Download Sections 2.6 and 2.7

Review- What is
happening in this video?
How?
http://player.discoveryeducation.com/index.cfm?guidAssetId=69D515CC-CFDF-4DB2-9F6D386F68CD4E02&blnFromSearch=1&productcode=US#
Objectives
Review- Entrance Ticket.
Weight Vs. Mass
Distinguish between force and net
force.
Equilibrium rule.
Weight
VS.
 Force of gravity acting
on an object

http://www.explorat
orium.edu/ronh/weight/
index.html
MASS
 Amount of Matter an
object contains
What is Force?
 Force is a Push or a Pull
 Forces are vector quantities - they have a
magnitude (How Much) and a direction
Ex.: 10 N to the right

Forces are shown with arrows
Point in the direction which it is being applied.
The length of the arrow shows the magnitude
(how much) of the force.
Net Force (Unbalanced Force)




Total force being exerted on an object.
Ex. Pull a box w/ net force of 5 N,
A Friend pulls a box w/ net force of 5 N
How much total force is being pulled?
Net Force
 If no forces act on an object, the net force on the object is zero.

Additional Examples-

http://www.batesville.k12.in.us/physics/phynet/mechanics/newton1/the_net_force.html
Net Force Activity
Normal Force
 The force on an
object that is in
contact with a
surface
– It is perpendicular to
the surface
– It usually is the force
opposite of the
weight of the object.
Equilibrium
When the net force on something is zero:
That something is in mechanical equilibrium.
What is equilibrium?
Equilibrium means a state of physical balance.
Equilibrium
Equilibrium Rule:
∑F=0
∑ stands for the “vector sum of”
F stands for “forces”
Equilibrium
Equilibrium Rule Continued:
The rule says that the forces acting in one direction on
an object must be balanced by forces acting in the
opposite direction.
Example: Forces acting upward must be balanced by forces
acting downward.
In essence, they must cancel each other out.
Static Equilibrium
 Static means “not
moving.”
 If an object is not moving,
it is in static equilibrium
– This means that the
weight of the object is
canceled out by the
normal force.
Dynamic Equilibrium
 Dynamic means
“moving.”
 An object is in dynamic
equilibrium when it is
moving with a constant
velocity.
– Example – The force
applied to the car is equal
to the friction acting
against it.