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# Lesson 1: The Tangent and Velocity Problems

## on Feb 01, 2008

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Finding the speed of a moving object (without a speedometer) and finding the slope of a line tangent to a curve are two interesting problems. It turns out there are models of the same process.

Finding the speed of a moving object (without a speedometer) and finding the slope of a line tangent to a curve are two interesting problems. It turns out there are models of the same process.

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## Lesson 1: The Tangent and Velocity ProblemsPresentation Transcript

• Section 2.1 The Tangent and Velocity Problems Math 1a February 1, 2008 Announcements Grab a bingo card and start playing! Syllabus available on course website Homework for Monday 2/4: Practice 2.1: 1, 3, 5, 7, 9 Turn-in 2.1: 2, 4, 6, 8 Complete the ALEKS initial assessment (course code QAQRC-EQJA6)
• Outline Bingo Velocity Tangents
• Outline Bingo Velocity Tangents
• Hatsumon Problem My speedometer is broken, but I have an odometer and a clock. How can I determine my speed? | | | | | | | | | −4 −3 −2 −1 0 1 2 3 4
• Outline Bingo Velocity Tangents
• A famous solvable problem Problem Given a curve and a point on the curve, ﬁnd the line tangent to the curve at that point.
• A famous solvable problem Problem Given a curve and a point on the curve, ﬁnd the line tangent to the curve at that point. But what do we mean by tangent?
• A famous solvable problem Problem Given a curve and a point on the curve, ﬁnd the line tangent to the curve at that point. But what do we mean by tangent? In geometry, a line is tangent to a circle if it intersects the circle in only one place. •
• Towards a deﬁnition of tangent This doesn’t work so well for general curves, though:
• Towards a deﬁnition of tangent This doesn’t work so well for general curves, though: Is this a tangent line?
• Towards a deﬁnition of tangent This doesn’t work so well for general curves, though: Is this a tangent line? • Is this a tangent line?
• Towards a deﬁnition of tangent This doesn’t work so well for general curves, though: Is this a tangent line? • Is this a tangent line? We need to think of tangency as a “local” phenomenon.
• Tangent A line L is tangent to a curve C at a point P if L and C both go through P, and L and C have the same “slope” at P. Slope of L = “m” in y = mx + b rise = run f (x) − f (a) Slope of C at a ≈ where x ≈ a x −a
• Tangent as a limiting process To ﬁnd the tangent line through a curve at a point, we draw secant lines through the curve at that point and ﬁnd the line they approach as the second point of the secant nears the ﬁrst.
• Tangent as a limiting process To ﬁnd the tangent line through a curve at a point, we draw secant lines through the curve at that point and ﬁnd the line they approach as the second point of the secant nears the ﬁrst. √ For instance, it appears the tangent line to y = x through (4, 2) has slope 0.25.
• Same thing! The inﬁnitesimal rate of change calculation is the same in both cases: ﬁnding velocities or ﬁnding slopes of tangent lines.
• General rates of change The rate of change of f (t) at time t1 = the slope of y = f (t) at the point (t1 , f (t1 )). units of f (t) The units are . units of t