Download Newton`s First Law of Motion (Inertia)

Newton’s First Law of
Motion
Chapter 4, Section 2
Pg. 130 - 135
Newton’s First Law of Motion
(Inertia)
Inertia is the tendency of an object to
maintain its state of motion.
“An object at rest remains at rest, and an
object in motion continues in motion with a
constant velocity unless the object
experiences a net external force.”
Forces
Stationary Object
ΣF
Fx
Fr
An applied external force (Fx) greater
than an object’s natural resisting force
(Fr) will cause the object to move. The
forces are added together to get the net
force (ΣF).
Newton’s First Law of Motion
(Cont.)
 Net
external force is total force
resulting from a combination of
external forces on an object.
When there is no change in motion, an
object is said to be at equilibrium.
Example Problem:
Four forces act on a hot-air balloon (shown
below). Find the magnitude and direction of
the resultant force on the balloon.
∑ F in X direction
5120 N
1520 N – 950 N = 570 N Left
∑ F in Y direction
5120 N – 4050 N = 1070 N Up
1520 N
950 N
F ² = (1070 N) ² + (570) ²
F= 1212 N
1070 N
θ = Tan ‫־‬¹ (1070 N / 570 N)
θ = 62° up from the horizontal
4050 N
F
θ
570 N
Newton’ First Law of Motion (Cont.)
- Mass is also a measurement of inertia.
- The greater the mass of an object, the less it
accelerates under an applied force. Therefore
the greater mass has the greater inertia.
ΣF
ΣF