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 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
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
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
Conversion Factors we use : 1 meter = 100 centimeters 1 meter = 1000 millimeters 1 kilometer = 1000 meters Interchange meter for, seconds, grams, Newtons, Joules…
Time conversions 1 minute = 60 seconds 1 hour = 60 minutes 1 day = 24 hours 1 year = 365 days (approximation)
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
Mathematically: 1.85 m x 100 cm = 185 cm 1 m
Example, you try: Convert 645 seconds into the same number of minutes
Answer Since we are converting to a larger unit, we divide by factor 645 sec / 60 = 10.75 min
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
Try these 456.3 mm (millimeters) = _____ m 456.3 /1000 = .4563 m 8 days = ______ min 8 x (24) x (60) = 11520 min
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
Average velocity Displacement / time Units are m/s V = d / t
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
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
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
Manipulating equations V = d / t Vt = dt / t t’s cancel on right Vt = d same as d = vt
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
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
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
Due Monday Homework Handout #1 You should get a copy from me in class There is a copy on website
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)