Proof of the Division by t Rule - 8.1.3 | 8. Division by t (Inverse of Multiplication by s) | Mathematics - iii (Differential Calculus) - Vol 1
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8.1.3 - Proof of the Division by t Rule

Practice

Interactive Audio Lesson

Listen to a student-teacher conversation explaining the topic in a relatable way.

Introduction to the Division by t Rule

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0:00
Teacher
Teacher

Today, we'll explore the Division by t rule in Laplace transforms. Can anyone tell me what they think happens when we divide a function by time?

Student 1
Student 1

I think it relates to some integration because dividing typically means breaking something down.

Teacher
Teacher

Exactly! Dividing by time in the time domain corresponds to integrating in the s-domain. This is our key takeaway today!

Student 2
Student 2

So, does that mean we can use it to solve problems involving differential equations?

Teacher
Teacher

Absolutely! Understanding how division and integration relate is crucial for effectively solving such equations.

Student 3
Student 3

Are there any special conditions for this property to work?

Teacher
Teacher

Great question! The function must be piecewise continuous and of exponential order.

Teacher
Teacher

In summary, the Division by t rule is a vital property that allows us to transform complex time-domain functions into manageable s-domain forms.

Proof of the Division by t Rule

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0:00
Teacher
Teacher

Now, let's look at the proof of the Division by t rule. Who can remind us what the Laplace transform definition is?

Student 4
Student 4

Isn't it \( \mathcal{L}\{f(t)\} = \int_{0}^{\infty} f(t) e^{-st} dt \) ?

Teacher
Teacher

Exactly! And when we apply this to \( \frac{f(t)}{t} \), we end up switching integration orders using Fubini's theorem.

Student 1
Student 1

So, we use the inversion theorem as well to derive our target result?

Teacher
Teacher

Yes! Fubini allows us this switch, letting us express the original division as an integral of the transformed function.

Student 2
Student 2

Is this why we look up results in Laplace tables for simpler cases?

Teacher
Teacher

Exactly! Tables provide pre-calculated solutions which can save us time in complex problems.

Teacher
Teacher

In conclusion, the proof demonstrates how integral calculus bridges our functional transformation from time to s-domain.

Applications of the Division by t Rule

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Teacher
Teacher

Let’s examine how the Division by t rule plays out in real-world applications. Where do you think this might be useful?

Student 3
Student 3

Maybe in control systems where input signals change over time?

Teacher
Teacher

Exactly! It’s widely used in control system analysis, particularly for time-varying inputs.

Student 4
Student 4

What about signal processing? I imagine it’d help when dealing with transformations of signals.

Teacher
Teacher

Right again! Filtering and signal manipulation often rely on this property.

Student 2
Student 2

And how does it relate to electrical engineering?

Teacher
Teacher

The rule helps analyze decaying signals, particularly those involving transient responses in circuits.

Teacher
Teacher

To summarize, the Division by t rule is not just theoretical; it has practical applications across various engineering fields.

Introduction & Overview

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

Quick Overview

This section details the Division by t property in Laplace transforms, its proof, and its applications.

Standard

The Division by t rule describes how division by time in the time domain corresponds to integration in the Laplace s-domain. This property is vital for solving differential equations and analyzing control systems, and the section provides mathematical proof along with practical examples.

Detailed

Detailed Summary

In the realm of Laplace transforms, there exists a crucial property known as the Division by t Rule, which states that dividing a time-domain function by time corresponds to integrating its Laplace transform. This section provides a comprehensive exploration of this property, starting with mathematical formulations and culminating in proofs and examples.

Key Concepts

  1. Division by t Rule: The Laplace transform of
    \[ \mathcal{L}\{\frac{f(t)}{t}\} = \int_{0}^{\infty} F(u) \; du \]
    where \( F(s) = \mathcal{L}\{f(t)\} \).
  2. Proof of the Rule: The section discusses the definition of the Laplace transform and employs the Laplace inversion theorem and Fubini's theorem to derive the Division by t Rule, establishing a foundational link between time and the s-domain.
  3. Important Considerations: The divisive property is conversely related to the multiplication by t rule and is typically applicable when the function is piecewise continuous and of exponential order.
  4. Applications: The Division by t property has significant applications in control systems, signal processing, differential equations, and electrical engineering, enabling solutions for systems with time-varying inputs.
  5. Examples: Practical implementations highlight how to derive the Laplace transforms of specific functions through the Division by t approach, providing concrete contexts for its use.

Audio Book

Dive deep into the subject with an immersive audiobook experience.

Understanding the Laplace Transform

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Let us begin with the Laplace transform definition:

$$\mathcal{L}\{\frac{f(t)}{t}\} = \int_0^{\infty} \frac{f(t)e^{-st}}{t} dt$$

Let $F(s) = \mathcal{L}\{f(t)\} = \int_0^{\infty} f(t)e^{-st}dt$

Detailed Explanation

In this chunk, we start with the definition of the Laplace transform. The Laplace transform of a function f(t) is defined as the integral of f(t) multiplied by e^(-st) from 0 to infinity. When considering the function divided by t, it changes how we compute the Laplace transform, leading us to the specific rule we are studying.

Examples & Analogies

Imagine you are measuring the energy output of a machine over time. The total energy at a given time depends not only on how much energy is being produced but also how long the machine has been running. Just like energy output measured per unit time gives a different perspective, dividing functions by time in Laplace transforms helps to analyze their behavior in different domains.

Using Theorems for Derivation

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Now consider the Laplace transform of $\frac{f(t)}{t}$. Use the Laplace inversion theorem and Fubini's theorem to switch the order of integration. The derivation is somewhat advanced, so we often rely on the known result:

$$\mathcal{L}\{\frac{f(t)}{t}\} = \int_0^{\infty} F(u) du$$

Detailed Explanation

This chunk introduces the idea of applying mathematical theorems like the Laplace inversion theorem and Fubini’s theorem, which allows you to swap the order of integration in a double integral. This manipulation leads to a simpler form for calculating Laplace transforms, providing a way to utilize known results to find new ones efficiently.

Examples & Analogies

Imagine organizing a large event with multiple activities. Instead of assessing each activity separately, you could group similar ones together - much like switching the order of integration. This method simplifies the overall assessment process, giving you a more manageable way to understand the entire event's success.

Division by t Rule Application

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This provides a powerful method to find the Laplace transform of a function divided by $t$, especially when $F(s)$ is known.

Detailed Explanation

Here, the focus is on the practical implications of the Division by t Rule. It highlights that once you have the Laplace transform $F(s)$ of a function, you can apply this rule to easily calculate the Laplace transform of the original function divided by t. This method is particularly valuable in fields like engineering and physics, where this kind of transformation frequently occurs.

Examples & Analogies

Consider a chef who knows how to make a dish quickly. If they want to create a smaller portion, they can easily adjust the ingredients using the same method. Similarly, once you know how to transform a function with the Laplace transform, applying it to variations like division by t becomes straightforward.

Criteria for Validity

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Applicable only when $\frac{f(t)}{t}$ is piecewise continuous and of exponential order.

Detailed Explanation

This part emphasizes important conditions for the application of the Division by t Rule. A function must be piecewise continuous (meaning it can be broken into intervals that have defined behavior) and must grow at a manageable rate (exponential order) to ensure that its Laplace transform exists. Understanding these requirements is crucial for correctly applying this rule.

Examples & Analogies

Think about running a race where only certain routes are officially allowed. If you venture off-path (like using a function that doesn’t meet the continuity requirement), you may find yourself lost. Being aware of the rules ensures that you stay on course and finish successfully.

Definitions & Key Concepts

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

Key Concepts

  • Division by t Rule: The Laplace transform of

  • \[ \mathcal{L}\{\frac{f(t)}{t}\} = \int_{0}^{\infty} F(u) \; du \]

  • where \( F(s) = \mathcal{L}\{f(t)\} \).

  • Proof of the Rule: The section discusses the definition of the Laplace transform and employs the Laplace inversion theorem and Fubini's theorem to derive the Division by t Rule, establishing a foundational link between time and the s-domain.

  • Important Considerations: The divisive property is conversely related to the multiplication by t rule and is typically applicable when the function is piecewise continuous and of exponential order.

  • Applications: The Division by t property has significant applications in control systems, signal processing, differential equations, and electrical engineering, enabling solutions for systems with time-varying inputs.

  • Examples: Practical implementations highlight how to derive the Laplace transforms of specific functions through the Division by t approach, providing concrete contexts for its use.

Examples & Real-Life Applications

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

Examples

  • Example 1: Finding the Laplace transform of \( \frac{\sin(at)}{t} \) using the Division by t rule.

  • Example 2: Use the Division by t rule to find the Laplace transform of \( \frac{1 - \cos(at)}{t} \).

Memory Aids

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

🎡 Rhymes Time

  • When time you divide, integration's inside, Laplace says, you’ve got to abide.

πŸ“– Fascinating Stories

  • Imagine time as a cake, slicing it creates depth in flavor - that's what division by t does in Laplace!

🧠 Other Memory Gems

  • DIT: Divide In Time - means integrate in Laplace!

🎯 Super Acronyms

DTR

  • Division To Reveal - division by t reveals integration!

Flash Cards

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Glossary of Terms

Review the Definitions for terms.

  • Term: Laplace Transform

    Definition:

    An integral transform that converts a function of time into a function of a complex variable.

  • Term: Division by t Rule

    Definition:

    A property that indicates dividing a function by time in the time domain is equivalent to integrating its Laplace transform.

  • Term: Piecewise Continuous

    Definition:

    A function that is continuous within pieces of its domain but may have finite discontinuities.

  • Term: Exponential Order

    Definition:

    A function is of exponential order if it does not grow faster than an exponential function as time approaches infinity.