Download Newton`s 2nd Law

Essential Questions
• Who discovered the Three
Laws of Motion?
• What is Newton’s Second
Law & how does it apply to
motion?
Newton’s First Law
“An object at rest tends to stay at rest
and an object in motion tends to stay
in motion unless acted upon by an
unbalanced force.”
More Laws of Motion
• Newton’s First Law of Motion states that if
you kick a ball, the ball will move.
• Newton’s Second Law of Motion says that
when a force acts on an object, the object
accelerates.
– If you kick the ball harder, it will move faster.
– It also tells you that a heavy ball is harder to
move than a lighter ball.
Newton’s Second Law
Force equals mass times acceleration.
F = ma
Acceleration: a measurement of how quickly an
object is changing speed. (Acceleration occurs when an object speeds up, slows
down, or changes its direction of motion... ANY CHANGE IN MOTION IS ACCELERATION)
Mass: the amount of matter in an object
NEWTON’S SECOND LAW
The more force that is
applied, the more the object
will accelerate.
NEWTON’S SECOND LAW
The object will accelerate in
the direction of the force.
Newton’s Second Law of Motion
• A long row of shopping carts takes more
force to move than one empty cart
requires.
Takes more force to move
NEWTON’S SECOND LAW
The more mass an object has,
the harder it is to accelerate.
The less mass an object has,
the easier it is to accelerate.
This truck takes more to
accelerate because it has
a lot of mass.
Let’s Look at it This Way..
• A car will stop suddenly if the driver slams
on the brakes.
• However, if the driver applies the brakes
gently, the car gradually slows down.
What does F =MA mean?
Force is directly proportional to mass and acceleration.
Imagine a ball of a certain mass moving at a certain
acceleration. This ball has a certain force.
Now imagine we make the ball twice as big (double the
mass) but keep the acceleration constant. F = ma says
that this new ball has twice the force of the old ball.
Now imagine the original ball moving at twice the
original acceleration. F = ma says that the ball will
again have twice the force of the ball at the original
acceleration.
What does F = ma say?
F = ma basically means that the force of an object
comes from its mass and its acceleration.
Something very massive (high mass)
that’s changing speed very slowly (low
acceleration), like a glacier, can still
have great force.
Something very small (low mass) that’s
changing speed very quickly (high
acceleration), like a baseball, can still
have a great force. Something very
small changing speed very slowly will
have a very weak force.
Let’s Review
• What is the effect of a car’s
acceleration if six people
ride in the car instead of
one?
Let’s Review
• Acceleration is produced by _________.
– A.) masses
– B.) forces
– C.) velocity
– D.) pressure
Let’s Review
• True or False
If…
Force = mass x acceleration
Then…
Acceleration = force / mass
(net force)
Acceleration…
• Remember our question from the
beginning of class?
If someone told you that a car was
accelerating, what would that mean to
you?
• What would you say now?
How is slowing down
acceleration?
• Acceleration in the same direction as
velocity speeds up an object.
• Acceleration directed opposite of velocity
slows down an object.
• Acceleration on an object with zero
velocity makes the object START to move
in the direction of the acceleration.
Newton’s 2nd Law Centers
Station 1:
 Eraser Racers
Station 2:
 Speed Racers
Station 3:
 Weighty Situation
Station 4:
 Speeding Train
Station 5:
 Explaining Newton’s Laws
Station 6:
 Taking notes