1. Physics – Measures and Metrics
Cpt. 2

2. 2.1 Space and Time
Space in physics means the three dimensions of up-down, left-right, and front-back.
The three dimensions of space are described with length units, such as meters, inches, and feet.
Time provides another dimension for describing when something occurs.

3. 2.1 Thinking about Distance
Measurement
is a quantity and a unit
Distance
is the amount of space between two points
is measured in units of length

4. 2.1 Two Common Systems of Units
Science problem solving requires both:
Metric or S.I. system
English system

5. 2.1 Two common systems of length
Almost all fields of science use metric units.
They make calculations easier because the units are based on factors of ten.

6. 2.1 Converting from one unit to another
It is often necessary to take a measurement in one unit and convert it into a different unit using conversion factors.

7. Converting length in yards to meters
A football field is 100 yards long. What is this distance expressed in meters?
You are asked for the distance in meters (m).
You are given the distance in yards (yds).
Relationship: 1 yard= 3 feet
100 yds x 3 ft x m = m
1 yd 1 ft

8. 2.1 Time Two ways to think about time: What time is it?
11:52 a.m. on March 12, 2010
How much time has passed?
2 hr: 22 min: 42 sec.
A quantity of time is often called a time interval.

9. 2.1 How is time measured?

10. Converting a mixed time to seconds
How many seconds are in 1 hour, 26 minutes, and seconds?
You are asked for time in seconds.
You are given a time interval in mixed units.
1 hour = 3,600 sec minute = 60 sec
Do the conversion:
1 hour = 3,600 sec
26 minutes = 26 × 60 = 1,560 sec
Add all the seconds:
t = 3, , = 5, sec

11. 2.1 Time scales in physics
Events in the universe happen over a huge range of time intervals.
In many experiments, you will be observing how things change with time.

12. Significant Figures
Term used to describe the digits in a measurement that are known with confidence plus one that is estimated.
Measurements are made to the limits of the instrument used.
All measurements contain some uncertainty.

13. Rules for Counting Sig. Fig.
In any measurement:
All nonzero digits count.
Zeros between digits count.
Initial zeros never count.
Final zeros count IF there is a decimal present.

14. Practice counting significant figuresm
30474 mm
0.25 ml km
1.00 kg
50 °C kJ

15. Math with Sig. Fig. For addition and subtraction: (not too common)
Line up the decimal pts.
Do the math.
Round the answer to the least accurate place value.
Don’t forget the units !!!

16. Math with Sig. Fig. For multiplication and division: 1) Do the math
2) Count the # of sig figs in each of the components.
3) Round the answer to the least number of digits.
4) Don’t forget the units!

17. 2.2 Mass, matter, and atoms Mass Two effects mass has on matter:
is the amount of “stuff” an object contains. (Kg)
Two effects mass has on matter:
Weight
is the force of the Earth’s gravity pulling down.
Gravity acts on an object’s mass.
Inertia
is the tendency of an object to resist changes in motion.
Inertia comes from mass.

18. 2.2 Measuring mass Kilogram
is the mass of 1 liter of water or 1,000 cubic centimeters of water.

19. 2.2 Very large and very small numbers
Because physics covers such a wide range of values for length, time, and mass you will need a method of working with large and small numbers.
In scientific notation, numbers are written as a value between 1 and 10, multiplied by a power of 10 called the exponent.

21. 2.2 Matter and atoms A single atom is about 10-10 meters in diameter.
Aluminum foil is thin but still more than 200,000 atoms thick.
Whether matter is a solid, liquid, or gas depends on how the atoms are organized.

22. 2.3 Experiments and Data
Data are the measurements and calculations that you make during the experiment.
Things you measure in experiments are fundamental quantities.
Derived quantities can (sometimes) be measured, but are often calculated from things you originally measured.

23. 2.3 Speed
Speed
is a derived quantity calculated from measurements of distance and time.
Other derived quantities include frequency, density, acceleration, intensity, and energy.
Each of these units can be broken down into combinations of the fundamental units of length, mass, and time.

24. 2.3 Area and volume A solid object has surface area as well as volume.
is the measurement of the extent of an object’s surface or area without including its thickness.

25. 2.3 Area and volume
Volume
is a measure of the space occupied by an object.

26. 2.3 Density
Density describes how much mass is in a given volume of a material.
The units of density are mass divided by volume.
Identically-sized cubes of iron, polyethylene, and glass contain different amount of mass.

27. 2.3 Density
Solids range in density from cork, with a density of 120 kg/m3, to platinum, a precious metal with a density of 21,500 kg/m3.

28. 2.3 Accuracy and precision
is the quality of being exact and free from error.
is how close a measurement is to the true (accepted) value.
Precision
means how small a difference a measurement can show.

29. 2.3 Variables and relationships
Factors that affect the results of an experiment are called variables.
The science of physics can be thought of as “the search for the relationships between all the variables that describe everything.” …..Wow…..
To learn about something specific in nature, scientists instead select a small set of related variables and define it as a system.

30. 2.3 Variables for a car on a ramp

31. 2.3 Experimental design
We do experiments to find out what happens when we change a variable.
The variable that is changed is called the experimental variable.
The variables that are kept the same are called the control variables.
When you change one variable and control all of the others, we call it a controlled experiment.
Controlled experiments are the best way to get reliable data.

32. 2.3 Experimental design
The procedure is a collection of all the techniques you use to do an experiment.
Your experimental technique is how you actually do the experiment.
Each repetition of the experiment is called a trial.

33. 2.3 Graphical data A graph shows how two variables are related.
By convention, graphs are drawn a certain way.
The dependent variable goes on the y-axis which is vertical.
The independent variable goes on the horizontal or x-axis.

34. 2.3 Graphical models
A graph is a form of a mathematical model because it shows the connection between two variables.
A graphical model uses a graph to make predictions based on the relationship between the variables on the x- and y-axes.

35. 2.3 How to make a graph Decide what to put on the x and y axes.
Make a scale and label the axes by counting boxes to fit your largest value (multiples of 1, 2, 5 or 10 are best).
Plot your points.
Draw a best fit curve.
Create a title and label
each axis.

37. 2.3 Recognizing relationships in data
When there is a relationship between the variables, a graph shows a clear pattern.

38. 2.3 Recognizing relationships in data
You can tell how strong the relationship is from the pattern.
If the relationship is weak, even a big change in one variable has little effect on the other.

39. 2.3 Recognizing relationships in data
Inverse Relationship
When one variable increases and the other decreases, it is an inverse relationship.
Graphs of inverse relationships often slope down to the right. (will be curved)
Pressure
Volume