What is a FORCE?
 A force is a
another object
 Force is a
or
from an object interacting with
quantity with
.
The Units for Force:
TYPES OF FORCES
Forces can be classified in one of two categories: contact forces and action-at-a-distance forces.
CONTACT FORCES
APPLIED FORCE,
NORMAL,
FORCE OF GRAVITY,
a
FORCE OF TENSION,
ACTION-AT-A-DISTANCE FORCES
T
g
,
(For Earth and objects on the surface of the Earth,
Fg points toward the centre of the Earth)
To calculate use:
g = m
2
= 9.8 m/s [down]
N
What is weight?
FORCE OF FRICTION,
f
ELECTRIC FORCE
MAGNETIC FORCE
FORCE DIAGRAMS
To understand forces and how they affect motion, you need to draw diagrams that show which
forces are acting on an object. There are two types of diagrams used for force questions:
SYSTEM DIAGRAM
FREE BODY DIAGRAM (FBD)
Example 1: Draw the system diagram and an FBD for each situation below.
(A) A book on a desk
(B) A book on a desk
(C) A wagon that is
(D) A skier skiing
(not moving)
that is pushed
being pulled by a rope down a slope
Net Force,
net
Example 2: Calculate the net force on a 5 kg book pushed on a desk with a force of 5.5 N [W].
The force of friction on the book is 3.5 N and the normal force is 49 N. Draw the FBD.
.
THE FUNDAMENTAL FORCES
Four categories of forces in which all natural forces are categorized:
FUNDAMENTAL
FORCES
RELATIVE
STRENGTH
GRAVIATIONAL
1
ELECTROMAGNETIC
1020
STRONG NUCLEAR
1038
WEAK NUCLEAR
1025
DESCRIPTION
HOMEWORK: Read Pages 114-121 and Complete Questions #1-5, 7-11, 14-16 on Page 122