The document discusses free-body diagrams (FBDs) as a tool to visualize forces acting on an object, highlighting the magnitude and direction of these forces through arrows. It explains the concepts of frictional forces, normal forces, and how they relate to static and kinetic friction, along with distinguishing balanced and unbalanced forces. Essential points include the relationship between normal force and weight, as well as the characteristics of stationary and moving objects in terms of friction.

1. Free-body
Diagram
Sir Emman Sano

6. FBD
Used to visualize force and its magnitude
and direction.
The size of the arrows reflects the amount
of force.
The direction of the arrow shows the
direction that the force is acting.
A square box is commonly used to
simplify the representation of the object.

7. Example:
A book is at rest
on a tabletop.
Diagram the forces
acting on the book.

8. Force in FBD: Frictional Force
and Normal Force

9. Force in FBD: Frictional Force
and Normal Force
• Frictional Force is the force that acts when
surfaces slide or tend to slide over one
another.
• The direction of frictional force is always
opposite the direction of motion.
• Stationary object with no applied force has
no friction force.

10. Force in FBD: Frictional Force
and Normal Force
• Static Force – is when force is applied and
the object gets disturbed, even if it does not
move, friction acts on it.
• The type of friction that opposes motion is
now identified as kinetic friction.
• Static is associated with a lack of movement,
while kinetic is characterized by movement.

11. Force in FBD: Frictional Force
and Normal Force
• Friction is not dependent on the speed and
surface area where the objects are in contact.
• Normal force is the support force of the surface
where the surface is resting or in contact.
• The surface always exerts an upward force on the
object that is equal in magnitude in magnitude
to the downward force of its weight.

12. Force in FBD: Frictional Force
and Normal Force
• Friction is not dependent on the speed and
surface area where the objects are in contact.
• Normal force is the support force of the surface
where the surface is resting or in contact.
• The surface always exerts an upward force on the
object that is equal in magnitude in magnitude
to the downward force of its weight.

13. FBD of Balanced Force
• The vertical component forces are the normal force
(FN) and the weight force (W).
• Since they are equal forces that act in opposite
directions, they are opposite signs.
• For the horizontal component forces, the applied
force (Fapp), which is directed to the right, balances
the frictional force (Ff).
• The object at a constant velocity has no acceleration.

14. FBD of Unbalanced Forces
• The forces on the y-axis, FN and W have the
same length of arrows oriented in opposite
directions. This means they have balanced forces.
• Fapp on the right is twice as long as the Ff on the
left.
• The left being negative and the right being
positive, the net force is, therefore, on the
positive x-direction.