What is Physics

1
What is Physics??

• The science of matter and energy and of
  interactions between the two.
• Physics is concerned with the description of
  nature the description and explanation of
  natural phenomena in our physical world.
• IOW physics is concerned with how and why
  things work or behave the way they do!!

2
The Universe (or Nature) consists of

• Matter, Energy, Space, and Time

3
How do we describe nature??

• Four Fundamental Quantities from which all other
  quantities are derived
• LENGTH
• MASS
• TIME
• ELECTRIC CHARGE (next semester!)

4
Units of Measure are used to describe these
fundamental quantities

• There are different Systems or Conventions to
  flesh out these units of measure
• The most commonly used one in Science is the
  Systeme Internationale (SI)
• It is also known as the mks system

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SI Units
1 kilogram weighs 2.2 pounds
1 meter is 3.3 feet long
1 second is 1 second in any unit system
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Unit Prefixes
Kilo (k) means multiply by 1000 1 kilogram (kg)
103 1000 grams (g) Centi (c) means divide by
100 1 centimeter (cm) 10-2 0.01 meter
(m) Milli (m) means divide by 1000 1 millimeter
(mm) 103 0.001 meter (m)
Other prefixes may be found on page 3 in your
book.
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Example
Units behave like algebraic quantities. When
identical units are divided, they cancel out.
Convert 65 miles/hour to kilometers/hour
Angel Falls in Venezuela has a total drop of 979
m. Convert to feet
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Significant Figures

• The number of digits whose values are know with
  certainty.
• 5.5 feet 2 s.f.
• 5.50 feet 3 s.f.
• 1500 feet 2 s.f.
• 1.500 x 103 4 s.f.

9
Group Problem Solving
How many seconds are there in one day? Find out
by converting 1 day into seconds, by canceling
units.
10
Review of Trigonometry
SOHCAHTOA
H
O
?
A
For right triangles only!
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Example
SOHCAHTOA
H
O
?
A
12
Inverse Trig. Functions
H
O
?
A
SOHCAHTOA
13
Example
SOHCAHTOA
H
O
?
A
14
Pythagorean Theorem
H
O
?
A
H2 A2 O2
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Example
SOHCAHTOA
H
O
?
A
16
Group Problem Solving
The peak of Mt. Fuji in Japan is 12,400 ft high.
A person, several miles away, notes that the
angle between the level ground and the peak is
30o. Find the distance (in feet) from the person
to the point on the level ground directly beneath
the peak.
17
Scalars and Vectors
Vocabulary Scalars are numbers Examples 10
meters 75 kilometers/hour Vectors are
numbers with a direction Example 10 meters to
the right 75 kilometers/hour north
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Scalars and Vectors
Scalar 25 meters Vector 25 meters north
Scalar 25 meters Vector 25 meters east
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Adding Vectors
To add two vectors, A B A B 1. place the
head of one vector on the tail of the other
vector B A 2. draw a new vector from
the tail of the first to the head of the
second B A C
3. This new vector is is called the
resultant A B C
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Subtracting Vectors
To subtract two vectors, A - B A
B 1. Multiply vector B by -1 A
(-B) A -B 2. Then simply
add A and -B, head to tail. -B
A C 3. A -B C
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The Components of a Vector
P
A x y We call x and y the components of
the vector A.
A y x
O
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Addition of Vectors(using Components)
A B C Add the x components of A and B to
each other to get the x component of C. Then,
add the y components of A and B to each other to
get the y component of C.
C B A
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Use Fig 1.20 from book herePage 13
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Example
You travel 2 km due East on 26th street, then
turn right on Main street and head Southeast for
1 km, what are the components of your
displacement?
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Example
B By Bx
If B has a magnitude of 25 kilometers in a
direction 30 degrees North of East, what is the x
component of B?
?30o
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Group Problem Solving
If A has a magnitude of 10 meters, and is
pointing 45 degrees South of East, what is the
magnitude (length) of the vector Ay?
Ax
?
Ay
A