welcome to regents physics! mrs. patterson course introduction
TRANSCRIPT
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Welcome to Regents Physics!
Mrs. Patterson
Course Introduction
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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.
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What will we investigate?
There are 5 basic units in physics:
-Mechanics
-Energy and Work
-Electricity and Magnetism
-Waves
-Modern Physics
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Success Skills
• Conceptual (Why does this happen?)
• Problem Solving
• Data Analysis
• Lab design and Reporting
• Self-guidance
• Observation
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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.
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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).
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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!
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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)
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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.
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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?
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Factor-Label method
a.k.a Dimensional Analysis
• FLM is a technique used to convert from one unit to another using appropriate conversion factors.
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Let’s do it!
Let’s convert 100 km/hr to m/s.
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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.
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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
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The Four Sig Fig Rules:
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Rule #1: Non-zero digits are always significant.
• Example:
How many sig figs in 2.735 m?
• Answer:
Four sig figs
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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
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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
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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
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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 ____
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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 = ________
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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 = _______
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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
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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. ________________
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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.
____________________
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“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.
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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:
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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”.