Transcript Chapter I: Concepts of Motion - Oklahoma State University

Announcements
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Midterm-I is on Thursday (Feb. 10th) between 5:30-6:30 pm.
Topics included are Chapters 1, 2, and 3
STUDY GUIDE is available in the course home page at
http://physics.okstate.edu/babu/2014
A formula sheet will provided to you during the test. For further
details see the study guide
Those who don’t have access to web can download the study
guide from library or can come by during the office hours to
pickup a copy
All HW solutions should be available on the web for you to
study them for the test
HW4: (Chapter 4): 4, 6, 9, 12, 28, and 34 (a, b, c) Due: Feb
18th.
There would not be regular class meeting on the exam day
(02/10/05) but, I will review the exam material. Those interested
may attend
Chapter 4 (contd.) : Newton’s
Laws
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In the light of various types of forces, we will
attempt to address the following questions
• What does a Force do? – A virtual experiment
• How does an object move when an external force
is applied?
• Are there additional relationships between Force
and motion? – Newton’s Laws
• What is the “natural state” of an object? – the
beginning of physics!
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Mass – definition of
Free body diagrams
What do forces do?
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Stretching of N rubber bands require a net force of NF
Effect of Force – A virtual
experiment
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Pull the block of mass
with different F values
and note down a
Plot F versus a
Observer that F is
proportional to a
Slope of the graph is a
constant
Observation: a  F
Does the acceleration depend
on the size of an object?
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Plot dependence of a for
different values of F
Observe that the slope of
the graph changes with
size of the object
If size of the object is
proportional to the matter it
contains, slope is inversely
proportional to the size of
the object
Loosely speaking, the size
of the matter is defined as
“mass” of the object
Mass  1/C and C  (a/F)
Stop to Think
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What do you mean by the size of the object?
What is the relationship between the slope of F
versus a graph?
Does the slope depend on the size of an
object?
Is there a better way of describing the size of
an object?
Is the shape of an object relevant?
Can we put both size and shape into a single
entity?
Newton’s Second Law
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An object of mass “m” subjected by a net
force F experiences an acceleration a in
the direction of the net Force F
~
a=
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F~n e t
m
Basic unit of Force is Newton and is denoted by N
1N = 1kg x 1m/s2
1lb weight = 4.45 N
Example
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Two forces (T1,T2) are
acting on an object of
mass “m”
The direction of net force
can be obtained by
applying the parallogram
theorem
Free body diagram (FBD)