Dilatação Térmica - Brasil Escola

Summary

In this physics lesson, Professor Joab explains the concept of thermal expansion and contraction, detailing how substances expand when heated and contract when cooled. He highlights real-world applications such as gaps in train tracks and how hot water can help open jar lids. The lesson also covers linear expansion and the formula for calculating the change in length of solids when subjected to temperature changes. Using examples like iron and copper, the lesson demonstrates how different materials expand differently, providing a practical understanding of the principles of thermal expansion.

Takeaways

• 😀 Thermal expansion occurs when a substance experiences a temperature change, causing it to either expand (dilate) or contract.
• 😀 When a substance absorbs heat, its temperature increases, leading to thermal expansion, while cooling causes contraction.
• 😀 Thermal expansion and contraction happen in solids, liquids, and gases when exposed to temperature variations.
• 😀 In daily life, various items are designed to accommodate thermal expansion, such as the gaps between train tracks to allow for expansion in hot weather.
• 😀 In everyday examples, placing hot water on a metal lid can cause the metal to expand, making it easier to open.
• 😀 Increased temperature leads to more intense molecular vibration, which causes the particles in a substance to move further apart, resulting in expansion.
• 😀 Conversely, a decrease in temperature reduces molecular vibration, causing the particles to move closer together, leading to contraction.
• 😀 Different materials react differently to temperature changes, meaning some materials expand or contract more than others under the same temperature variation.
• 😀 In linear thermal expansion, the expansion happens along one dimension (length), as exemplified by a metal bar whose length increases with heat.
• 😀 The amount of expansion (ΔL) is directly proportional to both the initial length (L0) of the object and the change in temperature (ΔT).

Q & A

What is thermal expansion?

Thermal expansion refers to the increase in the size of a substance when its temperature rises. This occurs because the molecules in the substance vibrate more intensely and move farther apart as the temperature increases.

How does temperature affect the size of a substance?

When a substance gains heat, its temperature rises, and it expands. Conversely, when it loses heat and its temperature decreases, it contracts.

What is an example of thermal expansion in daily life?

One example is the spacing between railway tracks. Gaps are left between the tracks to allow for expansion when the metal heats up under the sun.

Why is it difficult to open metal jar lids?

Metal jar lids are difficult to open because they contract at lower temperatures. To help open them, hot water can be poured on the lid to cause the metal to expand, making it easier to remove.

How does molecular vibration relate to temperature?

Temperature is a measure of molecular vibration. As temperature increases, molecular vibration becomes more intense, causing the molecules to move farther apart, leading to expansion.

What is the difference between expansion and contraction?

Expansion occurs when a material is heated, causing its molecules to move farther apart. Contraction occurs when a material cools, causing its molecules to come closer together.

What is linear expansion?

Linear expansion refers to the expansion of a material in one dimension, specifically its length, when subjected to a change in temperature.

What is the formula for calculating linear expansion?

The formula for linear expansion is: ΔL = α × L₀ × ΔT, where ΔL is the change in length, α is the coefficient of linear expansion, L₀ is the initial length, and ΔT is the change in temperature.

What does the coefficient of linear expansion represent?

The coefficient of linear expansion (α) is a constant that represents how much a material expands per unit length for each degree of temperature change. Different materials have different coefficients.

What happens when two materials with different coefficients of expansion are subjected to the same temperature change?

The material with the higher coefficient of linear expansion will expand more than the one with a lower coefficient when both are subjected to the same temperature change.