1. Chapter 2 Mechanical Equilibrium

2. Equilibrium refers to a condition of balance.
Things in mechanical equilibrium are stable, without changes in motion.
The rocks are in mechanical equilibrium. They will stay that way indefinitely unless an unbalanced external force would be needed to change their resting state.

3. 2.1 Force Force - is a push or pull
A force is needed to change an object’s state of motion
State of Motion may be one of two things:
At Rest
Moving uniformly along a straight-line path

4. Net Force
Net Force- is the combination of all forces acting on an object.
Applied forces result in net forces
The net force on an object changes its motion
Can add or subtract forces to get resultant net force
If forces acting on object equals zero then we say the net force acting on the object = 0
Scientific unit for force are Newtons (N)

5. Net Force – a closer look
Net Force depends on the magnitudes and directions of the applied forces.

6. Net Force – a closer look
Net Force depends on the magnitudes and directions of the applied forces.

7. Net Force – a closer look
Net Force depends on the magnitudes and directions of the applied forces.

8. Net Force – a closer look
Net Force depends on the magnitudes and directions of the applied forces.

9. Net Force – a closer look
Net Force depends on the magnitudes and directions of the applied forces.

10. Net Force – a closer look
Net Force depends on the magnitudes and directions of the applied forces.

12. Force and Net Force
When the girl holds the rock with as much force upward as gravity pulls downward, the net force on the rock is zero.

13. Tension and Weight
Downward force caused by Earth’s gravity is known as weight.
Upward “stretching force” is called tension. Ropes, chains, strings, etc…all can experience tension.
When you hang an object from a spring scale there are two forces acting on the object:
- force of gravity pulling down
- tension force pulling upward
When the two forces are equal and opposite in direction, their net force = 0N.

14. Force Vectors – visual representation of a quantity
Forces can be represented by arrows
length of arrow represents amount (magnitude) of the force
direction of arrow represents direction of the force
refer to these arrows as vectors, which represent both the magnitude and direction of a force.

15. Vector Quantity Scalar Quantity
needs both magnitude and direction for a complete description.
ex: force, velocity, momentum
can be described by magnitude only and has no direction
ex: temperature, speed, distance

16. Scalar or Vector Quantity?
Time Interval Mass Speed Velocity Temperature Displacement Acceleration
Click For The Answers
scalar
scalar
vector
scalar
vector
vector

17. 2.2 Mechanical Equilibrium
Mechanical Equilibrium is a state wherein no physical changes occur; it is a state of steadiness.
When net force equals zero, an object is said to be in mechanical equilibrium.
Expressed mathematically as the equilibrium rule: ΣF=0
Σ – Greek Letter, Stands for “ the sum of”
F - Stands for “forces”
0 - all the forces acting on something add vertically to zero

18. Mechanical Equilibrium- a closer look
The equilibrium rule explains how and why these men are able to remain balanced on their painting scaffold.

19. Mechanical Equilibrium- a closer look
Each man’s weight is represented with downward vectors. Additionally the scaffold they’re standing on has weight.

20. Mechanical Equilibrium- a closer look
The tension of the ropes holding both men and the scaffold is represented with the two upward arrows.

21. Mechanical Equilibrium- a closer look
The sum of the upward vectors equals the sum of the downward vectors. F = 0, and the scaffold is in Equilibrium.

22. 2.3 Support Force
Support Force- the upward force that balances the weight of an object on a surface.
The upward force balances the weight of an object
Support force often called normal force
For an object at rest on a horizontal surface, the support force must equal the object’s weight.
Support Force
Weight (due to gravity)

23. 2.3 Support Force
The upward support force is considered positive and the downward weight is considered negative.
The two forces add mathematically to zero.
Another way to say the net force on the book is zero is F = 0.
Support Force +2N
Weight N
+2N – 2N = 0
0N = Rest

24. 2.4 Equilibrium of Moving Objects
Equilibrium can exist in both objects at rest and objects moving at a constant speed, in a straight-line path.
Equilibrium means state of no change.
Sum of forces equal zero
When the push on the desk is the same as the force of friction between the desk and the floor, the net force is zero and the desk slides at an unchanging speed.

25. Equilibrium of Moving Objects
Static Equilibrium
Dynamic Equilibrium
Objects at rest are said to be in static equilibrium.
Objects moving at a constant speed in a straight- line path are said to be in dynamic equilibrium.

26. 2.5 Vectors Parallel Vectors Add vectors if in same direction
Subtract vectors if in opposite direction
The sum of two or more vectors is called the resultant
same direction- add
opposite direction- subtract

27. 2.5 Vectors Non- Parallel Vectors The Parallelogram Rule
- To find the resultant of nonparallel vectors, we use the parallelogram rule.
- Consider two vectors at right angles to each other, as shown below. The constructed parallelogram in this special case is a rectangle. The diagonal is the resultant R.

28. Applying the Parallelogram Rule
When Nellie is suspended at rest from the two non-vertical ropes, is the rope tension greater or less than the tension in two vertical ropes?
You need to use the parallelogram rule to determine the tension.
Notice how the tension vectors form a parallelogram in which the resultant R is vertical.

29. Applying the Parallelogram Rule
Think!
Two sets of swings are shown at right. If the children on the swings are of equal weights, the ropes of which swing are more likely to break?

30. Applying the Parallelogram Rule
Think!
Two sets of swings are shown at right. If the children on the swings are of equal weights, the ropes of which swing are more likely to break?
Answer: The tension is greater in the ropes hanging at an angle. The angled ropes are more likely to break than the vertical ropes.
- As Angles Increase, Tension Increases
CLICK FOR ANSWER

31. Chapter 2 Mechanical Equilibrium

32. Equilibrium refers to a __________________________
Things in mechanical equilibrium are stable, without changes in motion.
The rocks are in mechanical equilibrium. They will stay that way indefinitely unless an unbalanced external force would be needed to change their resting state.

33. 2.1 Force Force - ___________________________
A force is needed to change an object’s ______________________
State of Motion may be one of two things: .

34. Net Force Net Force- ___________________
________________________________
Applied forces result in net forces
The net force on an object changes its motion
Can add or subtract forces to get ______________ net force
If forces acting on object equals zero then we say the net force acting on the object = 0
Scientific unit for force are ___________________( )

35. Net Force – a closer look
Net Force depends on the ________________and _________________of the applied forces.

36. Net Force – a closer look
Net Force depends on the magnitudes and directions of the applied forces.

37. Net Force – a closer look
Net Force depends on the magnitudes and directions of the applied forces.

38. Net Force – a closer look
Net Force depends on the magnitudes and directions of the applied forces.

39. Net Force – a closer look
Net Force depends on the magnitudes and directions of the applied forces.

40. Net Force – a closer look
Net Force depends on the magnitudes and directions of the applied forces.

42. Force and Net Force
When the girl holds the rock with as much force upward as gravity pulls downward, the net force on the rock is zero.

43. Tension and Weight
Downward force caused by Earth’s gravity is known as ______________.
Upward “stretching force” is called ___________ Ropes, chains, strings, etc…all can experience tension.
When you hang an object from a spring scale there are two forces acting on the object:
- force of gravity pulling ____________
- tension force pulling ______________
When the two forces are equal and opposite in direction, their net force = 0N.

44. Force Vectors – visual representation of a quantity
Forces can be represented ____________________________
length of arrow represents ___________________________________
direction of arrow represents _________________________________
refer to these arrows as vectors, which represent both the magnitude and direction of a force.

45. _________________ __________________
needs both magnitude and direction for a complete description.
ex: force, velocity, momentum
can be described by magnitude only and has no direction
ex: temperature, speed, distance

46. Scalar or Vector Quantity?
_________
Time Interval Mass Speed Velocity Temperature Displacement Acceleration
_________
_________
_________
_________
_________
_________

47. 2.2 Mechanical Equilibrium
__________________________ is a state wherein no physical changes occur; it is a state of steadiness.
When net force equals zero, an object is said to be in mechanical equilibrium.
Expressed mathematically as the equilibrium rule: ΣF=0
Σ – ________________________________
F - _____________________
0 - ________________________________

48. Mechanical Equilibrium- a closer look
The equilibrium rule explains how and why these men are able to remain balanced on their painting scaffold.

49. Mechanical Equilibrium- a closer look
Each man’s weight is represented with downward vectors. Additionally the scaffold they’re standing on has weight.

50. Mechanical Equilibrium- a closer look
The tension of the ropes holding both men and the scaffold is represented with the two upward arrows.

51. Mechanical Equilibrium- a closer look
The sum of the upward vectors equals the sum of the downward vectors. F = 0, and the scaffold is in Equilibrium.

52. 2.3 Support Force
Support Force- the upward force that balances the _______________________________________________________.
The upward force balances the weight of an object
Support force often called ________________________
For an object at rest on a horizontal surface, the support force must equal the object’s weight.
Support Force
Weight (due to gravity)

53. 2.3 Support Force
The upward support force is considered _________ and the downward weight is considered ____________.
The two forces add mathematically to zero.
Another way to say the net force on the book is zero is F = 0.
Support Force +2N
Weight N
+2N – 2N = 0
0N = Rest

54. 2.4 Equilibrium of Moving Objects
Equilibrium can exist in objects both at rest and objects moving at a constant speed, in a straight-line path.
Equilibrium means state of no change.
Sum of forces equal zero
When the push on the desk is the same as the force of friction between the desk and the floor, the net force is zero and the desk slides at an unchanging speed.

55. Equilibrium of Moving Objects
_______________________
_______________________
Objects at rest are said to be in static equilibrium.
Objects moving at a constant speed in a straight- line path are said to be in dynamic equilibrium.

56. 2.5 Vectors Parallel Vectors Add vectors if in same direction
Subtract vectors if in opposite direction
The sum of two or more vectors is called the resultant
same direction- add
opposite direction- subtract

57. 2.5 Vectors Non- Parallel Vectors The Parallelogram Rule
- To find the resultant of nonparallel vectors, we use the parallelogram rule.
- Consider two vectors at right angles to each other, as shown below. The constructed parallelogram in this special case is a rectangle. The diagonal is the resultant R.

58. Applying the Parallelogram Rule
When Nellie is suspended at rest from the two non-vertical ropes, is the rope tension greater or less than the tension in two vertical ropes?
You need to use the parallelogram rule to determine the tension.
Notice how the tension vectors form a parallelogram in which the resultant R is vertical.

59. Applying the Parallelogram Rule
Think!
Two sets of swings are shown at right. If the children on the swings are of equal weights, the ropes of which swing are more likely to break?

60. Applying the Parallelogram Rule
Think!
Two sets of swings are shown at right. If the children on the swings are of equal weights, the ropes of which swing are more likely to break?
Answer: