1. An object in mechanical equilibrium is stable, without changes in motion.

2. Applied Physics: Chapter 2 Review
45 points
You may use your notes!!!
13 multiple choice
7 true/false
1 problem

3. Applied Physics: Chapter 2 Review
A vector has both _______________ and _______________.
A scalar has only _______________.
Of the following quantities, circle the scalar quantities and underline the vector quantities.
temperature mass time speed gravity force

4. Applied Physics: Chapter 2 Review
What is another word for support force? ____________________________ 
_______________ occurs when all of the forces acting on an object are balanced.
The weight of a person can be represented by a vector pointing in which direction? _______________
A child hangs by a trapeze. She has a weight of 100N. What is the force on each of the two ropes holding up the trapeze? _______________
If an object being pushed across the floor has a constant, it is in _______________ equilibrium.
The sum of two or more vectors is called the _______________.
What is the magnitude and direction of the resultant of a 7.0N force downward and a 9.0N force upward? 

5. 2.1 Force
A force is needed to change an object’s state of motion.

6. A force is a push or a pull.
Net Force
A force is a push or a pull.
The combination of all forces acting on an object is called the net force.
The net force on an object changes its motion.
The scientific unit of force is the newton, abbreviated N.
Pounds and newtons are units of weight, which are units of force.

7. 2.1 Force
Net Force
The net force depends on the magnitudes and directions of the applied forces.

8. 2.1 Force
Net Force
The net force depends on the magnitudes and directions of the applied forces.

9. 2.1 Force
Net Force
The net force depends on the magnitudes and directions of the applied forces.

10. 2.1 Force
Net Force
The net force depends on the magnitudes and directions of the applied forces.

11. 2.1 Force
Net Force
The net force depends on the magnitudes and directions of the applied forces.

12. 2.1 Force
Net Force
The net force depends on the magnitudes and directions of the applied forces.

13. 2.1 Force
Force Vectors
A vector quantity needs both magnitude and direction for a complete description. Force is an example of a vector quantity.
A vector is an arrow that represents the magnitude and direction of a quantity.
A scalar quantity can be described by magnitude only and has no direction. Time, area, mass, and volume are scalar quantities.

14. Force Vectors This vector represents a force of 60 N to the right.

15. 2.1 Force
Force Vectors

16. Assignment Page 24 Check Concepts: Section 2.1 – Questions 1 →6
Due tomorrow

17. You can express the equilibrium rule mathematically as F = 0.
2.2 Mechanical Equilibrium
You can express the equilibrium rule mathematically as F = 0.

18. Mechanical equilibrium is a state where no physical changes occur.
Whenever the net force on an object is zero, the object is in mechanical equilibrium—this is known as the equilibrium rule.

19. The  symbol stands for “the sum of.” F stands for “forces.”
2.2 Mechanical Equilibrium
The  symbol stands for “the sum of.”
F stands for “forces.”
For a suspended object at rest, the forces acting upward on the object must be balanced by other forces acting downward.
The vector sum equals zero.

20. 2.2 Mechanical Equilibrium
The sum of the upward vectors equals the sum of the downward vectors. F = 0, and the scaffold is in equilibrium.

21. Assignment Page 24 Check Concepts: Section 2.2 – Questions 7 →10
Due tomorrow.

22. 2.3 Support Force Begin here 9/12
For an object at rest on a horizontal surface, the support force must equal the object’s weight.

23. 2.3 Support Force
What forces act on a book lying at rest on a table?
One is the force due to gravity—the weight of the book.
There must be another force acting on it to produce a net force of zero—an upward force opposite to the force of gravity.
The upward force that balances the weight of an object on a surface is called the support force.
A support force is often called the normal force.

24. 2.3 Support Force
The table pushes up on the book with as much force as the downward weight of the book.

25. The two forces add mathematically to zero.
2.3 Support Force
The upward support force is positive and the downward weight is negative.
The two forces add mathematically to zero.
Another way to say the net force on the book is zero is  F = 0.
The book lying on the table compresses atoms in the table and they squeeze upward on the book. The compressed atoms produce the support force.

26. 2.4 Equilibrium for Moving Objects
Objects at rest are said to be in static equilibrium; objects moving at constant speed in a straight-line path are said to be in dynamic equilibrium.

27. 2.4 Equilibrium for Moving Objects
An object moving at constant speed in a straight-line path is also in a state of equilibrium.
Once in motion, if there is no net force to change the state of motion, it is in equilibrium.

28. 2.4 Equilibrium for Moving Objects
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.

29. 2.4 Equilibrium for Moving Objects
If the desk moves steadily at constant speed, without change in its motion, it is in equilibrium.
Friction is a contact force between objects that slide or tend to slide against each other.
In this case, F = 0 means that the force of friction is equal in magnitude and opposite in direction to the pushing force.

30. 2.5 Vectors
begin here 9/16
To find the resultant of two vectors, construct a diagram where the two vectors are placed head to tail. The arrow drawn from the tail of the first to the head of the last represents the resultant.

31. 2.5 Vectors The sum of two or more vectors is called their resultant.
Combining vectors is quite simple:
If they are in the same direction, they add.
If they are in opposite directions, they subtract.
If they are perpendicular(90°), use Pythagorean theorem.

32. 2.5 Vectors
Resultant – Sum of 2 or more vectors.
Head to Tail Method (A + B)
Draw vector A to appropriate length in direction stated.
At end of vector A, Draw vector B.
Continue placing subsequent vectors at end of previous vectors.
Resultant is drawn as arrow (vector) from tail of first vector to head (point) of last vector.

33. 2.5 Vectors

36. Vector Addition Example:
A plane is being flown at 90 km/hr East while being blown by the wind at 50 km/hr South. What is the plane’s resultant velocity?

37. Vector Addition Example:

38. Vector Addition Example:
Solving for magnitude:
2 vectors being added + resultant form right triangle.
Pythagorean Theorem
R2 = (90 km/hr)2 +(50 km/hr)2
R = km/hr

39. Assessment Questions
When you hold a rock in your hand at rest, the forces on the rock
are mainly due to gravity.
are mainly due to the upward push of your hand.
cancel to zero.
don’t act unless the rock is dropped.

40. Assessment Questions
When you hold a rock in your hand at rest, the forces on the rock
are mainly due to gravity.
are mainly due to the upward push of your hand.
cancel to zero.
don’t act unless the rock is dropped.
Answer: C

41. Assessment Questions
Burl and Paul have combined weights of 1300 N. The tensions in the supporting ropes that support the scaffold they stand on add to 1700 N. The weight of the scaffold itself must be
400 N.
500 N.
600 N.
3000 N.

42. Assessment Questions
Burl and Paul have combined weights of 1300 N. The tensions in the supporting ropes that support the scaffold they stand on add to 1700 N. The weight of the scaffold itself must be
400 N.
500 N.
600 N.
3000 N.
Answer: A

43. Assessment Questions
Harry gives his little sister a piggyback ride. Harry weighs 400 N and his little sister weighs 200 N. The support force supplied by the floor must be
200 N.
400 N.
600 N.
more than 600 N.

44. Assessment Questions
Harry gives his little sister a piggyback ride. Harry weighs 400 N and his little sister weighs 200 N. The support force supplied by the floor must be
200 N.
400 N.
600 N.
more than 600 N.
Answer: C

45. Assessment Questions
When a desk is horizontally pushed across a floor at a steady speed in a straight-line direction, the amount of friction acting on the desk is
less than the pushing force.
equal to the pushing force.
greater than the pushing force.
dependent on the speed of the sliding crate.

46. Assessment Questions
When a desk is horizontally pushed across a floor at a steady speed in a straight-line direction, the amount of friction acting on the desk is
less than the pushing force.
equal to the pushing force.
greater than the pushing force.
dependent on the speed of the sliding crate.
Answer: B

47. Assessment Questions
When Nellie hangs at rest by a pair of ropes, the tensions in the ropes
always equal her weight.
always equal half her weight.
depend on the angle of the ropes to the vertical.
are twice her weight.

48. Assessment Questions
When Nellie hangs at rest by a pair of ropes, the tensions in the ropes
always equal her weight.
always equal half her weight.
depend on the angle of the ropes to the vertical.
are twice her weight.
Answer: C