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Honors Physics (Power Point #2

Honors Physics (Power Point #2. Instantaneous and Average Speed. Motion Map. Soon, you will be walking toward and away from the motion probe and creating graphs when you do so. Distance vs Displacement.

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Honors Physics (Power Point #2

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  1. Honors Physics (Power Point #2 Instantaneous and Average Speed

  2. Motion Map • Soon, you will be walking toward and away from the motion probe and creating graphs when you do so.

  3. Distance vs Displacement • Distance- A running total of how far you traveled in any direction. (Think of a pedometer attached to your body and you count your steps). • Displacement- It is a vector quantity. It is precisely defined as how far in a particular direction an object is from the starting point.

  4. A representation of the difference

  5. Speed vs Velocity • Speed- how fast you are moving. This is known as a scalar quantity. • Velocity- how fast you are going with a direction attached.

  6. Example 1: • An out-of shape runner runs 10 times around a quarter-mile track in 30 minutes? He ends up where he starts. • (a) What is the runner’s velocity? (in miles/hour) • (b) What is the runner’s speed? (in miles/hour)

  7. It the speed average or instant? • Average Speed- It is the total distance traveled per unit time • Instantaneous Speed-As the time interval shrinks down, the rate of speed can be precisely determined for that moment in time.

  8. Example 2: • Mr. Boyle travels 3 miles to work each morning. He travels 1.0 mile at 25 miles/hour, 1.0 mile at 40 miles/hour, and 1.0 mile at 5 miles/hour. He also stops at 3 traffic lights for a total of 2.0 minutes. • (a) How long does he take to complete his journey? • (b) What is his average speed?

  9. A graphical representation of motion • For any position-time graph, we can determine the average speed by drawing a straight line between any two points on the graph. • If the speed is constant, the graph of position vs. time is a straight line. The slope indicates the velocity. Object 1-positive slope, positive speed Object 2- zero slope, zero speed Object 3- negative slope, negative speed

  10. Graphing Instantaneous Speed • Instantaneous speed is the speed of an object at a certain point in the object’s path. • Instantaneous speed at a given point can be determined my measuring the slope of the line that is tangent to that point on the position-time graph.

  11. Example 3: • A tortoise and a hare go on a race. The tortoise crawls at 5 cm/s while the hare travels at 300 cm/s. However, the hare stops for 50 seconds during the race. The tortoise crosses the finish line first. • (a) How long did the hare stop during the race if the tortoise just crossed the finish line before the hare? • (b) How far did the tortoise travel?

  12. Example 4: • I want to average 55 miles/hour on a trip. On local residential streets, which I am on for only half the distance of the trip, I can travel an average speed of 35 miles/hour. How fast do I need to go the other half of the distance of the trip?

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