1. Measuring Motion Chapter 11

2. What is Motion? Motion is changing position along a certain path. In the first part of physical science, we have 2 goals: To understand how things move (kinematics) To understand why things move (dynamics)

3. How do things move? Vocabulary Frame of reference Distance Displacement Speed Velocity Slope Acceleration Gravity As we go through the section, create flashcards for these words.

4. Frame of Reference A reference point is a starting point… a place that everyone calls zero. When everyone knows where 0 is, then it is much easier to describe the location or position of objects. Example: In races, the starting line is 0, or your reference point. Everything is measured from the starting line.

5. Distance vs. Displacement Distance is the total path an object travels. Measures how far an object moves along a path. Displacement is the line from the beginning to the end. Measures how far between the starting point and ending point. Start End

6. Distance vs. Displacement You start at your house (0). You go to the store. Then you go to your friend’s house. What is the distance that you travel? 8 houses What is your displacement from the beginning to the end? 2 houses 0 store friend

7. Speed vs. Velocity Speed describes how fast an object is moving. Velocity is an object’s speed in a particular direction. Ex. Does your car’s speedometer read speed or velocity? Speed What could make this a velocity? If your car also has a compass in it.

8. Variables Time is shown as a little t. “t” is measured in seconds, usually. Sometimes minutes or hours Distance is shown as a little d or a little x. “d” or “x” both mean the same thing. Usually measured in meters Sometimes kilometers, miles, feet, or inches Velocity & speed are shown as little v. “v” is usually measured in m/s Sometimes mph, km/hr, ft/s

9. Finding speed and velocity To calculate speed, you need to know 2 things Distance that an object traveled (in meters) Time it took to travel that distance (in seconds) Speed = distance  time Or Units for speed and velocity: m/s or km/hr or miles/hour

10. Calculating Examples: Find the speed of a runner who runs 120m, south in 2 minutes. d = 120mt = 2 min = 120s v = 120m  120s = 1m/s For velocity, we need to specify direction. 1m/s, SOUTH Find the distance a horse travels, who is galloping at 15m/s for 90 seconds. V = 15 m/st = 90s 15m/s = d  90s d = 15m/s x 90s d = 1350m

11. Problems for you p. 369: practice problems: #1-3

12. Graphing Motion To investigate the relationship between distance and time, you can use Mathematical equations or Graphs of distance vs. time Distance (m) Time (s)

13. Here is an example of a distance vs. time graph. What can it tell us? Where the object was at any time. How long it took the object to travel a certain distance. The speed of the object. = SLOPE

14. What is slope? In math, to find slope, you have to Pick 2 points A = (5s, 15m) B = (15s, 45m) Calculate rise Change in y = rise 45m -15m = 30m Calculate run Change in x = run 15s – 5s = 10s Slope = rise  run 30m  10s = 3m/s A B Definition: How steep a line is

15. What does the slope mean? The slope of a distance vs. time graph gives us the velocity. For the object graphed below, the velocity is 3m/s in the positive direction.

16. Direction from a graph Line A is in the positive direction, because x is steadily increasing as time increases. Line C is in the negative direction, because x is steadily decreasing as time increases. What direction is the object in line B going? Positive direction A B C

17. What else does this graph tell us? It tells us Starting position of each object Ending position of each object Speed and direction of each object Which object is going faster or fastest A B C

18. What else does this graph tell us? What is B’s speed? 1.33m/s Who is going faster, A or B? A How could we tell that without doing the math? because the line of B is not as steep as A’s line A B C

19. What does a flat horizontal line mean? Time Increasing Distance Staying the same Speed None. The object is not moving Distance (m) Time (s)