1. Warm-Up Sept 4, Sept 5, 2013
Describe the actions necessary to move a box from one side of the room to the other.
Where are all the safety equipment in the classroom/lab?

2. Introduction to Forces
January 7, 2014

3. Lesson Objectives
The students will be able to correctly identify contact and field forces in everyday life.
The students will be able to identify the forces acting on an object and correctly diagram them.
The students will safely work to move down the hallway in rolling chairs.

4. What is Force?
Force is any kind of push or pull applied to an object or body.
Are forces only present when we can see the physical contact?
No! Only contact forces require touching to transmit the push or pull
Field forces require no physical contact to transmit their push or pull.
Example:

5. Who is credited with discovering force?

6. ISAAC NEWTON Isaac Newton:
English scientist who was the first person to put into words the behavior of objects in motion
These ideas became his Laws of Motion

7. Newton’s 1st Law
An object will remain constant unless acted on by an outside force
What does this mean?
Objects moving will keep on moving OR
Objects sitting still will stay still…
Unless something comes along to change that

8. Newton’s 1st Law Examples:
The door will remain closed until someone attempts to open it
You will stay in your seat until something happens (like the bell ringing)

9. Force = mass x acceleration
Newton’s 2nd Law
An object’s Force is equal to the object’s mass times its acceleration
Force = mass x acceleration
F = ma

10. Forces Quantity Chart Quantity Symbol in Formula Unit Unit’s Symbol
Newtons N
Net Force
FNET
Mass m
kilogram kg
Acceleration a
meters per second per second
m/s/s or
m/s2

11. F = ma F = (0.2 kg) x (14.2 m/s2) F = 2.84 N Newton’s 2nd Law Example:
A baseball is thrown toward a batter with an acceleration of 14.2 m/s2. If the ball has a mass of 0.2 kg, what force does the ball have when it reaches the batter?
F = ma
F = (0.2 kg) x (14.2 m/s2)
F = 2.84 N

12. Newton’s 3rd Law
For every action there exists an equal and opposing action.
Law of Action/Reaction

13. Newton’s 3rd Law Example:
Can you spot all the examples of Action/Reaction?

14. Newton’s Laws

15. Newton’s Laws

16. Newton’s Laws

17. Forces Activity Draw a diagram of the following situation:
A student sitting in a chair being pushed across the room

18. WHAT IS A FREE-BODY DIAGRAM?
A free-body diagram (FBD) is a drawing of an object and all the forces acting on it. FN Ff FA Fg

19. VECTORS FAQ What is a Vector?
Anything which has both direction and size (magnitude)
Vectors are used in FBD’s to show how much force is acting on an object and in which direction

20. FREE BODY DIAGRAMS What is a free-body diagram? FN Ff FA FD Fg
A picture representation of all the forces acting on an object FN Ff FA FD Fg

21. NET FORCE & VECTORS
The net force (FNET) is found when you add all the vectors in their corresponding directions
Add all the vectors along the x-axis
Add all the vectors along the y-axis
Add all the vectors along the z-axis (but we really don’t get into 3-D vectors)
Find the resultant with the Pythagorean Theorem

22. Net Force & Vectors Example:
A 12 Newton force pushes northward and a 7 Newton force pushes eastward on the same object. What does the resultant vector look like?
What is the magnitude of the resultant vector?

23. FREE-BODY DIAGRAMS Draw a free-body diagram for the following problem:
A 280 N car is driving down the road in an attempt to pass another car. The driver applies a force of 28 N, but there exists a drag force of 14 N. Correctly label all the above forces in a free-body diagram.
280 N
14 N
28 N
280 N

24. Vector Addition

25. Force & Motion Net Force (FNET) is the sum of all forces on an object
What happens when the FNET is not zero?
The object is accelerating. What does this mean?

26. Force & Motion
When the net force (FNET) acting on an object is zero (0), what do you think this means for that object’s motion?

27. Force & Motion
Objects will only change their motion when they experience “unbalanced” forces.
This means when there is more force in one direct than another, an object’s motion will change

28. Force & Motion Net Force (FNET) is the sum of all forces on an object
The object is NOT accelerating. What does this mean?

29. Homework
Please record the following questions and YOUR answers in your Physics Notebook
Research Newton’s Three Laws of Motion and find one example of each in everyday life.