- A force is a push or pull on an object due to its interaction with other objects. Common forces include gravity, normal force, tension, friction, electromagnetic force, and contact force. - Forces are represented by arrows, with the length proportional to the magnitude. Forces can be added vectorially to find the net/resultant force. If the net force is nonzero, the object will accelerate. If it's zero, the object will maintain a constant velocity or remain at rest. - For every action there is an equal and opposite reaction. The forces due to interactions between two objects are always equal in magnitude and opposite in direction.

2. A force is a pull or a push that
an object experiences due to its
interaction with other objects.

3.  Symbol:
 SI-unit:
 Vector
 1𝑁 = 1 𝑘𝑔 ∙ 𝑚 ∙ 𝑠−2
𝑭
Newton (N)

5. A force is exerted on an
object by someone

6. - A force exerted by a rope or
cable when it is pulled.
- The same everywhere in the
rope/cable.

7. A force between and object and the
surface on which it rests parallel to
the surface.
Always opposes motion
𝒗

8. - The force that a surface exerts on the
object that rests on it.
- Always perpendicular from the surface
on the object.

9. The force with which the earth
attracts an object
- Always downwards
- 𝐹 𝑔 = 𝑚 𝑔
where 𝑔 = 9,8 𝑚 ∙ 𝑠−2
𝑚 = 𝑚𝑎𝑠𝑠 (𝑘𝑔)

10. The force that magnets exert on
other ferromagnetic objects.
- Repulsive or Attractive

11. - The force that charged objects exert
on other objects
- Repulsive or Attractive

12. Identify all the forces present in the
following pictures:

13.  The object itself is represented
diagramatically
 Forces are shown with arrows
where it really works on the object.
 Lengths of the arrows shows the
relative magnitudes of the forces

14. Draw a force diagram that shows all the
forces that are exerted on the trolley
𝑭 𝒈
𝑭 𝑵
𝑭 𝑻
𝒇
𝑭 𝑷𝒍𝒂𝒏𝒕𝒆
𝑭 𝑻𝒙
𝑭 𝑻𝒚

15.  FREE OF A BODY
 Object represented by only a dot
 All arrows must point from the dot
outwards
 Lengths of the arrows shows the
relative magnitudes of the forces

16. Draw a free body diagram that shows
all the forces exerted on the trolley
𝑭 𝑵
𝑭 𝑻
𝒇
𝑭 𝑷𝒍𝒂𝒏𝒕𝒆
𝑭 𝑻𝒙
𝑭 𝑻𝒚𝑭 𝒈

17.  All the forces exerted on a certain
point cancel each other
 The resultant of the forces are zero
 The object remains in rest or moves
with a constant velocity
 When all the forces are drawn head
to tail it forms a CLOSED vector
diagram.

19. When three forces that are
exerted on the same point
are in equilibrium, their
magnitudes and direction
can be shown by the three
sides of a triangle.

20. Objects in rest Moving Objects
Changes as the
applied force
changes
Always constant
𝒇 𝒌𝒇 𝒔
𝒇 𝒌 = 𝝁 𝒌 𝑭 𝑵𝒇 𝒔 𝒎𝒂𝒙 = 𝝁 𝒔 𝑭 𝑵

21. 𝒇 𝒔 𝑭 𝑻
𝒇
𝑭 𝑻
𝒇 𝒌
𝒗 = 𝟎 𝒗 > 𝟎
𝒇 𝒔 𝒇 𝒌𝒇 𝒔 𝒎𝒂𝒙

22.  The static friction that an object
experiences just before it moves.
 Static friction increases as the force it
opposes increases, until it reaches a
maximum.
 If the applied force increases further, the
object starts to move.
 The object now experiences kinetic friction.

23. 𝒇 = 𝝁𝑭 𝑵

24.  Strongly dependent on surface roughness.
 Directly proportional to the normal force.
 Indipendent on the surface area of the
surfaces in contact.
 Kinetic friction is independent of the speed
at which the object moves.
 Only the maximum static friction can be
calculated with a formula
 𝒇 𝒌 < 𝒇 𝒔 𝒎𝒂𝒙

25.  μ
 No unit
 Property of the surfaces in contact
 Mostly smaller than one
 The bigger μ, the bigger the friction
 𝜇 𝑘 < 𝜇 𝑠

26. The net force of all the forces
that are exerted on an object,
is the vector sum of all the
forces that are exerted on the
object.

27.  Also known as the resultant force

 The net forces in the x-axis an
y-axis are calculated separately
 Inclined forces are separated into
perpendicular components.
𝑭 𝑵𝑬𝑻
𝑭 𝑵𝑬𝑻 𝒙 = 𝑭 𝒙 𝑭 𝑵𝑬𝑻 𝒚 = 𝑭 𝒚

28. A book is pulled over a rough surface
with a constant force. The kinetic
friction coefficient between the surface
and the book is 0,5. All the forces are
in equilibrium.
a) Draw a free body diagram
b) Determine the normal force
c) Calculate the kinetic friction
d) Calculate the applied force

29. The same book as in the previous
example is now being pulled across
the table by an 5 N force, that makes
an angle of 30° with the horizontal.
a) Calculate the kinetic friction.
b) How does the value of the friction
compare to the value in the
previous exmaple? Explain.
c) Calculate the net force in the x-axis

30. 𝑭 𝒈
θ
𝒇
𝑭 𝑵
𝑭 𝑻

31. θ
θ
𝑭 𝒈
𝑭 𝒈⊥
𝑭 𝒈∥
𝒔𝒊𝒏𝜽 =
𝑭 𝒈∥
𝑭 𝒈
𝑭 𝒈∥ = 𝑭 𝒈 𝒔𝒊𝒏𝜽
𝑭 𝒈⊥ = 𝑭 𝒈 𝒄𝒐𝒔𝜽
𝒄𝒐𝒔𝜽 =
𝑭 𝒈⊥
𝑭 𝒈
90°

32. All the forces exerted on the crate in
the diagram are in equilibrium. Answer
the following questions:
a) Draw a free body diagram.
b) Calculate and .
c) Calculate the normal force.
d) Calculate the kinetic friction.
e) Calculate
𝑭 𝒈∥ 𝑭 𝒈⊥
𝝁 𝒌

33. 5 kg
25°

36. If object A exerts a force on
object B, object B will exert a
force on object A that has the
same magnitude, but opposite
direction.

38. A B
A:
𝑭 𝒈
𝑭 𝑵
𝒇
𝑭 𝑩𝑨 𝑭 𝑻
𝑭 𝑵
𝒇
𝑭 𝒈
𝑭 𝑨𝑩
B:
𝑭 𝑻

39.  but opposite in
direction
 Is NOT exerted on the same
object
 Do NOT cancel eachother
 Works SIMULTANEOUSLY
- THEREFORE:
For each action there is a reaction
𝑭 𝑨𝑩 = 𝑭 𝑩𝑨

40. Identify the Newton III force pairs
in the following diagram.

41. A:
𝑭 𝒈
𝑭 𝑵
𝒇
𝑭 𝑩𝑨 𝑭 𝑻
𝑭 𝑵
𝒇
𝑭 𝒈
𝑭 𝑨𝑩
B:
Newton III Force Pairs

42. An object will remain in a state of
rest, or move with a constant
velocity in a straight line, unless a
net force is exerted on the object.

43. In Symbols:
𝑭 𝑵𝑬𝑻 = 𝟎 𝑵
if
𝒗 = 𝟎 𝒎 ∙ 𝒔−𝟏
∴ 𝒂 = 𝟎 𝒎 ∙ 𝒔−𝟐
𝒗 = 𝒄𝒐𝒏𝒔𝒕𝒂𝒏𝒕

44. The property of an object that
causes it to resist a change in its
state of motion

45.  A property of the object
 All objects with mass have
innertia
 Bigger mass = More innertia

46. If a net force is exerted on an
object, the object will accelerate in
the direction of the force. The
acceleration is directly proportional
to the force and inversely
proportional to the mass of the
object.

47. In Symbols:
𝑭 𝑵𝒆𝒕 = 𝒎𝒂
where 𝑭 𝑵𝑬𝑻 = 𝑵𝒆𝒕 𝑭𝒐𝒓𝒄𝒆 (𝑵)
𝒎 = 𝒎𝒂𝒔𝒔 (𝒌𝒈)
𝒂 = 𝒂𝒄𝒄𝒆𝒍𝒆𝒓𝒂𝒕𝒊𝒐𝒏 (𝒎 ∙ 𝒔−𝟐
)

48. 𝒂 ∝ 𝑭 𝑵𝑬𝑻
Direct proportionality
=
Straight line through
origin
𝒂
𝑭 𝑵𝑬𝑻

49. 𝒂 ∝
𝟏
𝒎
Inverse proportionality
=
Hyperbole
𝒂
𝒎

50. 𝒂
𝟏
𝒎
𝒂 ∝
𝟏
𝒎
Straight line

51. 1) Separate inclined forces into
perpendicular components
2) Draw free body diagrams
3) Identify the applicable axis. Handle
the x-axis and y-axis separately.
4) Obtain an equation for 𝑭 𝑵𝑬𝑻

52. 𝒗 = 𝟎 𝒎 ∙ 𝒔−𝟏
Newton I Newton II
𝒂 ≠ 𝟎 𝒎 ∙ 𝒔−𝟐
5) Decide which law you will use:
𝑭 𝑵𝑬𝑻 = 𝟎 𝐍 𝑭 𝑵𝑬𝑻 = 𝒎𝒂
𝒗 = 𝒄𝒐𝒏𝒔𝒕𝒂𝒏𝒕

53. 6) Check for friction:
μ is given
YES NO
Calculate with:
𝑭 𝑵𝑬𝑻 = 𝑭
Calculate 𝑭 𝑵
Calculate with:𝒇
𝒇 = 𝝁𝑭 𝑵
𝒇

54. A Block, mass 5 kg, is being pulled
across a horizontal table with a constant
force of 50 N. The magnitude of the
friction is, 20 N. Calculate:
a) The acceleration of the block.
b) The friction coefficient between the
block and the table.

55. A boy pushes a crate of 50 kg over the
floor with the aid of a rod that makes an
angle of 40° with the horizontal. He
exerts a force of 300 N on the rod. The
friction coefficient between the crate and
the floor is 0,2.

56. a) Calculate the friction between the
floor and the crate.
b) Calculate the acceleration of the
crate.
300 N
40°

57. A person ski’s down a slope that makes an
angle of 40° with the horizontal. The total
mass of the skier and his ski’s is 50 kg. The
friction coefficient between the snow and the
ski’s are 0,1.
a) Calculate the net force the person
experience parallel to the surface.
b) Calculate the acceleration of the skier.

58. The diagram shows a 3 kg block (B) and
a 2 kg block (A) that is being pushed
forward by a force of 30 N so that the
system accelerates to the right. The
applied force makes an angle of 15° with
the horizontal. Each block experiences a
friction force of 5 N.

59. 15°
a) Calculate the acceleration of the
system.
b) Calculate the force that A exerts on B.
c) Calculate the force that B exerts on A.
A B

60. B
6 kg
A
4 kg
C
6 kg
T1 T2

61. The friction coefficient between Block B
and the table top is 0,034. Assume that
the ropes have negligible mass and that
the pulleys are frictionless. Calculate:
a) The acceleration of the system.
b) The tension in the ropes..

62. A man with a mass of 70 kg stands on a
scale in a lift. Calculate the reading on the
scale if the lift:
a) Is in rest.
b) Moves upward with a constant velocity
of 3,2 m·s-1.
c) Accelerates upward at 3,2 m·s-2.
d) Accelerates downward at 3,2 m·s-2.
e) Freefall

63. Between any two objects with mass
there exist a gravitation force that is
directly proportional to the product of
their masses and inversely
proportional to the square of the
distance between their centre points.

64. 𝑭 𝑮 = 𝑮
𝒎 𝟏 𝒎 𝟐
𝒓 𝟐
𝒓𝒎 𝟏 𝒎 𝟐

65.  𝐹𝐺 = Gravitation force (N)
 𝑚1; 𝑚2 = Mass of objects (kg)
 𝑟 = Distance between objects (m)
 𝐺 = Universal Gravitation Constant
= 6,67 x 10-11 N·m2·kg-2
𝑭 𝑮 = 𝑮
𝒎 𝟏 𝒎 𝟐
𝒓 𝟐

66. 𝑭 𝑮 = 𝑮
𝒎𝑴
𝑹 𝟐
 𝑀 = Massa van planeet (kg)
 𝑚 = Massa van vorrwerp (kg)
 𝑅 = Radius van planeet (m)

67. 𝑭 𝑮 = 𝑮
𝒎𝑴
𝑹 𝟐
Attraction force by earth on object:
𝑭 𝒈 = 𝒎𝒈 and
𝑭 𝑮 = 𝑭 𝒈but

68. 𝑮
𝒎𝑴
𝑹 𝟐
= 𝒎𝒈therefore ÷ 𝒎
𝒈 = 𝑮
𝑴
𝑹 𝟐

69.  Amount of matter
 Symbol: m
 Unit: kg
 Scalar
 The same everywhere

70.  Force with which planets
attract an object
 Symbol: 𝐹𝑔
 Unit: N
 Vector
 Function of the mass and
radius of a planet

71. Two spherical objects m1 and m2, with
their centre points a distance r metre
apart, exerts a gravitation force of 6 N on
each other. Determine the magnitude of
the force if:
a) The mass m1 doubles.
b) The distance between them halves.

72. Two metal spheres with masses
8 x 104 kg and 2 x 103 kg respectively is
placed 340 cm apart. Calculate the
gravitation force between them.

73. An astronaut with a mass of 80 kg on the
earth lands on planet X with his spaceship.
Planet X has a radius that is half that of the
earth ant a mass that is double that of the
earth.
a) Calculate the value of g on planet X.
b) Calculate the garvitation force that the
man experiences on planet X.