Proof of the Second Shifting Theorem - 1.5 | 4. Second Shifting Theorem | Mathematics - iii (Differential Calculus) - Vol 1
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Interactive Audio Lesson

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Introduction to the Second Shifting Theorem

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0:00
Teacher
Teacher

Today, we will discuss the Second Shifting Theorem in Laplace Transforms. Can anyone tell me why we might need to handle delayed functions in engineering?

Student 1
Student 1

In control systems, inputs often start after some delay.

Teacher
Teacher

Exactly! This theorem helps us manage those delays by using the Heaviside step function to define when a function becomes active. What can you tell me about the Heaviside function?

Student 2
Student 2

It’s a function that jumps from 0 to 1 at a certain point, right?

Teacher
Teacher

Correct! It models the delayed signals we see in real-world applications.

The Statement of the Theorem

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Teacher
Teacher

The theorem states that if the Laplace transform of f(t) is F(s), then the transform of f(t - a)u(t) is e^(-as)F(s). Can someone explain what each part means?

Student 3
Student 3

Here, f(t - a) represents the delayed function, and u(t) ensures it activates after time a.

Student 4
Student 4

And e^(-as) is the exponential factor that modifies the transform!

Teacher
Teacher

Exactly! Remember this relationship, as it simplifies our computations with delayed functions.

Proof of the Theorem

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Teacher
Teacher

Let's delve into the proof. We begin by setting up our integral for the Laplace transform of f(t - a)u(t). Can anyone tell me why we integrate from a to infinity?

Student 1
Student 1

Because the Heaviside function u(t) is zero before time a!

Teacher
Teacher

Exactly! Now, if we substitute Ο„ = t - a, how would our limits change?

Student 2
Student 2

They change to Ο„ from 0 to infinity.

Teacher
Teacher

Perfect! This helps confirm that the theorem holds. Who can summarize what we’ve learned about the proof?

Student 3
Student 3

We use substitution and properties of the Laplace transform to arrive at the exponential factor!

Applications of the Second Shifting Theorem

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Teacher
Teacher

Now that we understand the theorem, let's discuss its applications. Can anyone provide an example of where we might use the Second Shifting Theorem?

Student 4
Student 4

In electrical circuits, for signals that start with a delay, like a switch turning on.

Teacher
Teacher

Right! It’s also used in mechanical systems and signal processing. Understanding these applications helps in analyzing real-world systems.

Introduction & Overview

Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.

Quick Overview

The Second Shifting Theorem provides a method to transform delayed functions in the Laplace domain.

Standard

In this section, we explore the Second Shifting Theorem of Laplace Transforms, which is vital for modeling and analyzing systems with delayed inputs. The theorem utilizes the Heaviside step function to define delayed functions and facilitates the transformation of such functions by introducing an exponential factor in the Laplace domain.

Detailed

Proof of the Second Shifting Theorem

The Section covers the Second Shifting Theorem, an essential property in Laplace Transforms used to analyze time-delayed functions. It begins by stating the theorem formally, connecting the Laplace Transform of a shifted function to its original transform multiplied by an exponential factor. The prominent role of the Heaviside unit step function is emphasized, as it activates signals that have delays. The proof is explored in detail, illustrating how the substitution of variables helps confirm the theorem's validity. Lastly, practical applications of the theorem in various fields underscore its significance in engineering and mathematics.

Audio Book

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Introduction to the Proof

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Let 𝑓(𝑑) be a function such that β„’{𝑓(𝑑)} = 𝐹(𝑠). Now consider 𝑓(π‘‘βˆ’π‘Ž)𝑒 (𝑑). Its Laplace Transform is:

β„’{𝑓(π‘‘βˆ’π‘Ž)𝑒 (𝑑)} = ∫ π‘’βˆ’π‘ π‘‘π‘“(π‘‘βˆ’π‘Ž)𝑒 (𝑑)𝑑𝑑

Since 𝑒 (𝑑) = 0 for 𝑑 < π‘Ž, the limits reduce:

Detailed Explanation

This chunk introduces the function we are interested in: 𝑓(𝑑). We know its Laplace transform is represented as 𝐹(𝑠). We are now considering a modified version of this function, which is delayed by π‘Ž units and multiplied by the Heaviside unit step function, 𝑒 (𝑑), ensuring the function starts only after the time 𝑑 equals π‘Ž. By establishing the Laplace transform of this delayed function, we prepare to analyze how it changes compared to the original function.

Examples & Analogies

Imagine you have a light switch that does not turn on until you press it at a specific time. The original function (light turning on) represents the switch being functional. However, introducing a delay (like pressing the switch at a later time) modifies the original action (light turning on), similar to how we analyze functions delayed by π‘Ž.

Adjusting the Limits of Integration

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β„’{𝑓(π‘‘βˆ’π‘Ž)𝑒 (𝑑)} = ∫ π‘’βˆ’π‘ π‘‘π‘“(π‘‘βˆ’π‘Ž)𝑑𝑑

Use substitution: 𝜏 = π‘‘βˆ’π‘Ž β‡’ 𝑑 = 𝜏+π‘Ž β‡’ 𝑑𝑑 = π‘‘πœ

Limits: When 𝑑 = π‘Ž, 𝜏 = 0; when 𝑑 = ∞, 𝜏 = ∞

Detailed Explanation

In this part, we are adjusting the limits of integration based on our substitution where we define a new variable 𝜏. This means that as we change variables, we also change the boundaries of our integral. The integral's lower limit changes from π‘Ž to 0, while the upper limit remains at infinity. This transformation is crucial as it simplifies the integral we will evaluate in the next steps.

Examples & Analogies

Think of this like changing the way you measure a distance. If you originally measure from point A to point B (limits), but then you decide to start your measurements at point A and refer to all distances in relation to point A, you end up adjusting where 'point A' is. Similarly, our limits of integration now reference our new variable.

Evaluating the Integral

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β„’{𝑓(π‘‘βˆ’π‘Ž)𝑒 (𝑑)} = ∫ π‘’βˆ’π‘ (𝜏+π‘Ž)𝑓(𝜏)π‘‘πœ = π‘’βˆ’π‘Žπ‘ βˆ« π‘’βˆ’π‘ πœπ‘“(𝜏)π‘‘πœ

Thus,
β„’{𝑓(π‘‘βˆ’π‘Ž)𝑒 (𝑑)} = π‘’βˆ’π‘Žπ‘ πΉ(𝑠)

Detailed Explanation

Here, we begin evaluating the integral after substituting our new variable. We notice that the term 𝑒^(-π‘Žπ‘ ) can be factored out of the integral. What remains is just the integral of the original function's Laplace transform. This amounts to demonstrating that the Laplace transform of the delayed function is simply the original Laplace transform multiplied by an exponential factor adjusting for the delay.

Examples & Analogies

Picture a bakery that adjusts its baking schedule. If a recipe calls for certain ingredients and the baker learns that the process will start 5 minutes later (the delay), they can account for this delay to ensure that the end product still comes out delicious at the right time by just adjusting the timing of when the ingredients are put in the oven. Similarly, we adjust our function using an exponential factor for the delay.

Definitions & Key Concepts

Learn essential terms and foundational ideas that form the basis of the topic.

Key Concepts

  • Second Shifting Theorem: A method to handle delayed functions in the Laplace domain.

  • Heaviside Step Function: A function that ensures a signal starts at a specific time.

  • Exponential Factor: The term e^(-as) that modifies the Laplace transform of a delayed function.

Examples & Real-Life Applications

See how the concepts apply in real-world scenarios to understand their practical implications.

Examples

  • Example: Applying the theorem to find the Laplace transform of (t - 2)Β²u(t) yielded 2e^(-2s)/sΒ³.

  • Example: Finding β„’{sin(t - Ο€)u(t)} produced e^(-Ο€s)/(sΒ² + 1).

Memory Aids

Use mnemonics, acronyms, or visual cues to help remember key information more easily.

🎡 Rhymes Time

  • To shift the time, add e to the rhyme; with f and u, you’ll adhere to the line.

πŸ“– Fascinating Stories

  • Imagine a party where guests arrive at different times. The Heaviside function opens the door at a set time, illustrating when a function starts.

🧠 Other Memory Gems

  • Remember 'SHeEf' for Second Shifting Theorem: S=Shifting, H=Heaviside, E=Exponential, f=function.

🎯 Super Acronyms

Use 'Tumeric' to remember Second Shifting, Itemized as T=Theorem, U=Shift, M=Multiply, E=Exponential, R=Real-world, I=Input, C=Compute.

Flash Cards

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Glossary of Terms

Review the Definitions for terms.

  • Term: Laplace Transform

    Definition:

    An integral transform that converts a time-domain function into a complex frequency domain function.

  • Term: Heaviside Step Function

    Definition:

    A mathematical function that is zero for negative time and one for non-negative time, used to model sudden changes.

  • Term: Second Shifting Theorem

    Definition:

    A property of the Laplace transform which states that the transform of a delayed function can be expressed in terms of the transform of the original function multiplied by an exponential factor.