at rest;
2/ … __________ when it is already moving; and,
3/ … ____________________ from a straight path.
In other words, ______________ is why an object
needs __________________
to maintain its motion.
This is why Newton's
_____________ is called
the ________________ .
resist changes in motion
more difficult
start moving
stop
move sideways
inertia
no net force
equilibrium
Law of
Inertia
1st Law
Law of Inertia
Fnet a
= 0
= 0

17. Open your 3-ring binder to the Worksheet Table of Contents.
Record the title of the worksheet:
Newton’s First Law WS