What is Physics??

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# What is Physics?? - PowerPoint PPT Presentation

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.

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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!!

### The Universe (or Nature) consists of…

Matter, Energy, Space, and Time

How do we describe nature??
• Four Fundamental Quantities from which all other quantities are derived
• LENGTH
• MASS
• TIME
• ELECTRIC CHARGE (next semester!)

### 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

SI Units

1 kilogram weighs

2.2 pounds

1 meter is

3.3 feet long

1 second is 1 second in any unit system

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) = 10–3 = 0.001 meter (m)

Other prefixes may be found on page 3 in your book.

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:

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.
Group Problem Solving

How many seconds are there in one day? Find out by converting 1 day into seconds, by canceling units.

Review of Trigonometry

SOHCAHTOA

H

O

A

For right triangles only!

Example

SOHCAHTOA

H

O

A

Example

SOHCAHTOA

H

O

A

Pythagorean Theorem

H

O

A

H2 = A2 + O2

Example

SOHCAHTOA

H

O

A

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.

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

Scalars and Vectors

Scalar: 25 meters

Vector: 25 meters north

Scalar: 25 meters

Vector: 25 meters east

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

AC

3. This new vector is

is called theresultant

A+ B= C

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,

-B

A

C

3. A + -B = C

The Components of a Vector

P

A = x + y

We call x and y the

components of the vector A.

A

y

x

O

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 ofAand B to each other to get the y component of C.

C B

A

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?

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

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