Motion and Forces Unit Chapter 1 Section 2

I1. Position can change at different rates. Can be fast SPEED A measure Can be slow Has a particular distance Faster speed covers more distance in same time DEFINITION: The rate at which distance changes compared to time

A2. Calculating Speed Requires both: distance and time Formula is: s = d/t S stands for: speed D stands for: distance T stands for: time 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 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/20 s = 5 m/s 100 m/25 s = 4 m/s 4m+5m/2s = 9m/2 s= 4.5 m/s OR: 200 meters/45 seconds = 4.44 m/s

C. Distance – Time Graphs 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.

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

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