Chapter 9 Section 2 Speed & Velocity
What is physics? Physics is a description of our Universe Position is the foundation of physics. Our Universe is interesting because positions change.
Speed Speed (R) – Rate at which an object is moving. speed = distance / time R = d/t Like distance, speed does not depend on direction.
Speed A car drives 100 meters in 5 seconds. What is the car’s average speed? s = d/t s = (100 m) / (5 s) = 20 m/s 100 m 5 s 4 s 1 s 2 s 3 s
Speed A rocket is traveling at 10 km/s. How long does it take the rocket to travel 30 km?
Speed A racecar is traveling at 85.0 m/s. How far does the car travel in 30.0 s?
Average speed Speed is usually NOT CONSTANT Ex. Cars stop and go regularly Runners go slower uphill than downhill Average speed = total distance traveled/total time it took.
Average speed
Calculating 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 km Total Time: 1 h + 2 h = 3 hr Ave. Speed: total d/total t = 60 km/3 h = 20 km/h
Velocity Velocity (v) – speed with direction. velocity = displacement / time v = x / t
Pulling It All Together Back to our ant explorer! Distance traveled: 7 cm Displacement: +3 cm Average speed: (7 cm) / (5 s) = 1.4 cm/s Average velocity: (+3 cm) / (5 s) = +0.6 cm/s cm 1 2 3 4 5 6 7 8 9 10 + - 5 s 4 s 1 s 2 s 3 s
Question I travelled 25 km in 10 minutes. How many meters have I travelled? A) 25000 m B) .0112 m C) .025 m D) 2.5 m 25 km * 1000m/km = 25000 m
Question I ran 1000 m in 3 minutes. Then ran another 1000 m uphill in 7 minutes. What is my average speed? A) 100 m/min B) 2000 m/min C) 10 m/min D) 200 m/min E) 20 m/min Total Dist. = 1000 m + 1000 m = 2000 m Total Time = 3 min + 7 min = 10 min Ave speed = total dist/total time = 2000m/10 min = 200 m/min = D
Question What is the difference between speed and velocity? Speed is just distance/time. Velocity includes direction as well. Speed is just distance/time. Velocity includes direction as well.
Graphing Speed: Distance vs. Time Graphs Denver Phoenix
Graphing Speed: Distance vs. Time Graphs Speed = Slope = Rise/Run Rise
Graphing Speed: Distance vs. Time Graphs Speed = Slope = Rise/Run Rise=? 600 km 3 h
Graphing Speed: Distance vs. Time Graphs Speed = Slope = Rise/Run Rise=? 600 m 3 hr Rise/Run = 600 km/3 hr = 200 km/hr
Different Slopes Slope = Rise/Run = 0 km/1 hr = 0 km/hr Rise = 2 km Run = 1 hr Rise = 0 km Run = 1 hr Slope = Rise/Run = 2 km/1 hr = 2 km/hr Rise = 1 km Run = 1 hr Slope = Rise/Run = 1 km/1 hr = 1 km/hr
Average Speed = Total distance/Total time = 12 km/6 hr Question Below is a distance vs. time graph of my position during a race. What was my AVERAGE speed for the entire race? Average Speed = Total distance/Total time = 12 km/6 hr = 2 km/hr Rise = 12 km Run = 6 hr
Question What does the slope of a distance vs. time graph show you about the motion of an object? It tells you the SPEED