Average Speed and Acceleration Measuring motion Units for

Average Speed and Acceleration Measuring motion

Units for speed ¡ Depends, but will always be a distance unit / a time unit l l Ex. Cars: mi. /h Jets: km/h Snails: cm/s Falling objects: m/s

Calculating speed S = d/t Sound travels at a speed of 330 m/s. If lightning strikes the ground 1 km away from you, how long will it take for the sound to reach you? U: time K: s= 330 m/s d = 1 km ¡ P: S = d/t (units don’t match) 1 km = 1000 m

Calculating speed S = d/t Sound travels at a speed of 330 m/s. If lightning strikes the ground 1 km away from you, how long will it take for the sound to reach you? S: 330 m = 1000 m ¡ s t 330 m t = 1000 ms 330 m T = 3. 0 s

Average speed ¡ Speed is usually NOT CONSTANT l l ¡ Ex. Cars stop and go regularly Runners go slower uphill than downhill Average speed = total distance traveled/total time it took.

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. What is the average speed? U: average speed K: Total Distance: ¡ l 40 km + 20 km = 60 km = d Total Time: l P: 1 h + 2 h = 3 hr = t

Calculating Average Speed ¡

Question ¡ I travelled 25 km in 10 minutes. How many meters have I travelled? A) 25000 m B). 0112 m U: distance (m) K: Dist. = 25 km Time = 10 min P: 1 km = 1000 m S: 25 km 1000 m 1 m C). 025 m D) 2. 5 m = 25000 m

Question ¡ I ran 1000 m in 3 minutes. Then ran another 1000 m uphill in 7 minutes. What is my average speed? l l l A) 100 m/min B) 2000 m/min C) 10 m/min D) 200 m/min E) 20 m/min

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 U: lavg. speed B) 2000 m/min K: l Total Dist. = 1000 m + 1000 m = 2000 m C) 10 m/min Total Time = 3 min + 7 min = 10 min l D) 200 m/min l E) 20 m/min P: l

Question ¡ I ran 1000 m in 3 minutes. Then ran another 1000 m uphill in 7 minutes. What is my average speed? l l l A) 100 m/min B) 2000 m/min C) 10 m/min D) 200 m/min E) 20 m/min

Calculating Average Speed ¡ Classwork (due before you start lab)

Calculating Average Speed (graph) Distance (m) 120 100 80 60 40 20 0 1 2 3 Time (min) 4 5

Calculating Average Speed #1 1. What is the average speed after two minutes? U: average speed K: t = 2 mins d = 75 m P: S = total distance total time S: S = 75 m = 37. 5 m min 2 min

Calculating Average Speed #4 4. What is the average speed between two and four minutes? U: average speed between 2 -4 mins K: t = 2 mins d 2 mins = 75 m, d 4 min = 110 m P: s =total distance total time S: s = (110 m – 75 m) = 35 m = 17. 5 m 2 mins

Velocity ¡ Velocity – the SPEED and DIRECTION of an object. - displacement over time l Example: An airplane moving North at 500 mph ¡ A missile moving towards you at 200 m/s ¡

Velocity – speed in a given direction - displacement over time ¡ ex. go 10 miles to the party ¡ hurricane is moving 20 mph – so what if moving away from land ¡ Driving from here to California what would be your velocity? 65 mph W Velocity vs. speed

Question ¡ ¡ What is the difference between speed and velocity? Speed is just distance/time. Velocity includes direction as well.

Instantaneous Speed - speed at a point in time. Instantaneous speed is usually changing If not changing, then speed is ______. measured with a speedometer

Graphing Speed: Distance vs. Time Graphs Denver Phoenix

Distance-Time Graphs -Time on x-axis, position on y-axis

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 minutes Rise/Run = 600 km/3 hr = 200 km/hr

Different Slopes Slope = Rise/Run = 0 km/1 hr = 0 km/hr Rise = 2 km Rise = 0 km Run = 1 hr Rise = 1 km Run = 1 hr Slope = Rise/Run = 1 km/1 hr = 1 km/hr Run = 1 hr Slope = Rise/Run = 2 km/1 hr = 2 km/hr

Question Below= is a distance vs. time graph of km/6 hr Average ¡Speed Total distance/Total time = 12 my position =during a race. What was 2 km/hr my AVERAGE speed for the entire race? 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

Question ¡ Below is a distance vs. time graph for 3 runners. Who is the fastest? Leroy is the fastest. He completed the race in 3 hours

Acceleration ¡ ¡ Acceleration = speeding up Acceleration – the rate at which velocity changes l Can be an: Increase in speed ¡ Decrease in speed ¡ Change in direction ¡

Types of acceleration ¡ Increasing speed l ¡ Decreasing speed l ¡ Example: Car speeds up at green light screeeeech Example: Car slows down at stop light Changing Direction l Example: Car takes turn (can be at constant speed)

Question ¡ ¡ How can a car be accelerating if its speed is a constant 65 km/h? If it is changing directions it is accelerating

Calculating Acceleration ¡ If an object is moving in a straight line ¡ Units of acceleration: m/s 2 l m/s/s l

Calculating Acceleration What is the acceleration of a car that speeds up from rest (stopped) to 16 m/s in 4 sec? U: K: P: 0 s 0 m/s 1 s 4 m/s 2 s 8 m/s 3 s 12 m/s 4 s 16 m/s

Calculating Acceleration What is the acceleration of a car that speeds up from rest (stopped) to 16 m/s in 4 sec? 0 s 0 m/s 1 s 4 m/s 2 s 8 m/s 3 s 12 m/s 4 s 16 m/s

Question ¡ A skydiver accelerates from 20 m/s to 40 m/s in 2 seconds. What is the skydiver’s average acceleration? U: K: P:

Question ¡ A skydiver accelerates from 20 m/s to 40 m/s in 2 seconds. What is the skydiver’s average acceleration?

¡ http: //www. mot ortrend. com/fea tures/performan ce/1109_2011_ motor_trend_be st_drivers_car/

Graphing Acceleration ¡ Can use 2 kinds of graphs l l Speed vs. time Distance vs. time

Graphing Acceleration: Speed vs. Time Graphs 1)Speed is increasing with time = accelerating 2)Line is straight = acceleration is constant

Graphing Acceleration: Speed vs. Time Graphs Rise = 4 m/s Run = 2 s 1)In Speed vs. Time graphs: Acceleration = Rise/Run = 4 m/s ÷ 2 s = 2 m/s 2

Graphing Acceleration: Distance vs. Time Graphs 1)On Distance vs. Time graphs a curved line means the object is accelerating. 2)Curved line also means your speed is increasing. Remember slope = speed.

Question 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? 1) The car is slowing down 2) Acceleration = rise/run = -6 m/s ÷ 3 s = -2 m/s 2

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 1) be. Which slowing line downrepresents an object that is Remember: in distance vs. time graphs: accelerating? curved line = accelerating, flat line = constant speed

Question: Hard one Above is a graph showing the speed of a car over time. 1)What would a distance vs. time graph for this look like?

Momentum: The product of mass x velocity aka-the amount of umph a moving object has p=mv p=momentum m=mass What is the momentum of a 9 gram bullet traveling at 400 m/s? How fast would a 80 -kg man travel backwards if hit by a bullet with this momentum (assume the bullet does not go through his body)? Do people really fly backwards when they get shot like in the movies?

Momentum Transfer Examples -airbags -follow-through when throwing -bending knees when landing a jump