1. Forces and Newton’s Laws of Motion

2. Force…
A push or a pull.
Force is not a thing in itself, but rather an interaction between two objects.

3. Unit of Force The metric unit of force is the Newton (N)
1 Newton = 1 kilogram of mass being accelerated at 1 m/s2
Fnet = ma

4. Examples A Flag being blown by the wind
A jet engine propelling an airplane

5. Forces Push or a pull Vector quantity
Contact forces- arise from physical contact with each other
Field (Noncontact) forces- force exerted even when not in direct contact (ex. Gravity, electrical force, magnetic forces)

6. Weight VS Mass

7. Mass the amount of matter in an object a constant property
a measure of the inertia
measured in kilograms (kg)

8. Weight the force upon an object due to gravity measured in Newtons (N)
weight = mass  accel. due to gravity
Fw = mg
measured in Newtons (N)

9. Practice  The weight of a 10 kg brick is... A) 98 N B) 10 kg
C) 9.8 kg
D) 10 N
E) 98 kg

10. Mass and Weight
On the Moon, the force of gravity is only 1/6 as strong as on the Earth.
In space you are practically weightless but your mass remains unchanged.
Your mass does not depend on where your are.
e.g. Earth, Moon, or space

11. Normal Force
Normal Force (Fn)- contact force that always acts perpendicular to the surfaces that are touching

12. Tension
Tension (T)- force that acts through a solid object such as a rope or chain; directed along the rope and pulls equally on the objects on either end. .

13. Net Force Determined by combining ALL forces acting on an object.
Balanced = No Net Force = Fnet = 0 N
Determined by combining ALL forces acting on an object.
Zero net force = zero acceleration
If there is a net force, there will be an acceleration.
Unbalanced = Net Force = Fnet ≠ 0 N

14. Free-Body Diagram
Free-body diagrams are drawings used to show the relative magnitude and direction of all forces acting upon an object in a given situation.

15. Basic Force Diagrams
A Car on a Level Surface
All forces on the car are vertical, so no horizontal
force can be generated.
A Car on a Banked Turn
The normal force on the car due to the road is no longer
vertical, so a component of the normal force acts in the
horizontal direction.
Normal force (N) - contact pressure that pushes surfaces together.
It is easier to drag a light chair across a room than a heavy table.
This is because the weight of the table exerts a higher normal force.

16. Fee Body Diagram (FBD) The next five slides include examples of FBDs
Review each slide
Make a list of any questions you have about the slides… be sure to sketch the diagrams in your notes 

17. A book is at rest on a table

18. A girl is suspended motionless from a bar which hangs from the ceiling by two ropes.

19. An egg is free-falling from a nest in a tree. Neglect air resistance.

20. A flying squirrel is gliding (no wing flaps) from a tree to the ground at constant velocity. Consider air resistance.

21. A rightward force is applied to a book in order to move it across a desk with a rightward acceleration. Consider frictional forces. Neglect air resistance.

22. Real Life Application

23. Balanced Forces (zero net)

24. Unbalanced Forces (non-zero net)
Imagine pushing your text book so that it would slide across the desk…

25. Equilibrium
Balance
In regards to motion an object has constant velocity if it is in equilibrium.
NO acceleration.
Types:
Static Equilibrium
Dynamic Equilibrium

26. Equilibrium- net force is equal to zero

27. Friction
The force that opposes the motion between two surfaces that are in contact.
Friction is the "evil monster" of all motion. Regardless of which direction something moves in, friction pulls it the other way.
Move something left, friction pulls right. Move something up, friction pulls down.
It appears as if nature has given us friction to stop us from moving anything.
Friction is actually a force that “appears” when there is relative motion between two objects.
Although two objects might look smooth, microscopically, they are very rough and jagged.

28. Friction
A force that opposes motion. Friction acts in a direction opposite to the object's direction in motion. Without friction, the object would continue to move at a constant speed forever
Static Friction (Fs): when object is at rest
Kinetic Friction (Fk): when object is moving
Sliding Friction: when two surfaces slide one over the other
Rolling Friction: when two surfaces slide one over the other

29. Static Equilibrium Velocity is zero Examples:
Scales pushing up
Weighing yourself on a set of scales
Weight down
Car parked on an incline
Normal
Friction
Weight down

30. Dynamic Equilibrium Velocity is nonzero and constant Examples:
Driving at constant velocity
Normal up
Friction
Force from road
Air resistance
Weight down
Terminal velocity when parachuting
Weight down

31. Kinetic (sliding) Friction
The force between surfaces in relative motion
For the same object, why is the force of kinetic friction less than the force of starting friction?

32. Static (starting) Friction
The force that opposes the start of the motion.
Static means stationary ( not moving).

33. Science Friction
Friction (Ff)- contact force between two surfaces that always opposes motion
2 types
Static friction (Fs) = keeps an object from moving (must be overcome to move an object at rest
Kinetic friction (Fk) =acts when an object is moving
Kinetic friction is weaker than static friction
Fk< Fs

34. Friction is not always a bad thing!
Walking! Your foot pushes backwards and friction opposes it by pushing it forward

35. Coefficient of Friction
A constant that depends on the two surfaces in contact
Ff = FN
(mu)….coefficient of friction
Coefficient of Friction - Friction on an Incline

36. Acceleration << g
Terminal Velocity
Net Force
Acceleration = g
Velocity = 0
but motion is about to begin mg F
Acceleration < g
v increasing downward mg F
Acceleration << g
v still increasing downward
just not as rapidly as before mg F
Acceleration = 0
Terminal velocity mg

37. Falling with Air Resistance & Terminal Velocity
When falling the force of air resistance becomes large enough to balance the force of gravity.
At this instant in time, there is no net force — the object stops accelerating (see D below); terminal velocity has been reached.

38. More real life…