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Friday

Friday. What are we going to do?. Record data for 2 runs more than minimum block length Conversions Homework! Review Homework Handout #1 Motion Detectors. Main point. How to accurately describe the motion of objects. MPV’s.

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Friday

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  1. Friday

  2. What are we going to do? • Record data for 2 runs more than minimum block length • Conversions • Homework! • Review • Homework Handout #1 • Motion Detectors

  3. Main point • How to accurately describe the motion of objects

  4. MPV’s • I will be recording data to see who has moved their car past the minimum distance twice • Get your papers out, complete all calculations • Task two job

  5. Task 2 (Due Wednesday) • The results must by typed or printed on an index card (3x5 or 4x6) in a table that includes: • For each run: overall displacement/ distance/ time/ velocity • The correct unit value for each number • The mean of the 3 velocity times • Discuss at least 2 specific reasons why the values may not be absolutely correct (sources of error) A drawing or photo of the car used to gather evidence is to be attached to the other side of the index card

  6. Conversions • If you are converting to a smaller unit, multiply the measurement to get a bigger number. • If you are converting to a larger unit, divide the measurement to get a smaller number

  7. Conversion Factors we use : • 1 meter = 100 centimeters • 1 meter = 1000 millimeters • 1 kilometer = 1000 meters • Interchange meter for, seconds, grams, Newtons, Joules…

  8. Time conversions • 1 minute = 60 seconds • 1 hour = 60 minutes • 1 day = 24 hours • 1 year = 365 days (approximation)

  9. Example problem • Convert 1.85 meters into centimeters • Since meters are larger than centimeters, we are converting to a smaller unit • We multiply 1.85 by the converting factor (100) = 185 cm

  10. Mathematically: • 1.85 m x 100 cm = 185 cm 1 m

  11. Example, you try: • Convert 645 seconds into the same number of minutes

  12. Answer • Since we are converting to a larger unit, we divide by factor • 645 sec / 60 = 10.75 min

  13. Another way to do the solution • Dividing is the same as multiplying by the inverse • 645 / 60 = 645 x 1/60 • 645 sec x 1 min/ 60 sec = 10.75 min

  14. Try these • 456.3 mm (millimeters) = _____ m • 456.3 /1000 = .4563 m • 8 days = ______ min • 8 x (24) x (60) = 11520 min

  15. Page 17 • Write 550 millimeters as meters • Convert to bigger, divide • 550/1000 = .550 m • Write 3.5 seconds as milliseconds • Convert to smaller, multiply • 3.5 x 1000 = 3500 millseconds

  16. Average velocity • Displacement / time • Units are m/s • V = d / t

  17. Book Problems • Find the velocity in m/s of a swimmer who swims 110 m toward the shore in 72 s • Answer v = d/t = 110 m/ 72 s = 1.5 m/s

  18. Problem 2 • Find the velocity in m/s of a baseball thrown 38 m from third base to first base in 1.7s. • Answer v = d/t = 38 / 1.7 = 22 m/s

  19. Problem 3 • Calculate the displacement in meters a cyclist would travel in 5.00 h at an average velocity of 12.0 km/h to the southwest. • Answer: • Rearrange equation v = d/t to d = vt • D = vt = 12.0 km/h x 5.00 h = 60 km • Convert 60 km into meters • Convert to smaller units means multiply • 60 km (1000 m/1 km) = 60,000 m

  20. Manipulating equations • V = d / t • Vt = dt / t t’s cancel on right • Vt = d same as d = vt

  21. Ex: problems • A) How long will it take you to travel a length 307 m at 6.4 m/s? • Ans: v = d/t 6.4 = 307 /t t =307/6.4 = 48s • If a car travels 150 blocks in 34.3 seconds, what is it’s average velocity in m/s. • Ans: convert blocks to meters- 150 x .305 = 45.8m • Then calc. vel. 45.8m /34.3s = 1.34 m/s

  22. Try this • If you can go 30 meters in 2.0 second, what is your average velocity in m/s? • Answer: 30/2 = 15 m/s • What is your average velocity in km/h? • Ans: to convert to km, you divide 30 by 1000 = .03 • to convert to hours, you divide 2 by 3600 = .000555 • Divide .03/ .000555 = 54.05

  23. Or • To convert from m/s to km/h multiply by 3.6 • To convert from km/h to m/s divide by 3.6

  24. Due Monday • Homework Handout #1 • You should get a copy from me in class • There is a copy on website

  25. Motion Detectors • Gather much more information on motion during any given time period • Uses sound to measure position • Produces a visual report on motion information ( A graph)

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