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Today’s Science
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Newton’s 2nd Law: Day 1
Today’s Science
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Newton’s 2nd Law: Day 2
Let’s revisit Newton’s 1st
Law
•
An object in motion stays in
motion with the same speed
and direction unless acted
upon by an unbalanced force
Newton's 1st Law
Simulation
“A force to be reckoned with” Lab
Page 44
As the car moves down the
ramp, is the car accelerating or
moving at a constant speed?
As the car moves down
the ramp are the forces
balanced or unbalanced?
What forces are acting on
the car?
•
Force of gravity x mass =
weight
•
Force of friction
What forces are acting on
the car?
•
The forces are unbalanced
•
The car accelerates as the car
moves down the ramp
Why does the distance
decrease as the mass
increases?
Let’s look at weight…
•
Weight = mass x F(gravity)
•
Weight = (1 washer) x (mass
of car) x F(gravity)
•
Weight = 3 x (1 washer) x
(mass of car) x F(gravity)
•
Weight = 5 x (1 washer) x
(mass of car) x F(gravity)
As we increase weight, we
increase the net force acting
downward… the forces become
less and less unbalanced
As we decrease the mass,
the car moves further and
faster (increase acceleration)
Therefore: mass, net
force, and acceleration
are related
Newton’s 2nd Law
Page 45
Newton’s 2nd Law
•
Acceleration of an object depends on the
object’s mass and the net force acting on the
object
•
Net force = mass x acceleration
•
Assuming the same net force is applied, an
object with a smaller mass will move farther than
an object with a larger mass
Unbalanced Forces…
•
Change an object’s velocity
(speed and direction)
Objects speeding up…
•
If the net force acting on a
moving object is in the
direction that the object is
moving, the object will speed
up
•
Net force in same direction =
acceleration
Objects slowing down…
•
When the direction of the net
force on an object is opposite
the direction of motion, the
object slows down
•
Opposing net force =
deceleration
Acceleration
Simulation
Solving Newton’s 2nd Law
Equation Practice: Page 45
Practice #1
•
A soccer ball was kicked. It had a mass of .42kg
and accelerated at 25 m/s. What was the force?
*kg m/s2 = 1 N
Practice #1: Answer
*kg m/s2 = 1 N
Practice #2
•
A force of 20 N acts upon a 5 kg block.
Calculate the acceleration of the object.
Practice #2 Answer
Practice #3
•
An object with a mass of 300 kg is observed to
accelerate at the rate of 4 m/s2. Calculate the
total force required.
Practice #3 Answer
Practice #4: Pre-AP
Practice #4: Pre-AP Answer
Fnorm = 80 N; m = 8.16 kg; Fnet = 40 N, right; a = 4.9 m/s/s,
right
Since there is no vertical acceleration, normal force = gravity
force.
The mass can be found using the equation Fgrav = m • g.
The Fnet is the vector sum of all the forces: 80 N, up plus 80 N,
down equals 0 N. And 50 N, right plus 10 N, left = 40 N, right.
Finally, a = Fnet / m = (40 N) / (8.16 kg) = 4.9 m/s/s.
Practice
Get out your plickers
2 Types of Circular
Motion
Centripetal Force
•
Caused by inertia
•
A force that acts perpendicular
to the direction of motion,
toward the center of the curve
•
“Center seeking”
•
Ex: Swinging a ball on a string
•
•
Ball’s path is curved
because of string pulls ball
inward
Ex: Satellites, moon
Centrifugal Force
•
Caused by inertia
•
Acts outward
•
“Center fleeing”
Newton's 2nd Law:
Explained
Science of the NFL
Today’s Science
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Newton’s 2nd Law: Day 3
Today’s Science
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Newton’s 2nd Law: Day 4