1. Chapter 12 Forces and Motion
Physical Science
Chapter 12
Forces and Motion

2. Forces and Motion What is a Force?
A Force is a Push or Pull Exerted on an Object.
Forces cause Objects to Speed up, Slow down, or Change Direction as they Move.
A Force Exerted on an Object Causes that Object’s Velocity to Change; that is,
All Forces Cause an Acceleration

3. Forces and Motion How can you cause an object to move?
Push on it or pull on it.
Push harder on an object and you have a greater effect on its motion.
If you push the book to the right, the book moves towards right.

4. Forces and Motion Force is a Vector
The Final Force is the Net (Sum) of the Total Forces on an Object
If the Final Force on an Object DOES NOT = 0, the Object Is Accelerating

5. Forces and Motion Combining Forces Forces are Vectors
They May Strengthen Each Other
They May Cancel All or Part of Each Other
They Are Cumulative

6. Units
Forces are measured in units known as
Newtons =N

7. Forces and Motion Example Problem
Two horizontal forces of 225N and 165N are exerted in the same direction on a crate. What is the net force on the crate?

8. Forces and Motion
Solution
225N
165N

9. Forces and Motion
Solution
390N

10. Forces and Motion Example Problem
If the same two horizontal forces of 225N and 165N are exerted in opposite directions on the crate. What is the net force on the crate?

11. Forces and Motion
Solution
225N
165N

12. Forces and Motion
Solution
60N

13. Forces and Motion Types of Forces Friction (Ff or f ) Normal (FN)
Opposes Horizontal Motion
Parallel to Surface
Normal (FN)
Exerted by Surface on the Object
Perpendicular to Surface

14. Forces and Motion Types of Forces Tension (FT) Weight (Fg)
Pull or Push Exerted by Secondary Object
Parallel to Secondary Object
Weight (Fg)
Long Range Force Exerted by Gravity on the Object
Toward the Center of the Earth

15. Forces and Motion Free Body Diagrams
Illustrate All Forces Acting on an Object

16. Forces and Motion
Combining Forces

17. Forces and Motion Friction Types Static Friction (fs) (Before motion)
Kinetic friction (fk)(After motion)
Rolling Friction
Reduced Area of Contact
Fluid Friction
Drag (fdrag)

18. Forces and Motion Earth’s Gravity
Force Pulling all Objects Toward the Center of the Earth
g is the acceleration of Gravity (-9.8 m/s2)
Galileo Galilei ( )

19. Newton’s Laws of Motion1

20. Forces and Motion Newton’s First Law of Motion
“Every Body Continues In Its State of Rest, Or of Uniform Motion In A Straight Line, Unless It is Compelled to Change That State by Forces Impressed Upon It.”

21. Forces and Motion Newton’s First Law of Motion
“Every Body Continues In Its State of Rest, Or of Uniform Motion In A Straight Line, Unless It is Compelled to Change That State by Forces Impressed Upon It.”
aka “The Law of Inertia”

22. Forces and Motion Inertia Equilibrium
The Tendency of an Object to Resist a Change in Movement
Equilibrium
Net Force = 0

23. Newton’s Laws of Motion2

24. Forces and Motion Newton’s Second Law of Motion
“The Acceleration of a Body is Directly Proportional to the Net Force Acting on the Body and Inversely Proportional to the Mass of the Body.”

25. Forces and Motion Newton’s Second Law of Motion
The Greater the Force on the Object, the Greater the Acceleration of the Object
The Greater the Mass of the Object, the Weaker the Acceleration of the Object

26. Forces and Motion Newton’s Second Law of Motion Force is Related to…
The Mass of the Object (m)
The Acceleration of the Object (a)

27. Forces and Motion Measurement of Force SI Units Mass - Kilogram (kg)
Distance - Meter (m)
Time - Second (s)

28. Forces and Motion Measurement of Force The Newton (N)
One Newton can accelerate 1 kg to 1 m/s2
N = 1 kg*m/s2

29. Forces and Motion Weight
The Force of the Acceleration of Gravity on the Mass of an Object

30. Newton’s Laws of Motion3

31. Forces and Motion Interaction Forces Newton’s Third Law of Motion
“When an Object Exerts a Force On a Second Object, That Second Object Exerts an Equal and Opposite Force On the First Object.”

32. Forces and Motion Interaction Forces Newton’s Third Law of Motion
“For Every Action There is an Equal and Opposite Reaction”

33. Forces and Motion Momentum
Product of an Object’s Mass and Its Velocity
Large Mass/ Low Velocity = Small Mass/ High Velocity

34. Inelastic collisions M1V1=M2V2 Example
A 4.5-kg ham is thrown into a stationary 15-kg shopping cart. At what speed will the cart travel if the ham had an initial speed of 2.2 m/s?

35. Forces and Motion Universal Forces Electromagnetic Electric Magnetism
Attract and Repel
Electric
Opposites Attract (Charged Particles)
Magnetism
Opposites Attract (Polarized Metal Molecules)
Nuclear
Strong and Weak in Nucleus of Atom
Gravity

36. Forces and Motion Gravity
Every Object in the Universe Attracts Every Other Object
Force Relative to the Inverse of the Distance
Proportional to Mass
Acts over Great Distances

37. Forces and Motion Orbits
Orbits are Maintained by the Velocity of the Object Perpendicular to Gravity
Centripetal Force

38. Forces and Motion
Homework