Bab 3 Suhu, Kalor dan Pemuaian #3 (PEMUAIAN) | IPA SMP Kelas 7 | Sekolah Penggerak

Summary

This video lesson explores the concept of thermal expansion, demonstrating how materials expand when heated and contract when cooled. It explains how different materials exhibit varying degrees of expansion, with a focus on solids like metals. Real-life applications are highlighted, such as the design of train tracks, window installations, and electrical wiring. The principle of bimetallic strips, used in electrical devices and safety mechanisms, is introduced, explaining how two metals with different expansion rates work together to trigger actions like circuit interruption. The lesson emphasizes the importance of understanding thermal expansion in practical engineering and daily life.

Takeaways

• 😀 Thermal expansion (pemuaian) is the increase in size (length, area, or volume) of materials when heated.
• 😀 Different materials expand at different rates, and some expand more easily than others with small temperature increases.
• 😀 When a material is heated, its molecules or atoms vibrate faster, causing the material to expand.
• 😀 Cooling a material leads to contraction, known as 'penyusutan,' which reduces its size.
• 😀 Engineers account for thermal expansion and contraction when designing structures like bridges and buildings to ensure safety and functionality.
• 😀 Railroads are designed with gaps between rail sections to prevent expansion from heat, which could otherwise cause dangerous buckling.
• 😀 Windows are installed with gaps to accommodate the expansion of glass when heated, preventing breakage.
• 😀 Pouring hot water into a cold, wet glass can cause it to crack due to uneven expansion of the glass material.
• 😀 Electrical cables are installed loosely to prevent breaking from contraction during cold temperatures and expansion in heat.
• 😀 Bimetallic strips are used in electrical devices like circuit breakers to break the circuit when overheating occurs. Bimetals are two metals with different rates of expansion.
• 😀 The principle of bimetals is used in several applications, including fire alarms, thermostats, and electrical fuses, to prevent accidents due to excessive heat.

Q & A

What is thermal expansion and how does it occur?

Thermal expansion is the increase in the size of an object due to the heat it absorbs. When an object is heated, its atoms or molecules vibrate more rapidly, causing the object to expand in all directions, resulting in an increase in its length, area, or volume.

Why do some materials expand more easily than others?

Some materials have a higher coefficient of thermal expansion, meaning they expand more for the same temperature increase. This makes them more sensitive to changes in temperature, while others expand less even with significant temperature changes.

What happens to the size and density of metals when they are heated?

When metals are heated, their atoms vibrate faster, causing the metal to expand. As a result, the metal's volume increases and its density decreases because the mass remains constant while the volume increases.

What is the role of thermal expansion in construction?

In construction, understanding thermal expansion is crucial for building structures such as bridges, roads, and buildings. Engineers design these structures to accommodate expansion and contraction due to temperature changes, preventing damage like warping or cracking.

Why do railway tracks have gaps between them?

Railway tracks have gaps to allow for thermal expansion. When the metal rails heat up in the sun, they expand. If there were no gaps, the rails could bend or buckle, potentially causing accidents.

Why is there a gap between window frames and glass?

Window frames are designed with a gap to prevent the glass from cracking. When the temperature increases, the glass expands. If there were no gap, the glass could break because the expansion would be restricted.

What is the reason for a glass breaking when hot water is poured into it while it is still wet?

The glass may crack because the inner surface of the glass expands faster due to the hot water, while the outer surface, which is still cold and wet, does not expand as much. This creates internal stress, causing the glass to break.

How do electrical cables account for temperature changes?

Electrical cables are installed loosely to allow for thermal expansion and contraction. If the temperature drops, the cables shrink, and if it rises, they expand. The slack prevents the cables from breaking due to these changes.

What is bimetal, and how does it work?

Bimetal consists of two different metals with different coefficients of expansion bonded together. When heated, the metals expand at different rates, causing the bimetal to bend. This principle is used in devices like circuit breakers to detect temperature changes and prevent overheating.

How does the principle of bimetal work in a thermostat?

In a thermostat, the bimetallic strip bends as the temperature changes due to the different expansion rates of the metals. This bending can open or close a circuit, turning a device on or off to maintain a desired temperature.