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Speed and Velocity Chapter 9.2 Page 342 Objectives for 9.2 Know how to calculate the speed and average speed of an object. Know the difference between instantaneous speed and average speed Know how to describe an object’s velocity by stating the speed and direction. Know how to describe a change in velocity in terms of speed or direction or both. Know how to answer questions about speed and distance from a graph. Calculating Speed • Speed is defined as “the distance the object traveled in one unit of time”. • Speed= Distance Time • Example: If a car travels 180 km in 2 hours, then the car is traveling 90 km/h. 180 km 2h = 90 km h Constant Speed • If the speed of an object does not change, then it is traveling at a constant speed. – Ex: A boat traveling across the ocean. • If you know the distance an object travels in a given amount of time, you can use the formula for speed to determine the object’s constant speed. Speed= Distance Time Average Speed • Most objects do not move at constant speeds. • Example: When driving to Los Angeles, you may have to slow down for traffic, stop and get fuel, etc. • You can find an object’s average speed by dividing the total distance traveled by the total time. Average Speed= Total Distance Total Time • Example: A Cyclist travels 32 km during the first 2 hours and 13 km during the next hour. Total Distance: 32+13=45km Total Time= 2+1= 3 h Average Speed: 45km =15km/h 3h Speed The formula for calculating speed is: Speed = Distance Time Speed is defined as the rate at which an object travels OR the distance an object travels for a specific unit of time Common Expressions of Speed 45 miles per hour is the same as 45 miles or 45 mi/h hour 100 meters per second is the same as 100 meters or 100 m/s second Notice the Units!!!! miles hour = distance time = SPEED meters = second distance time = SPEED Calculating Speed Joe rides his bike a distance of 300 meters in 30 seconds. What is his speed? Distance = 300 meters Time = 30 seconds Speed = Distance = 300 meters = 10 m/s Time 30 seconds Calculating Speed 1. Jill can jog 2 miles in 0.5 hours. What is her speed? 2. A frog can jump 10 meters in 50 seconds. What is its speed? Instantaneous Speed • Instantaneous speed is the rate at which an object is traveling at a given instant in time When would it be important to know your instantaneous speed? Velocity • Velocity is a vector quantity. Vectors show both magnitude and direction. • Velocity= speed in a given direction • Therefore, if you know the velocity at which an object is moving, then you know the object’s speed, as well as its direction. • Example: A storm’s velocity is 25 km/h in an eastward direction. Graphing Speed Graphing Speed • You can use distance-versus-time graphs to interpret motion. Graphing Speed