Welcome to Regents Physics!

Mrs. Patterson

Course Introduction

What is Physics?

Physics is the study of the physical or natural world.

• It is the most basic science…

The study of motion, forces, energy, matter, heat, sound, light, waves, and the composition of matter.

What will we investigate?

There are 5 basic units in physics:

-Mechanics

-Energy and Work

-Electricity and Magnetism

-Waves

-Modern Physics

Success Skills

• Conceptual (Why does this happen?)

• Problem Solving

• Data Analysis

• Lab design and Reporting

• Self-guidance

• Observation

SI (System International)

Base Units:

Fundamental units (also called base units)• Length = meter (m)

• Mass = kilogram (kg)

• Time = seconds (s)

A base unit is independent of other units.

Derived Units:

Derived Units are combinations of fundamental units.

Examples:

• Meters per second (m/s) used to measure _______?

• Kilogram * meter squared per second (kg*m2/s) is used to measure energy (the joule).

Common Prefixes

Look at your reference tables – front page, bottom left corner, “Prefixes for Powers of 10”

Example:

1 ns = 1 x 10-9 s

1 nm = 1 x 10-9 m

• We can make conversion factors!

Practice:

How many seconds are in 1 picosecond?

Answer: 1 ps = 1 x 10-12 s

What if we turn the question around?

• How many picoseconds are in one second?

Answer: (1 ps/ 1x10-12s) = (1x1012ps/s)

Getting Conversion Factors from Prefix Table

• We often need to change from one unit to another… we can do this using conversion factors.

• Here’s the key…Units are treated as mathematical factors, and can be divided out.

Let’s do it!

Let’s convert 365 meters to km. ________

Why can’t I just move the decimal place?

• You can, but only if you are going from one metric unit to another.

• What if you need to convert a derived unit, like km/hr to m/s?

Factor-Label method

a.k.a Dimensional Analysis

• FLM is a technique used to convert from one unit to another using appropriate conversion factors.

Let’s do it!

Let’s convert 100 km/hr to m/s.

Precision

Precision is the degree of exactness to which the measurement of a quantity can be reproduced.

Precision is linked to significant figures:

• Significant figures includes all known digits plus one estimated digit.

Accuracy

Accuracy is the extent to which a measured value agrees with the standard or accepted value.

Accuracy is measured using percent error.% error = measured value – accepted value x 100

accepted value

precision and accuracy

The Four Sig Fig Rules:

Rule #1: Non-zero digits are always significant.

• Example:

How many sig figs in 2.735 m?

• Answer:

Four sig figs

Rule #2: Zeros between two other significant digits are significant.

• Example:

How many sig figs in the value 202.03 kg?

• Answer:

5 sig figs

Rule #3: All final zeros after the decimal point are significant.

• Examples:

- 0.002 kg has one sig fig

- 0.020 kg has two sig figs

- 0.200 kg has three sig figs

Rule #4: Zeros used solely for spacing the decimal point are not significant (unless a decimal point is present)

• Examples:

- 63400 s has 3 sig figs

- 63400. has 5 sig figs

Try these examples:

1) 47.90 _____ 6) 50.0 ____

2) 235.45 _____ 7) 0.0204 ____

3) 1000 _____ 8) 1.30000 ____

4) 0.0008 _____ 9) 12.004 ____

5) 70. _____ 10) 500.009 ____

Adding and Subtracting with Significant Figures

The Rule: Perform the operation, then round off to the least precise value involved.

Examples: 412.57 + 35 = ________

23.941 – 12.79 = ________

1309.75 – 1000 = ________

Multiplying and Dividing with Significant Figures

The Rule: Perform the operation, then round off the answer to the same number of significant figures and the factor with the fewest sig figs.Examples: 24.0 x 30.00 = _______

45.79/2 = _______ 100./4.0 = _______

100./3 = _______ 7652 x .0040 = _______

Scientific Notation

Numbers expressed as: M x 10n

Where:

•”M” is the “mantissa”, a number between 1 and 10. The mantissa must contain the correct number of sig figs.

• “n” is the exponent, an integer

Let’s Practice• Express 0.0000578 in scientific notation. ________________

• Express 2900 in scientific notation.

________________

• Express 5.409 x 107 as an integer.

_______________

• Express 8.92 x 10-5 as an integer. ________________

One more thing…

Use your calculator to perform the following calculation:

(3.45 x 1012kg) x (4.3 x 10-2 m/s)

Express your answer with the correct number of significant figures, and with the correct units.

____________________

“Order of Magnitude”

• “Order of Magnitude” is the power of 10 closest to a numerical quantity’s actual value. Powers video powers demo

Examples: powers demo

1693 kg has an order of magnitude of 103 kg.

8534 kg has an order of magnitude of 104 kg.

Estimating

Some questions will pop up from time to time such as: How tall is a door? Or how thick is a piece of paper? The choices will force you to put all answers in one unit that makes sense. Let’s practice:

How tall is a physics student?

a. 1 x 10-2 km c. 1 x 102 m

b. 1 x 102 cm d. 1 x 104 mm

The answer is “b”. This may seem a little strange, but we are estimating here. If we put all the answers into meters, we see choice “a” is 10 m, “b” is 1 m, “c” is 100 m, and “d” is 10 m. Although most students are closer to 2 m, the only logical choice is “b”.