Speed Measures How Fast Position Changes Motion and

Speed Measures How Fast Position Changes Motion and Forces Unit Chapter 1 Section 2

I 1. Position can change at different rates. A measure DEFINITION: The rate at which distance changes compared to time Can be fast Can be slow SPEED Has a particular distance Faster speed covers more distance in same time

A 2. Calculating Speed �Requires both: distance and time �Formula is: s = d/t �S stands for: speed �D stands for: distance �T stands for: time

3. How does the unit of speed (m/s) relate to the formula for speed? �It shows a distance (meters) divided by a time (seconds). �Example: � 10 meters divided by 10 seconds = 1 m/s

B. Average Speed � 4. If someone ran 100 meters in 20 seconds, then ran another 100 meters in 25 seconds, what would the runner’s average speed be over the whole 200 meters? 100 m/20 s = 5 m/s 100 m/25 s = 4 m/s 4 m+5 m/2 s = 9 m/2 s= 4. 5 m/s OR: 200 meters/45 seconds = 4. 44 m/s

� 5. The distance – time graph shows the motion of a cat. During the 100 seconds shown, the cat was walking, running and resting. Label each line segment of the graph with a description of the cat’s motion. Explain your answers. Distance (meters) C. Distance – Time Graphs 80 70 60 50 40 30 20 10 0 Distance (meters) 0 20 40 60 80 100 Time (seconds)

II. Velocity Includes Speed and Direction 6. Need to know: SPEED and DIRECTION Changing either SPEED or DIRECTION causes a change in velocity VELOCITY Is considered a vector because it has both SIZE and DIRECTION Represented graphically by an ARROW

A-B. Velocity, Velocity vs. Speed � 7. Explain why velocity is a vector but speed is not. A vector has size and direction. Speed only has size. Velocity has size (SPEED) and direction. Therefore speed cannot be a vector.