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Newton’s 1st Law:
More Practice
Newton’s 1st Law:
More Practice
Newton’s 1st Law:
More Practice
Newton’s 1st Law:
More Practice
Newton’s 1st Law:
More Practice
Newton’s 1st Law:
More Practice
Newton’s 1st Law:
More Practice
Newton’s 1st Law:
More Practice
Newton’s 1st Law:
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Newton’s 2nd Law of Motion: Student
Learning Goal
The student will be able to state Newton’s 2nd Law
and apply it in qualitative and quantitative terms
to explain the effect of forces acting on objects.
(B3.4)
nd
2
Newton’s
Law of
Motion and Weight
Newton’s Second Law of Motion
If the net force on an object is not zero, the
object will be accelerated in the direction of the
net force.
Newton’s Second Law of Motion
If the net force on an object is not zero, the
object will be accelerated in the direction of the
net force.

 Fnet
a
m
Newton’s Second Law of Motion
If the net force is not zero, the object will be
accelerated in the direction of the net force.

 Fnet
a
m
i.e. the more massive the object, the harder it is to
change its motion (the higher its inertia).
Newton’s Second Law of Motion
If the net force on an object is not zero, the
object will be accelerated in the direction of the
net force.

 Fnet
a
m


Fnet  ma
Weight
The formula F = ma can also be used to calculate
the weight Fg of an object
Weight
The formula F = ma can also be used to calculate
the weight Fg of an object, the magnitude of the
force of gravity acting on it
Weight
The formula F = ma can also be used to calculate
the weight Fg of an object, the magnitude of the
force of gravity acting on it, if the acceleration a
is . . .
Weight
The formula F = ma can also be used to calculate
the weight Fg of an object, the magnitude of the
force of gravity acting on it, if the acceleration a
is the acceleration due to gravity, g = 9.8 m/s2.
Fg  mg
Weight
The formula F = ma can also be used to calculate
the weight Fg of an object, the magnitude of the
force of gravity acting on it, if the acceleration a
is the acceleration due to gravity, g = 9.8 m/s2.
Fg  mg
(mass is measured in kg)
Weight
Fg  mg
Weight is therefore measured in Newtons.
And the direction of the force is always [down].
Weight: Example
What is the weight of a 140 kg person?
Weight: Example
What is the weight of a 140 kg person?
Givens : m  140 kg
g  9.8 sm2
Unknown : Fg  ?
Weight: Example
What is the weight of a 140 kg person?
Givens : m  140 kg
g  9.8 sm2
Unknown : Fg  ?
Select : Fg  mg


Solve : Fg  140 kg  9.8 sm2  1372 N