Download Chapter I: Concepts of Motion

Free body diagram (FBD)
Zero net Force implies constant velocity
Identifying Forces acting on an
object
Free Body Diagram (FBD)
What is the “natural state” of
matter?
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Aristotle (384 – 322 BCE)
• Natural state of matter is to be “at rest”
• What force objects to move?
• Why they prefer (move) to stay away from their “natural
state”
Galileo (1564-1642) B’day: 15th January
• “at rest” is a limiting case of the “natural state” of matter
which is in motion with uniform velocity
• Presence of external forces such as air resistance,
friction, and gravity keep the objects in motion
• Objects need an external force for motion
• When no force is acting (incl. air resistance, friction etc.)
objects move with constant (uniform) velocity
• His experiments are limited to horizontal surfaces ONLY
Newton’s Era (1643-1727)
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B’day 4th January
Generalized both Galileo’s and Aristotle’s
theories/observations and signed “in to the
law” of constitution of science. It states
“Objects at rest continues to be at rest, and
objects in motion continues to move with
uniform velocity along a straight line if and only
if the net force on the object is zero”
This is popularly known as Newton’s First Law
Motion when net Force is zero
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Objects can have two states when net
force is zero
• State of rest (static equilibrium)
• State of motion with zero acceleration
(dynamic equilibrium)
Examples
Trick Question
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We know from our daily life experience that an
external force is needed to move the object
Newton’s law suggests that objects in motion
continue to move with constant velocity
although net external force is zero!
What is wrong?
The law of inertia
•
If an accelerating car suddenly stops…why would the
driver run into windshield?
Chapter 5: Motion Along a Line
Static equilibrium
T1=100 N, T2=200 N, Find
direction and magnitude of T3
Dynamic equilibrium
Find T if angle of inclination is
20o
Speed of a car when exerted by
a Force
Difference between weight and
apparent weight
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The weight of an object is the force of
gravity on that object
If you are hanging from a rope, your
sensation of weight is due to the tension
force pulling up on you
If you measure your weight in an
elevator will it be the same as your
normal weight?
Measuring instruments for
weight
Apparent weight
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Weight of a person in a moving elevator
Friction