Plastics and elastics, the role of remote sensing and GIS in environmental science, Kepler laws of planetary motion, and preservatives and antioxidants

Understanding the topic

This question moves from material science to environmental technology, astronomy and food science. The examiner expects accurate distinctions rather than long descriptions. For each part, identify the defining principle, explain how it works, and support it with carefully chosen examples. The printed word “Elastics” in part (a) is best understood as elastomers.

(a) What is difference between Plastics and Elastics? Explain briefly.

The printed term “Elastics” is not the usual technical category. In polymer science, the intended comparison is between plastics and elastomers. Both consist of long-chain polymers, but their molecular structures and mechanical behaviour differ.

Plastics can be moulded into a desired shape and normally retain that shape after the applied force is removed. Their polymer chains have limited freedom to move. Thermoplastics such as polyethylene and PVC soften on heating and can be remoulded. Thermosetting plastics such as Bakelite form dense cross-links during curing and cannot be reshaped by reheating. Plastics are used for containers, pipes, electrical insulation, furniture and machine parts.

Elastomers can be stretched, compressed or bent considerably and then recover most of their original shape. Their chains are flexible and coiled, with a small number of cross-links that prevent permanent sliding while allowing temporary extension. Natural rubber, silicone rubber and neoprene are common examples. They are used in tyres, seals, gloves, hoses and shock absorbers.

Thus, the central distinction is not simply that one material is hard and the other is soft. Plastics are designed mainly for shape retention and mouldability, whereas elastomers are designed for large reversible deformation and resilience.

(b) What is role of Remote sensing and GIS in environmental Science? Discuss briefly.

Remote sensing obtains information about the Earth without direct contact, usually through sensors on satellites, aircraft or drones. These sensors record reflected or emitted energy in visible, infrared, microwave and other bands. Geographic Information Systems, or GIS, store, combine, analyse and display data linked to location.

Remote sensing provides repeated coverage of large or inaccessible areas. It can identify changes in forests, crops, glaciers, wetlands, coastlines and urban land. Thermal data help map heat islands and wildfires, while multispectral observations can indicate vegetation stress, sediment, algal blooms or changes in surface water. Radar can acquire information through clouds and can help map floods or ground deformation.

GIS gives these observations analytical meaning. A researcher can overlay satellite imagery with elevation, rainfall, soil, population, roads and administrative boundaries. Spatial analysis then reveals patterns, exposure and change through time. It supports watershed management, habitat protection, pollution mapping, environmental-impact assessment and disaster planning.

The two tools are strongest when integrated. Remote sensing supplies timely observations; GIS connects them with field measurements and human information. Ground verification remains important because a remotely sensed signal may have more than one interpretation.

(c) What are Kepler laws related to the motion of planets?

Johannes Kepler formulated three laws that describe planetary motion around the Sun.

1. Law of orbits: Every planet moves in an elliptical orbit with the Sun at one focus. The Sun is therefore not necessarily at the geometrical centre of the orbit. A planet’s distance from the Sun changes between perihelion, its nearest point, and aphelion, its farthest point.
2. Law of areas: A line joining a planet to the Sun sweeps out equal areas in equal intervals of time. To sweep the same area, the planet moves faster when it is near the Sun and more slowly when it is farther away. Its orbital speed is therefore not constant.
3. Law of periods: The square of a planet’s orbital period is proportional to the cube of the semi-major axis of its orbit: T² ∝ a³. For bodies orbiting the same central mass, T²/a³ is constant. Planets with larger orbits consequently require much more time to complete one revolution.

Kepler derived these laws from precise astronomical observations, especially those collected by Tycho Brahe. The laws described how planets move, while Newton’s law of gravitation later explained why. They remain useful for planets, moons, artificial satellites and many other two-body orbital systems.

(d) What is difference between preservatives and antioxidants? Discuss briefly with examples.

Preservatives are substances or processes used to delay food spoilage and extend safe shelf life. The category includes antimicrobial agents that inhibit bacteria, yeasts or moulds, as well as substances that slow chemical or enzymatic deterioration. Salt, sugar, vinegar, sodium benzoate, potassium sorbate and nitrites are familiar examples. Their suitability and permitted concentration depend on the food and applicable safety rules.

Antioxidants specifically slow oxidation. Oxidation can make fats rancid, destroy sensitive vitamins, alter colour and produce undesirable flavours. Antioxidants work by donating electrons or hydrogen, binding metal catalysts, removing oxygen or interrupting free-radical chain reactions. Ascorbic acid, tocopherols, rosemary extract, butylated hydroxyanisole and butylated hydroxytoluene are examples.

The categories overlap. An antioxidant used to delay oxidative spoilage is functioning as a preservative, but not every preservative is an antioxidant. Sodium benzoate mainly restrains microbial growth in acidic foods and is not used chiefly for antioxidant action. Tocopherol mainly protects oils against oxidation and therefore preserves quality through a different mechanism.

The clearest distinction is purpose and mechanism: “preservative” is the broader functional category, while “antioxidant” identifies substances that preserve by controlling oxidation. Neither category makes poor handling safe; hygiene, temperature control and suitable packaging remain essential.