Download Newton`s Second Law 2 PPT

Objective
• SWBAT use Newton’s first and second laws to
identify and explain changes in the velocity of
objects.
The man who follows the crowd will usually get no
further than the crowd. The man who walks alone is
likely to find himself in places no one has ever been.
—Albert Einstein.
Balanced Forces  No acceleration
Newton’s First Law
Check For Understanding
• Which statement below correctly summarizes
Newton’s first law?
A. When a force acts on an object, the object accelerates
in the direction of the force.
B. When the net force acting on an object is zero, the
object stays at rest, or if the object is already moving,
it continues to move in a straight line with a constant
speed.
C. When unbalanced forces act on an object, the object
will not move.
D. When balanced forces act on an object, the object
will accelerate.
Supertankers illustrate the
principal of inertia; their
engines are cut off a mile
or more before the tanker
enters port and it still
coasts right on in.
You are driving in a car with no seat belt on. You see a
family of ducks and slam on your brakes to avoid hitting
them. Since you are not wearing your seat belt, you fly
out of the car (remain in motion) until you hit the
ground (an unbalanced force).
AHH!
Ouch
In motion…
At rest…
Unbalanced Forces  Acceleration
Forces are either balanced, or unbalanced
When forces are
equal, no acceleration
occurs.
Forces are either balanced, or unbalanced
But when they are
unbalanced, that’s
when objects
accelerate
Forces are either balanced, or unbalanced
But when they are
unbalanced, that’s
when objects
accelerate
Forces are either balanced, or unbalanced
But when they are
unbalanced, that’s
when objects
accelerate
Forces are either balanced, or unbalanced
But when they are
unbalanced, that’s
when objects
accelerate
Newton’s Second Law
Check For Understanding
• If an object is accelerating, which statement
below is true?
A. The object is being acted on by balanced forces.
B. The object is being acted on by unbalanced
forces.
C. The object is not being acted on by any forces.
D. You do not know whether the forces are
balanced or unbalanced.
If F = ma…
• The more force you put in, the more
acceleration an object will have.
If I throw the ball really hard
If I throw the ball softly
(F = 10 N), then the ball will
(F = 1 N), then the ball will
go really fast, (A = 20 m/s2)
go slowly, (A = 2 m/s2)
Newton’s Second Law
The more mass an object has, the more force
you have to put in to move it.
It would be hard to move an elephant
(more force), because he is so heavy
(more mass).
It would be easy to move a baby duck
(less force), because he is so light
(less mass).
Newton’s Second Law
• If you exert an equal force on two objects, the
lighter object (the one with less mass) will
accelerate faster.
F = 10 N
Check For Understanding
• What property of a stalled car determines
how much effort is required to move it?
A. Height
B. Mass
C. Volume
D. Length
Check For Understanding
• Elrick pushes a textbook and a file cabinet. The
textbook has a mass of 10 kg. The file cabinet has
a mass of 300 kg. He pushes them both with a
force of 50 N. Which box will accelerate at a
faster rate?
A. The textbook
B. The file cabinet
C. They will accelerate at the same speed
D. Neither will accelerate – they will move with
constant velocity.
Check For Understanding
• Tanesha is mad at Maegan and Jahina, but she is
REALLY mad at Maegan. She pushes Maegan with
a force of 40 N, and she pushes Jahina with a
force of just 5 N. If Jahina and Maegan have the
same mass, who will accelerate faster after being
pushed?
A. Jahina
B. Maegan
C. They will accelerate at the same speed
D. Neither will accelerate – they will move with
constant velocity.