MOTION Slide 2 Speed Slide 3 Distancetime graphs

MOTION Slide 2 Speed Slide 3 Distance/time graphs Slide 4 Speed Questions Slide 5 Acceleration Slide 6 Speed/time graphs Slide 8 Acceleration Questions

SPEED Speed is the distance that an object travels in a period of time. The standard units are meters Distance (m, km) and seconds (and therefore meters per second). However, sometimes km/hr is more t Time (s, hr) sensible. Meters per second = m/s v Speed (m/s, km/hr) s-1 means “divided by seconds” = m s d (a. k. a. velocity) =ms-1 A cyclist travels 25 km in ½ an hour. What is their speed - in kmhr-1 = 25 km/0. 5 hr = 50 km/hr - in ms-1 = 25000 m/1800 s = 13 m/s

DISTANCE/TIME GRAPHS A car takes 1. 5 minutes to travel 500 m down a busy road. It stops at lights for 30 seconds, then continues on for 1 minute as it goes another 1 km. Plot this on a distance/time graph. Using the distance/time graph: 1. 5 Distance (km) 1. What is the total distance traveled? = 1. 5 km 1 Steepest section is fastest 0. 5 2. 2. In what part of the trip = part 3 is the car going the fastest? 3. 3. What is the fastest v = Δd / Δt speed? v = 1 km/1 min v = 1000 m/60 s v = 16 Δd = 1 km Δt = 1 min 1 2 Time (min) 3 In a distance/time graph the slope of the line = the speed of the object.

SPEED QUESTIONS What would these look like on a distance/time graph? 1. stopped 2. slow 3. fast 4. accelerating Lab Manual pg 190/1

ACCELERATION Acceleration is the change in speed in an object in a period of time. change in Where do the units come from? Δv velocity (m/s) a=v t acceleration a = m/s s a Δt (m/s/s) a = m/s/s change in time (s) =m/s 2 = ms-2 It takes a cyclist 20 seconds to go from a standing start to 14 m/s. What is their acceleration? a = Δv/Δt a = 14 m/s / 20 s What is 14 m/s in km/hr? = 14 × 60 s × 60 min 1000 m a = 0. 7 ms-2 = 50. 4 km/hr

SPEED/TIME GRAPHS A runner travels at 4 m/s for 10 seconds, then stops suddenly for 5 seconds, then accelerates for 5 seconds to get to 8 m/s and continues for 10 seconds. In a speed/time graph the slope Plot this on a speed/time graph. of the line = the Speed 8 acceleration of Using the speed/time (m/s) the object. graph: 1. In what part of the trip is the runner going the fastest? 2. What is the acceleration in part 4? 4 = part 5 a = Δv/Δt a = 8 m/s/5 s a = 1. 6 ms-2 10 20 Time (sec) 30 In a speed/time graph the distance covered = the area under the graph.

SPEED/TIME GRAPHS Using the speed/time graph: 3. What distance is covered in part 1? d=v×t d = 4 m/s × 10 s d = 40 m Speed (m/s) 4. What is the total distance covered? 8 4 Part 1 = 40 m 10 Part 2 = 0 m Part 3 = 0 m Part 5 = v × t = 8 m/s × 10 s = 80 m Part 4 = v × t × = 8 m/s × 5 s × = 20 m Total =140 m = 40 + 80 + 20 20 Time (sec) 30

ACCELERATION QUESTIONS What would these look like on a speed/time graph? 1. stopped 2. slow 3. fast 4. accelerating Lab Manual pg 192/3, 212/3