Download Air Resistance Force

NEWTON’S
LAWS O’
MOTION
FORCE
A push or a pull
The Measurement of Force
 m
1 Newton  1kg1 2 
 s 
• 1 Newton is the amount of force
required to give a 1 kg mass an
acceleration of 1 m/s2
• Must have a direction!!!
(yup, it is a vector)
FOUR
FUNDAMENTAL
FORCES
GRAVITATIONAL
FORCE
• An attractive force
between two bodies
• The weakest of all forces
ELECTROMAGNETIC
FORCE
• Charged particles at rest exert
electric forces on each other
• Charged particles in motion
exert magnetic forces on each
other
STRONG NUCLEAR
FORCE
• Holds particles of the
nucleus together
• The strongest of all
forces
WEAK FORCE
• Form of an
electromagnetic force
•Happens when some
nuclei radioactively
decay
7 common forces:
•Applied Force (Fapp)
•Gravity Force (Fgrav )
•Normal Force (Fnorm )
•Friction Force (Ffrict )
•Air Resistance Force (Fair )
•Tension Force (Ftens )
•Spring Force (Fspring )
Weight of an object
is the force of
gravity on object
(Fgrav) = (mass)*(g)
Mass must be in kg and g
2
must be in m/s
NEWTON’S
FIRST
LAW
Newton’s First Law
An object at rest will stay at rest
and an object in motion will stay
in motion with the same speed
and in the same direction, unless
acted upon by unbalanced forces
Possibilities of Newton’s
st
1
Newton’s First Law
Also known as
“The Law of Inertia”
WEARING YOUR
SEATBELT IS THE LAW…
…THE LAW OF INERTIA!
Objects at rest tend to stay at
rest, objects in motion tent to
stay in motion, unless acted
on by an unbalanced force
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INERTIA
the tendency of an
object to resist
changes in motion
The more mass an
object has, the more
inertia it has.
Mass measures the
amount of inertia
BALANCED AND
UNBALANCED
FORCES
BALANCED FORCES
(no motion / velocity / acceleration)
So when all forces are balanced…
UNBALANCED FORCES
(motion / velocity / acceleration)
Imagine a tug of war between two unmatched teams….
One team pulls with a force of 300N to left
…and the other team pulls to right with a force of 600N
One team pulls with a force of 300N to left
+
…and the other team pulls to right with a force of 600N
=
The net force is 300N to the right
When forces are unbalanced:
They don’t completely cancel each
other out and there is a net force.
 there is an acceleration in the
direction of the NET FORCE
NET FORCES
the vector sum of
all forces acting
on an object
Practice with
free-body
diagrams
Practice Finding the Net Force
NEWTON’S
SECOND
LAW
Newton’s Second Law
The acceleration of an object
is directly proportional to the
net force on it and inversely
proportional to the object’s
mass
a = Fnet/m
or
Fnet = ma
Acceleration under
nd
Newton’s 2
• An object will only accelerate if
an unbalanced net force is
acting on it!
• The direction of acceleration is
the direction of the net force
Newton’s Second Law
Algebraic Relationships
nd
of Newton’s 2
•If you double the net force, you
double the acceleration
(if mass is held constant)
•If you double the mass, you halve
the acceleration
(if force is constant)
Newton’s Second Law Applied
(here gravity = 10m/s2)
AIR RESISTANCE
AND TERMINAL
VELOCITY
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True or False
•
•
•
•
•
1. The elephant encounters a smaller force of air
resistance than the feather and therefore falls
faster.
2. The elephant has a greater acceleration of
gravity than the feather and therefore falls faster.
3. Both elephant and feather have the same force
of gravity, yet the acceleration of gravity is
greatest for the elephant.
4. Both elephant and feather have the same force
of gravity, yet the feather experiences a greater air
resistance.
5. Each object experiences the same amount of
air resistance, yet the elephant experiences the
greatest force of gravity.
Air Resistance
TRUE OR FALSE
•
•
•
•
•
•
6. Each object experiences the same amount of
air resistance, yet the feather experiences the
greatest force of gravity.
7. The feather weighs more than the elephant,
and therefore will not accelerate as rapidly as the
elephant.
8. Both elephant and feather weigh the same
amount, yet the greater mass of the feather leads
to a smaller acceleration.
9. The elephant experiences less air resistance
than the feather and thus reaches a larger
terminal velocity.
10.The feather experiences more air resistance
than the elephant and thus reaches a smaller
terminal velocity.
11.The elephant and the feather encounter the
same amount of air resistance, yet the elephant
has a greater terminal velocity.
Air Resistance
• Falling objects initially accelerate
(gain speed) because there is no
force big enough to balance the
downward force of gravity.
• As an object gains speed, it
encounters an increasing
amount of upward air resistance
force.
• objects will continue to
accelerate (gain speed) until the
air resistance force increases to
a large enough value to balance
the downward force of gravity.
TERMINAL VELOCITY
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NEWTON’S
THIRD
LAW
Newton’s Third Law
For every action force,
there is an equal (in
magnitude) and
opposite (in direction)
reaction force
How would the following be
examples of Newton’s 3rd Law?
•A fish swimming through the
water
•A bird flying through the air
•A horse pulling a cart
Identify 6 pairs of action-reaction
forces in the following picture