Topic: Position-Time Graphs Unit 1: Chapter 1 and 2

What is cause and effect? In experiments we are looking for a cause and effect relationship Want to see how changing one variable effects another How changes to your manipulated variable effect your responding variable Example: In last week’s lab, the position of the photogate was the ____________ variable and the speed of the car was the ____________ variable.

What do patterns in data show us? Patterns in data allow us to see relationships between variables Graphing data provides a visual image of the relationships between variables in a set of data Strong pattern = Strong relationship Weak/no pattern = no relationship

How do graphs show strong and weak relationships? Strong relationship Small change in one variable makes a big change in another Weak relationship Changes in one variable has little to no effect on the other variable

How do we represent motion with a graph? The motion of an object can be represented by a position-time graph Definition: Position-time graphs show where things are at different times X-axis: Represents time Y-axis: Represents position relative to the starting point

Why are position-time graphs useful? Suppose you take a car trip that includes 1.5 hours of driving and a half-hour rest stop, for a total time of 2 hours. You drive a total distance of 90 miles in a straight line. What is your average speed? 90 miles/2hours = 45mph Did you really drive for 2 hours without stopping? No You really covered the 90 miles in 1.5 hours at a speed of 60mph and stopped (with zero speed) for a half hour

Figuring out velocity from a position-time graph In a position-time graph the velocity of an object can be calculated using the slope of the graph line Steeper line = greater slope = faster the object’s motion Slope = average velocity of the object

How do you calculate slope? Slope equation Using the slope equation: Pick two points on the line and determine their coordinates Determine the difference in y-coordinates of these two points (rise) Determine the difference in x-coordinates of these two pointes (run) Divide the difference in y-coordinates by the difference in x-coordinates

Practice