Chapter 2: Lesson 3
Jan 01, 2016
Ch
ap
ter
2:
Lesson
3
The acceleration of an object is equal to the net force exerted on the object divided by
the object’s mass.
Force =
Acceleration =
The acceleration due to gravity on earth =
Newton’s 2nd Law of Motion
9.8 m/s2
Mass x Acceleration
ForceMass
If you want to find…
And you know… Then the formula you would use is…
Acceleration (a)
Net Force (F)
Mass (m)
Three Forms of Newton’s 2nd Law
Net Force (F) and mass (m)
Acceleration (a) and mass (m)
Net Force (F) and acceleration (a)
Identify the information you are given◦ Look at the units◦ Unit for Force –
Remember: is a force due to 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 – ◦ Unit for Mass –
Use the appropriate formula
Units for solving for Newton’s 2nd Law
Newton (N)
m/s2
Kg or g
Weight gravity
A man has a mass of 66kg on Earth. What is his weight?
Practice Problem
Johnny hits the baseball with 100N of force. The baseball has a mass of 14.2kg. Identify the acceleration of the baseball.
Practice Problem
A girl on roller skates with a mass of 55kg accelerates at a rate of 2m/s2. What is her force?
Practice Problem
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?
Practice Problem
An object at REST Balanced Force The force exerted
by the is to
Unbalanced Force The force exerted by gravity is than air resistance.
GREATER HAND
EQUAL THE FORCE OF GRAVITY
Unbalanced forces cause objects to
An object in MOTION
ACCELERATE
1. Increase Speed2. Decrease Speed3. Change Direction
Part I: Acceleration Depends on Mass
Acceleration as its mass
Acceleration as mass
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
decreases increases
increases decreasesAcceleration and mass are inversely related
Part II: Acceleration Depends on ForceAcceleration as the force on it
Acceleration as the force on it
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 as the force applied. The shopping cart moved forward because the push was in a forward direction
increases increases
decreases decreases
Acceleration and force are directly related
same direction
We know that objects with different masses accelerate to the ground
However, because of the 2nd Law we know that they don’t hit the ground with the same
F = ma
98 N = 10 kg x 9.8 m/s/s
F = ma
9.8 N = 1 kg x 9.8 m/s/s
at the same rate.
force.
Newton’s second law explains why objects fall to Earth with the same acceleration (9.8 m/s)
Less mass
Less Gravitational force
Less inertia = easier to move
More mass
More Gravitational force
More inertia = harder to move
ConstantType of
Relationship
Force
Mass Increases
Acceleration ________
Mass ___________
Acceleration Increases
Mass
Force Increases
Acceleration ________
Force ____________
Acceleration Decreases
Acceleration
Force Increases
Mass ___________
Force ____________
Mass Decreases
Decreases
Increases
Increases
Inverse
Direct
Direct
Decreases
Decreases
Decreases
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
If you are in circular motion, your of motion is constantly
This means you are constantly
Circular Motion
direction
Circular motion
accelerating
changing
Centripetal Force 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
The force exerted is the and always points to the center of the circle.
at all times
centripetal force
All requires a
Because the force acts toward the of the circular path, the acceleration must also be toward the
CIRCULAR MOTION CENTRIPETAL FORCE
CENTER
CENTER