Download Newton`s 2nd Law of Motion - Garnet Valley School District

Newton’s 2nd Law of
Motion
Forces
• A ______or _______
• The cause of an ____________
• Cause of a change in an object’s state of
motion
• Cause objects to ___________ or
______________
• Cause a change of _____________
• Unit of force: _______________
Free Body Diagrams
• One object ______
• Forces represented as arrows
placed where they _________
• Length of the arrows should
represent the _____________of
the force
• Fg down, FN perpendicular to
surface, Ff parallel to surface
opposing motion
Free Body Diagrams
• Used to analyze the forces affecting
the motion of a single object
• Shows only the forces acting on an
object
Finding Fnet
• We define forces pointing up or right as
_______________
• We define forces pointing left or down as
_____________
• To get Fnet:
• Add all parallel forces and subtract off
antiparallel forces
Example
A mover pushes a box with a 20 Newton force to the right.
His friend sees him struggling so he helps push the box by
applying a 25 Newton force in the same direction.
What is the net force on the box?
Example
• Now a 3rd mover, not being too bright, decides to help
by pushing with a 14 Newton force in the opposite
direction. What is the net force now?
Newton’s 2nd Law
• The acceleration of an object is directly
proportional to the net external force
acting on the object and inversely
proportional to the mass of the object
or:
____________
Types of Forces
• Contact forces:
• _____________- (Ft or T) - The force
that a “string” pulls on an object
• _______________- (FN or N) - Force
that a surface applies to an object
(the direction is  to the surface)
• __________- (Ff) - To be defined later
F, applied force
 A physical push or a pull
FN, Normal Force (N)
• A force that a surface applies to an
object
• “Normal” means ______________
• The direction of the normal force is
perpendicular to the ____________
surface
Tension - (Ft or T)
 Tension (force) in a string
or rope
 Strings only ________
Types of Forces
• Field Forces (Action at Distance)
• Force of _________(Fg) or Weight
• Fg =_______, - WEIGHT IS THE FORCE
OF GRAVITY
• ___________
• Where g = _____________
• Electricity/Magnetism
Force of Friction Ff
• Always parallel to the surface
• Acts opposite to the direction of motion
F f = μ FN
Where μ is the coefficient of friction
It is determined between the two surfaces in contact (it will vary
depending upon the surface)
Common μ’s
Materials
Oak on oak, dry
μ
0.30
Steel on steel,
dry 0.41
greasy 0.12
Steel on ice
Rubber on asphalt,
0.01
Dry 1.07
wet 0.95
Rubber on ice
0.005