Types of Velocities Sept 4 2008 Uniform Motion

Types of Velocities Sept. 4, 2008

Uniform Motion n The velocity (the rate of change of a position) of an object remains constant n Example: a tortoise and a plane may move at different velocities but they may both be travelling at a constant velocity

Non-Uniform Motion n The velocity is changing n The speed or the direction may be changing n Example: rocket ship taking off (speed changes)

Recall: Average Velocity n Average velocity gives us the average displacement over time- we don’t know what happens between the final and initial points n Need more data points to verify if an object is moving uniformly or nonuniformly

Position-Time Graphs n We can plot the position of an object with respect to time to help us better visualize velocity n For example, if we were to time and measure the displacement of a skateboarder:

Time (s) 0. 0 1. 3 2. 6 Position (m[E]) 0. 0 12 24 3. 9 5. 2 6. 5 36 48 60

The graph would look like 70 Position (m) vs. Time (s) 60 50 40 30 20 10 0 0 -10 1 2 3 4 5 6 7

What is the significance of the straight line? n Slope = rise/run n Slope = displacement/change in time n Slope of a position-time graph tells you the velocity n If the line is straight…?

Does this mean the velocity was constant? n It is hard to know if the velocity was truly constant n The average velocity may be the same between test points but we cannot know for sure if there wasn’t change in between each point n Can only TRULY know if there is continuous data (information for every second/split second/nanosecond)

Instantaneous Velocity n Average velocity does not always tell the story well n Instantaneous velocity tells us the speed “at that moment” n Think of it as finding the slope of a position graph of one point (finding the tangent)

What is a tangent? n A tangent is a line that only touches a curve (ex. Your position/time curve) in one place n The slope of the tangent tells you the instantaneous velocity