1. Physics: Principles with Applications, 6th edition
Lecture PowerPoints
Chapter 4
Physics: Principles with Applications, 6th edition
Giancoli
© 2005 Pearson Prentice Hall
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2. Chapter 4 Vocabulary Inertial Reference Frame
Reference frame which Newton’s First Law of Motion operates
Force
Fundamental forces
Normal force
Contact force
Frictional force
Net force

3. Inertia and Free Particle Model
Force – Push or pull on an object
Unit is newton (N)
Force is a derived SI unit – dimensions are kg m/s2
Types of Forces
Fundamental forces (all field forces)
Contact forces
Field forces

4. Inertia and Free Particle Model
Fundamental forces (weakest to strongest)
Gravity*
Acts between any two objects with mass
Acts at infinite distances
Weak interactive
Involved in some types of nuclear phenomena
Acts at distances up to m
Electromagnetic
Operates between electrically charged particles
Strong interactive
Holds nucleus of an atom together
Acts at distances up to m
*Einstein’s General Theory of Relativity states that gravity bends space around the object rather than attracting it

5. Inertia and Free Particle Model
Contact force
Acts between objects that are touching
Types of contact forces
Friction – Exists between two solid surfaces because even the smoothest surface is quite rough on a microscopic scale.
Dry friction arises from a combination of
inter-surface adhesion
surface roughness
surface deformation
surface contamination

6. Inertia and Free Particle Model
Contact force
Types of contact forces (continued)
Examples of friction
Dry friction – includes static friction and kinetic (sliding) friction
Static friction - on between two or more solid objects that are not moving relative to each other. 
Kinetic friction (sliding friction) - two objects are moving relative to each other and rub together 
Rolling resistance – force that resists the rolling of a wheel or other circular object along a surface caused by deformations in the object and/or surface
Air resistance - Opposes the motion of objects moving in air (examples: open parachute, sail on sailboat)

7. Inertia and Free Particle Model

8. Inertia and Free Particle Model
Contact force
Coefficients of friction (μk and μs)

9. Inertia and Free Particle Model
Contact force
Types of contact forces (continued)
Normal force – contact force that acts perpendicular to the common surface of contact
Example: Gravity acts on a book on a table, but the book does not fall through the table because of the normal force of the table pushing upward on the book

10. Inertia and Free Particle Model

11. Inertia and Free Particle Model
Contact force
Types of contact forces (continued)
Buoyancy – an upward force exerted by a fluid that opposes the weight of an immersed object.
Example: Boat floating in water

12. Inertia and Free Particle Model
Contact force
Buoyancy
Source:

13. Inertia and Free Particle Model
Contact force
Types of contact forces (continued)
Tension – Present in objects that have the property of elasticity (when you stretch them and let go, they return to their original size (example: rubber band)
Tension is high when object stretched
Tension is low when object not stretched
Tension is the same throughout the object

14. Inertia and Free Particle Model
Contact force
Tension example –
Source:

15. Inertia and Free Particle Model
Field force
a force acting on a particle at various positions in space
Field forces can affect an object without touching it
These are the fundamental forces

16. Inertia and Free Particle Model
Field force

17. Inertia and Free Particle Model
Newton’s First Law
In an inertial reference frame, an object either remains at rest or continues to move at a constant velocity, unless acted upon by a net force

18. Inertia and Free Particle Model
Mass
The measure of an object's resistance to acceleration (a change in its state of motion) when a force is applied.
Inertia
the resistance of any physical object to any change in its state of motion; this includes changes to its speed, direction or state of rest

19. Inertia and Free Particle Model
Newton’s Third Law
When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body.
Example:  As a car’s wheels spin, they grip the road and push the road backwards. Since forces result from mutual interactions, the road must also be pushing the wheels forward. The size of the force on the road equals the size of the force on the wheels (or car); the direction of the force on the road (backwards) is opposite the direction of the force on the wheels (forwards). 

20. Inertia and Free Particle Model

21. Inertia and Free Particle Model

22. Inertia and Free Particle Model

23. Inertia and Free Particle Model
Newton’s Law of Universal Gravitation
A particle attracts every other particle in the universe using a force that is directly proportional to the product of their masses* and inversely proportional to the square of the distance between them.
*Einstein discovered that the force depends on momentum and energy instead of mass

24. Inertia and Free Particle Model
Newton’s Law of Universal Gravitation
F is the force between the masses in newtons
G is the gravitational constant (6.674×10−11 N · (m/kg)2);
m1 is the first mass in kilograms
m2 is the second mass in kilograms
r is the distance between the centers of the masses in meters.

25. Inertia and Free Particle Model
Force diagrams
A diagram showing all the forces acting on an object, the force's direction and its magnitude (in a steady state condition; no acceleration of the system).
If there is more than one body, separate force diagrams should be used for each

26. Inertia and Free Particle Model
Force diagrams
A force diagram includes 
The body
May be a point or blob if there are no rotational effects
May be a sketch if the point of application of a force becomes crucial and has to be indicated on the diagram.
The external forces
the direction and the line of action
the magnitude
the point of application.
Force diagrams are also known as free body diagrams

27. Inertia and Free Particle Model
Force diagrams
Always include
Force of gravity
May include
Normal force (common surface)
Tension (elastic cord or cable)
Air resistance (if moving through air)
Friction (if there is normal force)

28. Inertia and Free Particle Model
Force diagrams (Free body diagrams)

29. Inertia and Free Particle Model
Force diagrams (Free body diagrams)

30. Inertia and Free Particle Model
Net force
The overall force acting on an object.

31. Inertia and Free Particle Model
Equilibrium
If the net force on an object is zero, the object is in equilibrium

32. Inertia and Free Particle Model Example

33. Inertia and Free Particle Model Example

34. Inertia and Free Particle Model Example