Newton’s First Newton’s First Law of MotionLaw of Motion

Chapter 4, Section 2Chapter 4, Section 2

Pg. 130 - 135Pg. 130 - 135

Newton’s First Law of Newton’s First Law of Motion (Inertia)Motion (Inertia)

““An object at rest remains at rest, and An object at rest remains at rest, and an object in motion continues in an object in motion continues in motion with a constant velocity motion with a constant velocity

unless the object experiences a unless the object experiences a net net external forceexternal force.”.”

InertiaInertia is the tendency of an object to is the tendency of an object to maintain its state of motion.maintain its state of motion.

ForcesForces

Stationary Stationary ObjectObject

FFxx

An An applied external force (Fx)applied external force (Fx) greater than an object’s greater than an object’s natural natural resisting force (Fresisting force (Fr)r) will will cause the object to move. The cause the object to move. The forces are added together to forces are added together to get the get the net force (net force (ΣΣF).F).

FFrr

ΣΣFF

Newton’s First Law of Newton’s First Law of Motion (Cont.)Motion (Cont.)

Net external forceNet external force is total force is total force resulting from a combination of resulting from a combination of external forces on an object.external forces on an object.

When there is no change in When there is no change in motion, an object is said to be at motion, an object is said to be at equilibriumequilibrium. .

Example Problem:Example Problem:Four forces act on a hot-air balloon (shown below). Find the magnitude and direction of the resultant force on the balloon. 5120 N5120 N

4050 N4050 N

1520 N1520 N 950 N950 N

∑ F in X direction

1520 N – 950 N = 570 N Left∑ F in Y direction

5120 N – 4050 N = 1070 N Up

θ

570 N

1070 NF

F ² = (1070 N) ² + F ² = (1070 N) ² + (570) ²(570) ²

F= 1212 NF= 1212 Nθ = Tan θ = Tan ¹¹־־ ((10701070 N / 570 N) N / 570 N)θ = 62° up from the θ = 62° up from the horizontalhorizontal

Newton’ First Law of Newton’ First Law of Motion (Cont.)Motion (Cont.)

- Mass is also a measurement of - Mass is also a measurement of inertia.inertia.- The greater the mass of an The greater the mass of an object, the less it object, the less it accelerates under an applied accelerates under an applied force. Therefore the greater mass force. Therefore the greater mass has the greater inertia.has the greater inertia.

ΣF

ΣF