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Introduction to Calculus. Rate of Change. Review of Rates. Definition. Practice. A rate is a comparison between two quantities of different kinds A common rate that we use is speed , speed is the rate of distance travelled per unit of time.
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Introduction to Calculus Rate of Change
Review of Rates Definition Practice • A rate is a comparison between two quantities of different kinds • A common rate that we use is speed, speed is the rate of distance travelled per unit of time • Joseph typed 213 words in 3 minutes and made 6 errors, whereas Marie typed 260 words in 4 minutes and made 7 errors. Compare their performance using rates. • Who types faster? • Who was more accurate? • Karsten’s pulse rate was measured at 67 beats/minute • What does that rate mean? • How many heart beats would Karsten expect to have each hour?
Average Rate of Change • Consider a trip from Adelaide to Melbourne. The following table gives places along the way, distances travelled and time taken.
Average Rate of Change • If we graphed the points in the table the average rate of change (the average speed) between two places would be the slope (or gradient for IB) of the line that connects the two points that represent each place
So what is the average rate of change of a linear graph??????? The slope or gradient of the line.
Average Rate of Change from Curved Graphs Example: Mice Colony • The number of mice in a colony was recorded on a weekly basis. • Estimate the average rate of increase in population for : • The period from week 3 to week 6 • The seven week period • What is the overall trend with regard to population over this period?
Average Rate of Change from Curved Graphs • The average rate of change between two points on the curve is the gradient of the chord (or secant) connecting these two points. The period from week 3 to week 6: Gradient= approximately 43 mice/week The seven week period: Gradient= approximately 38 mice/week
Instantaneous Rates of Change • A moving object such as a car, an airplane, or a runner has variable speed. At a particular moment in time the speed of the object is called the instantaneous speed. • How do you find instantaneous rate of change?
Text Book Demo A ball bearing is dropped from the top of a tall building. The distance fallen after t seconds is recorded an the graph of distance against time is obtained. The question is, “What is the speed of the ball bearing at t=2 seconds?”
Text Book Demo • What is the gradient of the chord when M is at the point where t is • 3 • 2.5 • 2.1 • 2.01 • When M reaches F what happens? Why? • What do you suspect is the speed of the ball bearing at t=2? This is the instantaneous speed of the ball bearing at this instant.
Instantaneous Rate of Change Conclusions from Demo • If you find the rate of change between F and another point, M, then as you make the x value of M closer to the x value of F the rate of change between them gets closer to the instantaneous rate of change at the point F. • The instantaneous rate of change at a particular point is the gradient of the tangent to the graph at that point.
Instantaneous Rate of Change Instantaneous Rate of Change at point P = Gradient of the Tangent to the Graph at point P = Gradient of the function at point P
How do you find the gradient of the tangent line of a graph at a certain point? Graphically Draw the tangent at that point and find the gradient Problems? Not very accurate, have to approximate the tangent line. Better Method? THE DERIVATIVE!!!!!!!!!
