3Measuring Distance Meter – international unit for measuring distance. 1 mm= 50 m
4We use the variable speed to describe how quickly something moves. Saying a race car, runner, or plane is “fast” is not enough to accurately describe its speed scientifically.
5The speed of a bicycle is the distance it travels divided by the time it takes.
6Constant means “does not change” so constant speed is speed that does not change. How do we know the speed of the bike is constant?
7Since speed is a ratio of distance over time, the units for speed are distance units over time units.
8An equation can be used to calculate speed, distance, or time if two of the three values are known.
9S = d/t Calculating Speed Speed (S) = distance traveled (d) / the amount of time it took (t).S = d/t
10Units for speedDepends, but will always be a distance unit / a time unitEx. Cars: mi./hJets: km/hSnails: cm/sFalling objects: m/s
11S = d/t Calculating speed If I travel 100 kilometers in 1 hour then I have a speed of…100 km/hIf I travel 1 meter in 1 second then I have a speed of….1 m/s
12The speed found by dividing the total distance by the total time is the average speed.
13Average speed Speed is usually NOT CONSTANT Ex. Cars stop and go regularlyRunners go slower uphill than downhillAverage speed = total distance_________________total time
14Calculating Average Speed It took me 1 hour to go 40 km on the highway. Then it took me 2 more hours to go 20 km using the streets.Total Distance:40 km + 20 km = 60 kmTotal Time:1 h + 2 h = 3 hrAve. Speed:total d/total t = 60 km/3 h = 20 km/h
15QuestionI jogged 100 m in 60 seconds. I then ran another 100 m uphill in 60 seconds. What is my average speed?A) 100 /minB) 2000 m/minC) 100 m/minD) 200 m/minE) 20 m/minTotal Dist. = 100 m m = 200 mTotal Time = 60 s + 60 s = 120 s = 2 minAve speed = total dist/total time =S = 200 m / 2 min = 100 m/ min
16How fast is a snake moving that can slither 20 meters in 5 seconds?
17It took Grandma 1.5 hours to drive 150 kilometers from her house to mine. How fast was she driving? It takes Brooke 20 minutes to run 100 meters. What is her speed in meters per minute?
18Velocity Velocity – SPEED with DIRECTION of an object. Example: An airplane moving North at 500 mphA missile moving towards you at 200 m/s
19Question What is the difference between speed and velocity? Speed is just distance/time. Velocity also includes direction.Speed is just distance/time. Velocity includes direction as well.
22Some practice1. Calculate the average speed of a car that travels 280 km in 4 hours.2. You ride your bicycle at an average speed of 15 km/h for 2 hours. How far did you go?3. How long will it take you to run 100 meters if you run at 5 m/s?
23More Practice...If a car drives 490 miles in 6 hours, how fast did it drive?If a rocket flies 17,000 miles per hour for 12 hours, how far will it go?If an airplane flies 800 miles at 300 miles per hour, how long will it take them to get there?
24In order to compare variables they must be in the same units. Comparing VariablesIn order to compare variables they must be in the same units.To convert between units, you multiply and/or divide by conversion factors.A conversion factor is an equivalent ratio.
25Using conversion factors Conversion factors are translators between one language of units and another.
26Velocity: Direction Matters Velocity is the speed of an object in a particular direction.Do not use velocity and speed in the same way because they are NOT the same thing!
27The difference between speed and velocity is DIRECTION!
28Velocity will always include a direction! The velocity of a plane headed to California might be 600 km/h west.The velocity of a train headed to New York might be 90 km/h north.
29Which are examples of velocity? m/s forward2. 1,500 km/hrm/s southcm/s downmph
30How to combine velocities If 2 velocities are going in the same direction, add them together.If 2 velocities are going in opposite directions, subtract the smaller from the larger. The resulting direction will continue to be that of the larger velocity.
31Velocity PracticeA car travels with a velocity of 20 m/s to the west. An insect inside the car flies with a velocity of 2 m/s to the east. What is the resultant velocity of the insect?Don’t forget, your answer must include a direction!!
32More Velocity Practice A bus is traveling forward at 30 km/h. You get up from your seat and walk toward the driver at a speed of 2 km/h.What is your resultant velocity?
33Velocity will change if: 1. The direction of travel changes:Example: A plane takes off to the east and then makes a turn to head north…it has changed velocity.2. The speed of travel changes:Example: The car slows down to leave the highway to go down an exit ramp.
34Graphing Speed: Distance vs. Time Graphs DenverPhoenix
35Graphing Speed: Distance vs. Time Graphs Speed = Slope = Rise/RunRise
36Graphing Speed: Distance vs. Time Graphs Speed = Slope = Rise/RunRise=?600 km3 hr
37Graphing Speed: Distance vs. Time Graphs Speed = Slope = Rise/RunRise=?600 km3 hrRise/Run = 600 km/3 hr= 200 km/hr
38QuestionWhat does the slope of a distance vs. time graph show you about the motion of an object?It tells you the SPEED
39QuestionBelow is a distance vs. time graph for 3 runners. Who is the fastest?Leroy is the fastest. He completed the race in 3 hours
40Acceleration Acceleration = speeding up Acceleration – the rate at which velocity changesCan be an:Increase in speedDecrease in speedChange in direction
41Types of acceleration Increasing speed Decreasing speed Example: Car speeds up at green lightDecreasing speedExample: Car slows down at stop lightChanging DirectionExample: Car takes turn (can be at constant speed)screeeeech
42QuestionHow can a car be accelerating if its speed is a constant 65 km/h?If it is changing directions it is accelerating
43Calculating Acceleration If an object is moving in a straight lineUnits of acceleration:m/s2
45QuestionA skydiver accelerates from 20 m/s to 40 m/s in 2 seconds. What is the skydiver’s average acceleration?
46Graphing Acceleration Can use 2 kinds of graphsSpeed vs. timeDistance vs. time
47Graphing Acceleration: Speed vs. Time Graphs Speed is increasing with time = acceleratingLine is straight = acceleration is constant
48Graphing Acceleration: Speed vs. Time Graphs Rise = 4 m/sRun = 2 sIn Speed vs. Time graphs:Acceleration = Rise/Run= 4 m/s ÷ 2 s = 2 m/s2
49Graphing Acceleration: Distance vs. Time Graphs On Distance vs. Time graphs a curved line means the object is accelerating.Curved line also means your speed is increasing. Remember slope = speed.
50Question Run = 3 s Rise = -6 m/s Above is a graph showing the speed of a car over time.1) How is the speed of the car changing (speeding up,Slowing down, or staying the same)?2) What is this car’s acceleration?The car is slowing downAcceleration = rise/run = -6m/s ÷3s = -2 m/s2
51curved line = accelerating, flat line = constant speed Question:The black and red lines represent a objects that are accelerating. Black is going a greater distance each second, so it must be speeding up. Red is going less each second, so must be slowing downRemember: in distance vs. time graphs:curved line = accelerating, flat line = constant speedWhich line represents an object that is accelerating?