Download Newton second Law of Motion HP 1314

Newton’s
Second Law of
Motion
Newton’s Second Law
Part 1:
The net force on an
object causes its
acceleration.
Net Force
 Net
Force, Total Force,
Resultant Force
ΣF = F1 +F2 + F3 + …
Fnet = F1 + F2 + F3 + …
Mechanical Equilibrium
 The
resultant force is zero
 All forces cancel out
 There is no change in the objects
motion
Car at Constant Speed
ΣF =
Normal Force = 2000 N
Fa = 50 N
Friction = 50 N
Weight = 2000 N
Net Force Causes
Acceleration
• To increase the acceleration of an object,
you must increase the net force acting on
it.
• An object’s acceleration is directly
proportional to the net force acting on it:
acceleration ~ net force
(The symbol ~ stands for “proportional to.”)
Newton’s Second Law
Part 2:
The mass of an object
resists acceleration.
Mass Resists
Acceleration
• The same force applied to twice as much
mass results in only half the acceleration.
• The acceleration is inversely proportional to
the mass.
Newton’s Second LawNet Force causes acceleration,
mass resists it.
a = Fnet
m
or
Fnet = ma
Force is measured in
Newtons;
2
(1.00kg)(1.00m/s )= 1 N
(Newton)
do the math!
A car has a mass of 1000 kg. What
is the acceleration produced by a
force of 2000 N?
If the force is 4000 N, what is the
acceleration?
do the math!
How much force, or thrust, must a
30,000-kg jet plane develop to
achieve an acceleration of 1.5
m/s2?
10 N
20 N
20 kg
a = 0.50
2
m/s right
Free Fall Explained
How come all objects
free fall with the same
acceleration?
Free Fall Explained
As the gravitational force (weight) on
an object increases, so does its mass.
Net Force causes
acceleration and
mass resists
Mass and Weight
Mass is not Weight
 Mass
is the quantity of matter in
an object.
 Weight is the force of gravity on
an object.
Common Forces
 Names
of some common forces
 Tension
 Normal/Support Force
 Gravitational Force/Weight
 Friction
 Applied force
Free-Body Diagrams
Normal
N
mg
mg
You can safely hang from a clothesline
hanging vertically, but you will break the
clothesline if it is strung horizontally.