Materi Pemuaian Kelas 7 SMP

Summary

In this educational video, the concept of thermal expansion is explored, explaining how materials expand when heated. The teacher uses real-world examples such as railway tracks, power cables, and window frames to illustrate the practical applications of thermal expansion in daily life. The video also covers the mathematical formula for calculating linear expansion and includes an example problem for clarity. Additionally, it touches on surface and volume expansions, with a focus on how these principles are applied in engineering and design to prevent damage or inefficiencies in various systems.

Takeaways

• 😀 Thermal expansion is the increase in size of materials when heated, and contraction occurs when cooled.
• 😀 Solid, liquid, and gas all undergo thermal expansion, although their rates may vary.
• 😀 Railway tracks have gaps to allow for thermal expansion; without these gaps, the tracks could warp and become dangerous.
• 😀 Electrical cables are designed to be slack so they can expand and contract with temperature changes without breaking.
• 😀 Window frames are made slightly larger than the glass to prevent it from breaking when the glass expands in the heat.
• 😀 Bimetallic strips, used in devices like thermostats, bend when heated due to the different expansion rates of the metals.
• 😀 The formula to calculate the final length of an object after heating is: l = l0(1 + αΔt), where l0 is the initial length, α is the coefficient of expansion, and Δt is the change in temperature.
• 😀 To calculate the temperature change, subtract the initial temperature from the final temperature: Δt = T2 - T1.
• 😀 Expansion can also affect areas and volumes, with formulas for area expansion (β = 2α) and volume expansion (γ = 3α).
• 😀 Understanding thermal expansion is crucial for practical applications in everyday life, such as the design of bridges, pipes, and even food packaging.

Q & A

What is thermal expansion?

Thermal expansion is the increase in the size (length, area, or volume) of a material when its temperature rises. This occurs not only in solids but also in liquids and gases.

What happens when a material undergoes thermal expansion?

When a material undergoes thermal expansion, its size increases. This can be seen as an increase in length, width, or thickness, depending on the material. If the temperature decreases, the material contracts.

Why are gaps left between railway tracks?

Gaps are left between railway tracks to accommodate the expansion of the metal rails when the temperature rises. If there were no gaps, the expanding rails could warp or buckle, causing dangerous conditions for trains.

Why are electrical cables on highways left loose during installation?

Electrical cables are left loose because they expand in hot weather and contract in cooler temperatures. If the cables were too tight, they could snap when they contract at night.

How does the expansion of glass in a window frame work?

The window frame is designed to be slightly larger to allow for the glass to expand when the temperature increases. This prevents the glass from breaking due to thermal expansion.

What is a bimetallic strip and how does it work?

A bimetallic strip is made from two different metals that expand at different rates. When heated, the strip bends in the direction of the metal with the lower rate of expansion. This property is used in devices like thermostats, circuit breakers, and thermometers.

Why are bottles of liquid like syrup not filled to the top?

Bottles of liquids such as syrup, ketchup, or oil are not filled to the top to allow room for the liquid to expand when the temperature increases, preventing spills or overflow.

How does thermal expansion affect car tires?

Thermal expansion in car tires occurs when the air inside the tires heats up, causing the gas to expand. If the tires are overfilled, the increased pressure from the expansion could cause the tire to burst.

What is the formula for calculating the change in length of a material due to thermal expansion?

The formula to calculate the change in length is: L = L0 × (1 + α × ΔT), where L is the final length, L0 is the initial length, α is the coefficient of linear expansion, and ΔT is the change in temperature.

How is the change in area and volume due to thermal expansion calculated?

The change in area is calculated by multiplying the coefficient of linear expansion by 2 (β = 2α), and the change in volume is calculated by multiplying the coefficient of linear expansion by 3 (γ = 3α). These formulas are used to determine how the area and volume of materials change when heated.