1. Chapter 2: Lesson 3

2. Newton’s 2nd Law of Motion
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 =
Mass x Acceleration
Force
Mass
9.8 m/s2

3. Three Forms of Newton’s 2nd Law
If you want to find…
And you know…
Then the formula you would use is…
Acceleration (a)
Net Force (F)
Mass (m)
Net Force (F) and mass (m)
Acceleration (a) and mass (m)
Net Force (F) and acceleration (a)

4. Units for solving for Newton’s 2nd Law
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
Newton (N)
Weight
gravity
m/s2
Kg or g

5. Practice Problem
A man has a mass of 66kg on Earth. What is his weight?

6. Practice Problem
Johnny hits the baseball with 100N of force. The baseball has a mass of 14.2kg. Identify the acceleration of the baseball.

7. Practice Problem
A girl on roller skates with a mass of 55kg accelerates at a rate of 2m/s2. What is her force?

8. 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?

10. An object at REST Balanced Force The force exerted by the is to
Unbalanced Force The force exerted by gravity is than air resistance.
HAND
GREATER
EQUAL
THE FORCE OF
GRAVITY

11. An object in MOTION Unbalanced forces cause objects to ACCELERATE
Increase Speed
Decrease Speed
Change Direction

12. Acceleration and Mass when Force remains constant.
Acceleration as its mass
decreases
increases
Acceleration as mass
increases
decreases
Example: You are pushing a shopping cart at the grocery store. You want to push with a constant force the entire time.
Without groceries you have a ________________ mass, therefore you accelerate at a _________________ rate.
When you add groceries you ________________ mass and therefore acceleration ____________________.
Acceleration and mass are
inversely related

13. Acceleration and Force when Mass remains constant.
increases
Acceleration as the force on it
increases
Acceleration as the force on it
decreases
decreases
Example: If you finish your grocery shopping at the store your mass in your cart remains constant, however you want to speed up (accelerate) to get to the checkout. In order to increase my acceleration I must ________________ the amount of force applied to the cart.
Acceleration and force are
directly related
**The acceleration is always in the as the force applied. The shopping cart moved forward because the push was in a forward direction
same direction

14. 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
at the same rate.
force.
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

15. 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

16. Constant Type of Relationship
Force
Mass Increases
Acceleration ________
Mass ___________
Acceleration Increases
Mass
Force Increases
Force ____________
Acceleration Decreases
Acceleration
Mass Decreases
Decreases
Inverse
Decreases
Increases
Direct
Decreases
Increases
Direct
Decreases

17. Newton’s Laws can be applied to objects moving
in circular motion.

18. Circular Motion
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
changing
accelerating

19. Centripetal Force
The inward force on a spinning object that stops it from going in a straight line.

20. 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

21. Answer the following with your partner.
Use the diagram to answer each question.
What force keeps the ball moving in a circle?
What is producing this force?
Why is the ball accelerating?
In which direction is it accelerating?
If the ball broke away from the string at the position shown, would it move away on line A, B, or C?
What causes it to take this path?
After breaking away from the string, what is the main force that would be acting on the ball?