Snapshot 1
Consider the hover disk sitting on
the floor.
Force Diagram
(Free-Body Diagram)
Constant Velocity
Balanced Forces

FN

FN
Floor

Fg
Hover
Disk

Fg
Earth
FN  Fg
Snapshot 2
The hover disk is moving to the
right while on.
Constant Velocity
Balanced Forces

FN

FN
Floor

Fg
Hover
Disk

Fg
Earth
FN  Fg
Snapshot 3
The hover disk is sliding to the
right while off.
Changing Velocity
Unbalanced Forces

FN

FN
Floor

F fk
Hover
Disk

Fg
Earth

F fk

Fg
Snapshot 4
The hover disk is pulled to the right
while on.
Changing Velocity
Unbalanced Forces

FN

FN
Floor

FT

FT
Hover
Disk

Fg
Earth
String

Fg
Do you see a pattern between the type of motion
and whether or not the forces are balanced?
Snapshot 2
Snapshot 3
Snapshot 4
Constant Velocity
Constant Velocity
Changing Velocity
Changing Velocity
Balanced Forces
Balanced Forces
Unbalanced Forces
Unbalanced Forces
FN  Fg
FN  Fg

FN

FN
Snapshot 1

Fg

Fg

FN

F fk

FN

FT

Fg

Fg
Sir Isaac Newton (December 25th, 1642-1727)
Newton’s First Law of Motion – Objects move with constant velocity when the
forces are balanced and move with changing
velocity when the forces are unbalanced.