Download Newton`s 2nd Law PPT - Kawameeh Middle School

The acceleration of an object is equal to the
net force exerted on the object divided by
the object’s mass.
Force = Mass x Acceleration
Acceleration = Force
Mass
The acceleration due to gravity on earth =
9.8 m/s2
If you want to find…
Acceleration (a)
Net Force (F)
Mass (m)
And you know…
Net Force (F) and
mass (m)
Acceleration (a)
and mass (m)
Net Force (F) and
acceleration (a)
Then the formula you
would use is…

Identify the information you are given
◦ Look at the units
◦ Unit for Force – Newton (N)
 Remember: Weight is a force due to gravity
 If the problem asks you to solve for weight you need to
identify the acceleration due to gravity for your given
location.
◦ Unit for Acceleration – m/s2
◦ Unit for Mass – Kg or g

Use the appropriate formula

A man has a mass of 66kg on Earth. What is
his weight?

Johnny hits the baseball with 100N of force.
The baseball has a mass of 14.2kg. Identify
the acceleration of the baseball.

A girl on roller skates with a mass of 55kg
accelerates at a rate of 2m/s2. What is her
force?

Richie went fishing with his dad. He felt a
bite on his line and started reeling the fish in
with a force of 201N. The fishing line was
moving at an acceleration of 22m/s2. What
was the mass of the fish that he reeled in?

Balanced Force
The force exerted
by the HAND is
EQUAL to THE FORCE OF
GRAVITY

Unbalanced Force
The force exerted
by gravity is GREATER
than air resistance.

Unbalanced forces cause objects to
ACCELERATE
1. Increase Speed
2. Decrease Speed
3. Change Direction
Part I: Acceleration Depends on Mass
Acceleration decreases as its mass increases
Acceleration increases as mass decreases
Acceleration and mass are inversely related
Example: You are pushing a shopping cart at the
grocery store. At the beginning of your shopping trip,
you exert a small force on the cart to accelerate it.
(smaller mass = greater acceleration)
Exert the same amount of force when the cart is full and the
cart will not accelerate as much. (greater mass = smaller
acceleration)
http://www2.hawaii.edu/~kobatake/secondlaw4.html
Part II: Acceleration Depends on Force
Acceleration
increases as the force on it increases
Acceleration decreases
as the force on it decreases
Acceleration and force are directly related
Example: When pushing the full shopping cart, if
you push harder (greater force), the cart will move
faster.
If you push the full shopping cart with less
force, the cart will move slower.
**The acceleration is always in the same direction as the force applied.
The shopping cart moved forward because the push was in a forward
direction

We know that objects
with different masses
accelerate to the
ground at the same rate.

However, because of
the 2nd Law we know
that they don’t hit the
ground with the same
force.
F = ma
F = ma
98 N = 10 kg x 9.8 m/s/s 9.8 N = 1 kg x 9.8 m/s/s
Newton’s second law explains why objects fall to Earth
with the same acceleration (9.8 m/s)
Less mass
More mass
Less Gravitational force
More Gravitational force
Less inertia = easier to
move
More inertia = harder to
move
Type of
Relationship
Constant
Force
Mass
Acceleration
Mass
Increases
Acceleration
Decreases
________
Mass
Decreases
___________
Force
Increases
Acceleration
Increases
Acceleration
Increases
________
Force
Decreases
____________
Force
Increases
Acceleration
Decreases
Mass
Increases
___________
Force
Decreases
____________
Mass
Decreases
Inverse
Direct
Direct




Any motion in which an object is moving
along a curved path.
For example: A rider on a merry-go-round
moves in a circle. This type of motion is
called Circular motion
If you are in circular motion, your direction of
motion is constantly changing
This means you are constantly accelerating



A force that causes an object to move in a
circular path
If you are constantly accelerating there must
be a force acting on you at all times
The force exerted is the centripetal force and
always points to the center of the circle.


All CIRCULAR MOTION requires a CENTRIPETAL FORCE
Because the force acts toward the CENTER
of the circular path, the acceleration must
also be toward the CENTER