Lesson 4: How Fast? - Physics Notes PDF

Lesson 4 How Fast?  Focus Question How do you describe how fast something is moving?  New Vocabulary average velocity average speed instantaneous velocity  Review Vocabulary absolute value: a number that is equal in value to a given real number but is not negative ...

Lesson 4 How Fast?  Focus Question How do you describe how fast something is moving?  New Vocabulary average velocity average speed instantaneous velocity  Review Vocabulary absolute value: a number that is equal in value to a given real number but is not negative  Velocity and Speed Consider the position- time graph of two joggers. The slope of a position-time graph for an object is the object’s average velocity, which is represented by the equation:  Velocity and Speed The sign of the slope tells you what direction the object is moving.  Velocity and Speed The slope’s absolute value is the object’s average speed, which is the distance traveled divided by the time taken to travel that distance.  Velocity and Speed The speed and direction of an object at a particular instant is called the instantaneous velocity.  Velocity and Speed Use with Example Problem 3. Problem What is the average velocity of the object whose motion is represented in this graph? What is its average speed? Response Select two points on the graph to use to find the slope.  Equation of Motion Recall that a straight line can be represented by the equation y = mx + b Similarly, a straight line on a position-time graph can be represented with the equation  Equation of Motion v 12 m/s west Use with Example Problem 4. Problem A car is initially 6.0 m east of the origin. It drives west at a speed of 12 m/s. What is its position after 1.2 s? x ? Response SKETCH AND ANALYZE THE PROBLEM Sketch the situation. SOLVE FOR THE UNKNOWN List the knowns and unknowns. Use the relationship between displacement, velocity, and time.  Quiz 1 How do you find the average speed of. an object from a position-time graph? A Find the slope C Find the change in between two the x values. points on the line. B Find the absolute D Find the change in value of the slope the y values. of the line. CORREC T  Quiz 2 What is the speed and direction of an. object at a particular instant of time? A average velocity B average speed C instantaneous CORREC velocity T D instantaneous speed  Quiz 3 Which is the total distance traveled. divided by the time taken to travel that distance? A instantaneous C average speed speed CORREC T B instantaneous D average velocity velocity  Quiz 4 Heather. and Juanita are traveling east. What is Heather’s average speed? A 3.0 km/h C 2.8 km/h CORREC T B 4.8 km/h D 6.0 km/h  Quiz 5 In a mathematical representation of a. straight line on a position-time graph, what quantity is represented by the y- intercept? A the time taken C the final position B the average D the initial position velocity CORREC T