Physics: It’s all around you…

1. Physics: It’s all around you… What is Physics?

2. What is Physics? • Physics is the science concerned with the fundamental laws of the universe. • Deals with: • Matter • Energy • Space • Time • And all of their interactions

4. Why take Physics? • You are continuing in science • You are interested in pursuing a career in the health sciences/medical sciences (nurse, doctor, kinesiology, pharmacist,…) • Engineering • Architect • Airline Pilot, Air traffic controller • Computer science • Space/astronomy • Optician/Optometry • Meteorology • Naval career • ….even careers such as firefighter, police (forensics),

5. But Wait…………. • We need to review your math skills  • Scientific notation • SI units • Significant Digits & Calculations • Error • We will be doing this over the next few days

6. Day 1: Scientific Notation • Extremely large and extremely small numbers are difficult to work with in common decimal notation • Scientific notation, or standard notation, expresses a number by writing it in the form: a x 10n

7. Scientific Notation copy Why? An easier way to write very large or very small numbers. In scientific notation, the number is expressed by: 1. writing the correct number of significant digits with one non-zero digit to the left of the decimal point 2. multiplying the number by the appropriate power (+ or – ) of 10

8. copy • Example: • 2394 = 2.394 x 1000 = 2.394 x 103 **large numbers have positive exponents 0.067 = 6.7 x 0.01 = 6.7 x 10 -2 **small numbers have negative exponents, Note: scientific notation also enables us to show the correct number of significant digits. As such, it may be necessary to use scientific notation in order to follow the rules for certainty (discussed later)

9. Using your calculator…. • On many calculators, scientific notation is entered using a special key; labelled EXP or EE. This key includes “x 10” from the scientific notation; you need to enter only the exponent. For example, to enter • 7.5 x 10 4 press 7.5 EXP 4 3.6 x 10-3 press 3.6 EXP +/- 3

10. Practice • Answers: • 6.8 x 103 • 5.3 x 10-5 • 3.9 x 1010 • 8.1 x 10-7 • 7.0 x 10-2 • 4.0 x 1011 • 8.0 x 10-1 • 6.8 x 101 • 1. Express each of the following in scientific notation (to 2 sig. dig.) • A) 6 807 • B) 0.000 053 • C) 39 379 280 000 • D) 0.000 000 813 • E) 0.070 40 • F) 400 000 000 000 • G) 0.80 • H) 68

11. Practice • Answers: • 70 • 5 200 • 8 300 000 000 • 0.101 • 6 386.8 • 0.004 086 • 630 • 0.035 0 • 2. Express each of the following in common notation • A) 7 x 101 • B) 5.2 x 103 • C) 8.3 x 109 • D) 10.1 x 10-2 • E) 6.3868 x 103 • F) 4.086 x 10-3 • G) 6.3 x 102 • H) 35.0 x 10-3

12. Investigation: Training on the Job Problem: How long (in hours) will it take the toy train to travel across Canada from east to west? Materials: • Metre stick -Small wind-up toy or hotwheels car - timer Procedure: • Measure as carefully as you can , in centimetres, how far the vehicle can travel in 5 seconds • Repeat step one two more times and then calculate the average. Observations:

13. Questions: How far (in cm) did the train travel in 1 second? How far (in km) did the train travel in 1 second? How many km would it travel in 1 hour? How long would it take (in days) to go across Canada from St. John’s in Newfoundland to Victoria in British Columbia? (highway distance) **7314 km**post your group’s answer to this question on the board Do you think it would make any difference if the vehicle travelled from west to east or east to west?

14. Extra Practice • Worksheet/homework

15. Day 2. SI Units

16. International System of Units (SI) Over hundreds of years, physicists (and other scientists) have developed traditional ways (or rules) of expressing their measurements. If we can’t trust the measurements, we can put no faith in reports of scientific research. As such, the International System of Units (SI) is used for scientific work throughout the world – everyone accepts and uses the same rules, and understands that there are limitations to the rules.

17. SI • SI Rules • In the SI system all physical quantities can be expressed as some combination of fundamental units, called base units. (i.e., mol, m, kg, …..) . For example: 1N = 1 kg•m/s2 => unit for force 1 J = 1 kg•m2/s2 => unit for energy

18. SI • SI Rules • The SI convention includes both quantity and unit symbols. • Note: these are symbols (e.g., 60 km/h) and are not abbreviations (e.g., mi./hr/) • When converting units, the method most commonly used is multiplying by conversion factors, which are memorized or referenced (e.g., 1 m = 100 cm, 1 h = 60 min = 3600 s) • It is also important to pay close attention to the units, which are converted by multiplying by a conversion factor (e.g., 1 m/s = 3.5 km/h)

19. SI (handout) Useful conversion factors!

20. SI Units copy It is easiest to keep track of your units if you use ratios/conversion factors to convert your units. Example problems: Convert 34.5 mm to m. Convert 23.6 mm to km. (HINT: You can avoid careless mistakes by first converting from mm into m, and then converting from m to km.) 3) Convert 5 km/h into m/s

21. SI Units Practice Convert 12.5 cm into mm An athlete completed a 5-km race in 19.5 min. Convert this time into hours. A train is travelling at 95 km/h. Convert 95 km/h into metres per second (m/s)

22. Investigation #2:Measuring Human Reaction Time With only a metre stick??!!??

23. Stopwatches - For a number of different applications it is necessary to know how quickly a person is able to react to some situation. - The first problem with trying to measure reaction time is that we must find a way to NOT have the reaction time of the measurer influence the measurement.

24. Yes we can!! • With only a common metre stick, a couple of friends, and some common items in the classroom it can be done. • By measuring the distance a metre stick falls before being caught, we can use a Physics formula to turn distance into time. • You likely haven’t seen this equation yet, but it is coming soon…

25. How does this work? • A couple of conditions are needed : • One assumption is that the metre stick is released, not thrown. • The second assumption is that gravity remains constant (with a value of 9.8 m/s2)

26. So what is this equation you ask? ∆t is the time in seconds, given the metre stick falls a distance ∆d metres. Be careful with your units, or you will get some strange values!

27. Your task • - Develop a simple procedure that clearly shows how you would conduct this investigation to minimize uncertainty • - Collect data for several trials for each member of your team. Record in a clear, meaningful manner. • - Convert your measured values into time values using the formula you just saw. • - Calculate the average reaction time for each member of the group, and then calculate the average reaction time for the whole group. • - Determine the percent difference between the shortest and longest reaction times in the group.

28. And what will be handed in? • - It is hoped that next day you will be able to exchange labs with another team who will evaluate your procedure. • - Their results and evaluation will be added to your lab as an appendix (their evaluation can be left as rough copy) • - Your lab will include Purpose, Apparatus (sketch), Procedure, Observations, Analysis (including percent difference calculations), Discussion (comments from the other team should help you here) and Conclusion and an STSE (relating science to technology, society, and the environment) example of the significance of reaction times • - For this lab, you will be submitting a single lab for the team but individual STSE examples (due on Monday)

29. Day 3. Uncertainty and Significant Digits

30. Uncertainty in Measurements: There are two types of quantities used in science: exact values and measurements. Exact values include defined quantities (1 m = 100cm) and counted values (5 beakers or 10 trials). Measurements, however, are not exact because there is always some uncertainty or error associated with every measurement. Because of this, there is an international agreement about the correct way to record measurements

31. Significant Digits The certainty of any measurement is communicated by the number of significant digits in the measurement. In a measured or calculated value, significant digits are the digits that are known for certain and include the last digit that is estimated or uncertain. There are a set of rules that can be used to determine whether or not a digit is significant (read pg. 650-651 of text)

32. Significant Digits (on handout) • Rules: • All non-zero digits are significant: 346.6 N has four significant digits • In a measurement with a decimal point, zeroes are placed before other digits are not significant: 0.0056 has two significant digits • Zeroes placed between other digits are always significant: 7003 has four significant digits • Zeroes placed after other digits behind a decimal are significant: 9.100 km and 802.0 kg each has four significant digits

33. Significant Digits (on handout) • In a calculation: • When adding or subtracting measured quantities, the final answer should have no more than one estimated digit (the answer should be rounded off to the least number of decimals in the original measurement) **number of decimal places matter • When multiplying or dividing, the final answer should have the same number of significant digits as the original measurement with the least number of significant digits ** significant digits matter • **when doing long calculations, record all of the digits until the final answer is determined, and then round off the answer to the correct number of significant digits(ADD TO HANDOUT)

34. Significant Digits Practice:

35. Significant digits

36. Precision Measurements also depend on the precision of the measuring instruments used – the amount of information that the instrument provides For example, 2.861 cm is more precise than 2.86 cm Precision is indicated by the number of decimal places in a measured or calculated value

37. Precision Rules for precision: All measured quantities are expressed as precisely as possible. All digits shown are significant with any error or uncertainty in the last digit. For example, in the measurement 87.64 cm, the uncertainty lies with the digit 4

38. Precision The precision of a measuring instrument depends on its degree of fineness and the size of the unit being used For example, a ruler calibrated in millimetres is more precise than a ruler calibrated in centimetres

39. Precision Any measurement that falls between the smallest divisions on the measurement instrument is an estimate. We should always try to read any instrument by estimating tenths of the smallest division.

40. Precision 4. The estimated digit is always shown when recording the measurement. Eg. The 7 in the measurement 6.7 cm would be the estimated digit

41. Precision 5. Should the object fall right on a division mark, the estimated digit would be 0.

42. Precision

46. worksheet

47. Reaction Time Lab – Step 2 • Today you are to have your PROCEDURE ready to be evaluated by another team. • When you get another team's procedure to evaluate you are to follow it PRECISELY to determine reaction times for each of the members of your team. • When you are completed, return the lab to the team along with ONE hand written page outlining your thoughts on their procedure and the results of your testing. (i.e. your teams reaction times.)

48. Day 4. Error

49. Error in Measurement Many people believe that all measurements are reliable (consistant over many trials), precise (to as many decimal places as possible), and accurate (representing the actual value). But there are many things that can go wrong when measuring. For example:

50. Error in Measurement There may be limitations that make the instrument or its use unreliable (inconsistent) The investigator may make a mistake or fail to follow the correct techniques when reading the measurement to the available precision (number of decimal places) The instrument may be faulty or inaccurate; a similar instrument may give different readings