Download i. what is a force?

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The Nature of
FORCES
I. WHAT IS A FORCE?
a. A force is ___________________
a push or a pull
b. A force is described by:
its strength
1.___________________
the direction
2.___________________
c. The strength of a force is measured in a unit
called ____________
NEWTON [SI unit = ______
N ]
“You exert about 1 newton of force when you lift a small lemon”
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I. WHAT IS A FORCE?
d. Often, more than a single force acts on an object
at a time. The combination of all forces acting
on an object is called the ____________.
net force
e. When forces act on an object from the same
“add” the forces together
direction, _____________________________.
1N
6N
5N
NET FORCE
f. The object will always move in the direction
____________________.
of the larger force
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I. WHAT IS A FORCE?:
g. When forces act on an object from
subtract the forces
“opposite” directions ____________________.
5N
10 N
5N
h. If the opposing forces are of equal strength
________________________________________
there is “no net force” and no change in
the
object’s motion (forces cancel out)
_______________________________________
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II. TIPPING THE BALANCE
1. Unbalanced forces cause an
object to:
start moving
a. _________________
stop moving
b._________________
c._________________
change direction
2. Unbalanced forces acting on an
object results in a net
___________
force
and cause a change in
______________________.
the object’s motion
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II. TIPPING THE BALANCE
3. When forces are exerted on an object, the
object’s motion does not always change.
4. Balanced forces:
are equal forces acting on one object in
a. _________________________________
opposite directions
_________________________________
do not change the object’s motion
b. _________________________________
5. Write 3 examples of balanced forces:
a cup resting on a table
1. _________________________________
a truck moving at constant speed
2. _________________________________
arm wrestling or “tug of war”
3. _________________________________
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II. TIPPING THE BALANCE
Practice:
Two tug boats are TOWING a submarine into port. Tugboat A exerts a
force of 2000 newtons on the submarine. Tugboat B exerts a force of
4000 newtons in the opposite direction.
Tugboat A
2000 N
•
Tugboat B
4000 N
Draw arrows showing the individual and combined forces of the
tugboats.
B)
1. What is the combined force on the barge? 2000 N (tugboat
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2. Is this is a balanced or unbalanced force? unbalanced
III. THE FORCE OF GRAVITY
a. The force of GRAVITY
1. Gravity is the force that
pulls objects to Earth
________________________
a. Two factors that affect gravity are:
mass of object
1. ______________________
distance
2. ______________________
between all objects
2. The force of gravity acts _______________________
increases
3. If mass increases, the force of gravity ____________
4. If distance increases, the force of gravity
Decreases
____________
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IV. WEIGHT
1. WEIGHT is
A
measure of the gravitational force
____________________________________
exerted
on the an object.
___________________________________
2. ________varies
with the strength of the
WEIGHT
gravitational force, but ______
MASS does not.
WEIGHT = mass x gravity or [W=mg]
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V. OTHER FORCES
1. Elastic force:
Force exerted by stretching
___________________________
___________________________
certain materials
2. Buoyancy:
Upward force by H20 on an
___________________________
___________________________
object
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V. OTHER FORCES
3. Magnetism:
___________________________
Objects exert an attractive
or repulsive forces on each
___________________________
other
___________________________
4. Static Electric:
amount of electric charge on
___________________________
___________________________
the surface of an object
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*** Let’s Review ***
$ What is the difference between
mass and weight?
$ Explain the difference between a
balanced and unbalanced force?
10 N = ?
$ 5N
$ Will an object move if the net force
acting on an object are unbalanced?
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VI. FIGHTING FRICTION
a. Friction:
The force that 2 surfaces exert on each other when
____________________________________________
____________________________________________
they move against each other
b. The strength of friction depends on two factors:
how hard surfaces push together
1. ___________________________________
the types of surfaces involved
2. ___________________________________
c. Friction acts in a direction
Opposite to the direction of object’s motion
___________________________________________
It must overcome friction
d. For an object to move __________________________
e. Without friction
____________________________________________
A moving object will not stop until it strikes another
____________________________________________
object
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VII. TYPES OF FRICTION
a. STATIC friction:
acts on objects that are
___________________________
not moving
___________________________
b. SLIDING friction:
friction between 2 solid
___________________________
___________________________
surfaces sliding past one
___________________________
another
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VII. TYPES OF FRICTION
c. ROLLING friction:
the resistance that occurs
1.____________________________
when a round object such as a
___________________________
ball or tire rolls on a flat surface
___________________________
is easier to overcome than
2.____________________________
__________________________
sliding friction
d. FLUID friction:
friction between a solid object
1._____________________________
and a fluid
____________________
2. 3 types of fluid friction include
• ____________
Water (H20)
• ____________
oil
air
• ____________
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VII. TYPES OF FRICTION
PRACTICE:
1. To actually move an object, you must use a force that
is greater than the force of _________
STATIC friction.
FLUID friction.
2. Air resistance is a type of ________
Name 3 examples of each type of friction below:
SLIDING
______________
______________
______________
ROLLING
______________
______________
______________
FLUID
_______________
_______________
_______________
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*** Let’s Review ***
$ Which kind of friction keeps your
shoes from slipping on the floor?
$
[T/F] To move an object, you must use a force
that is less than the force of static friction?
$
What would happen if there was no
friction?
$
How would you describe the texture of a
surface that produces a lot of friction?
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VIII. NEWTON’S LAWS OF MOTION
a. Newton’s FIRST law: (INERTIA)
An object at rest will stay at rest
a. __________________________
An object in motion will stay in
b. __________________________
motion unless acted upon by an
__________________________
force
__________________________
b. INERTIA
a. _____________________________
The tendency of an object to
_____________________________
resist a change in motion
b. The greater the _____of
an
mass
object the greater the inertia.
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VIII. NEWTON’S LAWS OF MOTION
c. Newton’s SECOND law: (ACCELERATION)
a. Is the rate in which an object speeds
UP or DOWN
b. acceleration depends on the
object’s______
mass and on the ______
force
acting on the object.
m/s2
c. Units for acceleration = ______
Net force
Acceleration
=
-----------------PRACTICE
mass
A speedboat pulls a 55 kg water
1. Fnet = acceleration x mass
skier. The force causes the skier
2) (55 kg)
2.
Fnet
=
(2.0
m/s
to accelerate at 2.0 m/s2. Calculate 3. Fnet = 110 kg * m/s2
the net force that causes this
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acceleration.
Fnet = 110 N
VIII: NEWTON’S LAWS OF MOTION
c. Newton’s THIRD law:
equal
opposite
1. For every action there is an ______but
_________
reaction.
Normal
Force
Force of
Gravity
WILL NOT
MOVE
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*** Let’s Review ***
$ Explain Newton’s First Law of Motion
$
[T/F] The greater the mass the greater the
inertia
$
What is the formula for acceleration?
Name the forces acting on the
$ Jeep?
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