Speed and Velocity 11.2

Speed A B C Speed: The ratio of the distance an object moves To the amount of time the object moves SI Unit of meters per second (m/s) Average Speed: Total distance divided by total time Example While traveling on vacation, you measure the times and distances traveled. You travel 35 kilometers in 0.4 hours, followed by 53 kilometers in 0.6 hour. What is your average speed? Instantaneous Speed: In this trip, did you go 88 km/hr the ENTIRE time? Your car’s speedometer measures instantaneous speed 88 km/h 35 km in 0.4 hrs 53 km in 0.6 hrs A B C

Graphing Motion A distance-time graph is a good way to describe motion Imagine you measure the distance a car went every other second Here’s what you record for car A: For car B: Can you see this: What would the STEEPNESS (slope) of these lines mean: The slope of a line on a distance-time-graph is SPEED Car A covers 100 meters every second 100 m/s Car B covers 100 meters every 2 seconds 100 m / 2s = 50 m/s

Graphing Varying Speed What does it seem this car is doing: He’s going fast from t = 0 s to t = 3 s He’s stopped from t = 3 s to t = 7 s He’s going slow from t = 7 s to t = 10 s How fast is he going? Fast = 200 m/s How slow is he going? Slow = 50 m/s

Velocity Caracas is about 200 km away from here You could get there in 2 hrs Speed? 100 km/h If you go 100 km/h, will you get to Caracas? You need a direction What was the difference between Distance Displacement One of them has a direction Same here: Speed Velocity Velocity = speed + direction

Combining Velocities Sometimes the motion of an object involves more than one velocity Like a boat in a fast moving river: If the river carries a current of 5 km/h East A boat with its motor set for 12 km/h East How fast does the boat look like it is going from the ground? Vector addition, X + Y = Z 17 km/h 5 km/h 12 km/h

Combining Velocities Sometimes the motion of an object involves more than one velocity Like a boat in a fast moving river: If the river carries a current of 5 km/h East A boat with its motor set for 12 km/h West How fast does the boat look like it is going from the ground? Vector addition, X + Y = Z 7 km/h 5 km/h 12 km/h

Combining Velocities Sometimes the motion of an object involves more than one velocity Like a boat in a fast moving river: If the river carries a current of 3 km/h East A boat with its motor set for 4 km/h North How fast does the boat look like it is going from the ground? Vector addition, X + Y = Z 5 km/h 3 km/h 4 km/h