MSB General Science Std 07 | Effects of Heat | Expansion and Contraction of Solids

Summary

This video script explores the practical applications of the expansion and contraction of substances. It explains why gaps are left in railway tracks during summer to prevent bending and accidents, and how blacksmiths use heat to expand iron rims to tightly fix them onto cart wheels. Additionally, it discusses how electric wires expand in the heat, forming loops, and why materials like copper and aluminum are used for this purpose. The script highlights the importance of understanding thermal expansion in everyday objects and engineering solutions.

Takeaways

• 🌡️ Thermal expansion and contraction of substances occurs due to changes in temperature.
• 🚂 Gaps are left between railway track joints to allow for expansion in hot weather and due to friction from trains.
• ⚠️ Without gaps, railway tracks could bend, increasing the risk of accidents.
• 🛞 Iron rims on cart wheels are made slightly smaller than the wheel diameter to use expansion for fitting.
• 🔥 Heating the iron rim increases its diameter, allowing it to fit over the wheel.
• 💧 Pouring cold water on the heated rim causes it to contract and fit tightly onto the wheel.
• ⚡ Electric wires expand in hot weather, which can increase their length.
• 🔗 Copper and aluminium are used for wires because they expand predictably and safely.
• ➰ Loops are formed in electric wires to accommodate expansion and prevent snapping.
• 🔧 Practical applications of thermal expansion include engineering safety, mechanical fittings, and electrical installations.

Q & A

Why is a gap left between the joints of railway tracks?

A gap is left to allow for the expansion of railway tracks due to heat in summer or when trains pass over them. Without these gaps, the tracks could bend, causing accidents.

What causes railway tracks to expand when a train passes over them?

The friction between the train wheels and the tracks generates heat, which causes the metal of the tracks to expand, increasing their volume and length.

How does a blacksmith use the expansion of solids when fixing an iron rim on a cart wheel?

The blacksmith heats the iron rim, causing it to expand. The expanded rim is placed onto the wheel, and when cooled with water, it contracts, fitting tightly around the wheel.

Why is the diameter of the iron rim made slightly smaller than the wheel before heating?

The rim is made smaller so that when it is heated and expands, it can be fitted onto the wheel. Upon cooling, it contracts to form a tight fit.

Why are loops formed in electric wires during summer?

Loops are formed because electric wires expand in length due to extreme heat. Making loops allows the wires to accommodate expansion without snapping or tension.

Why are electric wires typically made of copper or aluminum?

Copper and aluminum are used because they are good conductors of electricity and also expand significantly when heated, which is considered in their installation to prevent damage.

What practical applications of expansion and contraction can be observed in daily life?

Practical applications include gaps in railway tracks, fitting iron rims on cart wheels, and loops in electric wires to accommodate thermal expansion.

What could happen if railway tracks did not have gaps for expansion?

Without gaps, tracks could bend or buckle due to expansion, creating a risk of derailment and accidents.

How does temperature affect the volume of solid materials like iron or copper?

When solid materials are heated, their volume increases due to the expansion of particles, and when cooled, they contract as the particles come closer together.

Why is cold water poured over the iron rim after it is placed on the wheel?

Cold water cools the rim, causing it to contract and fit tightly onto the wheel, ensuring a secure and stable attachment.

How does thermal expansion influence the design of infrastructure and machinery?

Thermal expansion must be considered to prevent damage; gaps, loops, and allowances are built into structures and machinery to accommodate changes in size due to temperature variations.