Đề ôn thi Đề thi vào lớp 10 Trường Phổ thông Năng khiếu môn Tiếng Anh - Mã đề PTNK-175

Have you ever wondered how a simple axe can (21) __________ a thick log of wood into two pieces? The answer lies in one of the six classical simple machines: the wedge. A wedge is essentially two inclined planes joined together to form a sharp edge. This simple tool is designed to separate two objects, or portions of an object, by applying force. It’s a fundamental concept in engineering that we see in many everyday items.

The magic of the wedge works by converting a force applied to its wide end into much larger forces perpendicular to its inclined surfaces. When you strike an axe, (22) __________ force travels down to the sharp edge. This concentrates all the pressure onto a very small area. (23) __________, the wood cannot resist this immense pressure and begins to split apart. The sharper and thinner the wedge, the less effort is needed to do the work.

A common example that doesn't involve cutting is the doorstop. A doorstop is a wedge used (24) __________ a door open or prevent it from moving. When you push a doorstop under a door, friction is created between the door, the floor, and the wedge itself. This friction builds up and creates a strong holding force. Unlike an axe, its primary purpose isn't to separate things permanently, but to hold them securely in place.

An engineer once explained that a wedge's effectiveness depended on its angle. He said that a sharper, narrower angle requires less input force, which really hits the nail on the head when you're designing tools for efficiency. From the sharp point of a nail to the thin blade of a knife, the principle is the same: the angle determines the mechanical advantage you get from the tool.

Understanding this principle allows for better tool design. For example, if a doorstop were wider, it would require more force to push it into place, but it might hold the door more firmly once there. This trade-off between ease of use and holding power is a key consideration for engineers. Wedges are simple, yet powerful, demonstrating how basic physics can be used to accomplish great tasks.

Cities are bustling hubs, often characterized by towering buildings and dense populations. Yet, nestled within this urban sprawl are essential pockets of nature: urban green spaces. More than just a patch of grass or a few trees, these areas, often referred to as a city's "green lungs," are vital for the well-being of both the environment and its inhabitants. From sprawling parks to community gardens, these green havens offer a crucial antidote to the concrete jungle, providing essential environmental services and fostering healthier communities. [I]

Globally, urban planners recognize that these verdant spaces are indispensable. Trees and plants within parks act as natural air filters, absorbing pollutants and releasing oxygen, significantly improving air quality. They also help combat the "urban heat island effect" by providing shade and cooling the environment, making cities more comfortable. Furthermore, green spaces are critical for preserving biodiversity, offering crucial habitats for local wildlife, thereby contributing to a city’s ecological balance and resilience against climate change. [II]

The importance of green spaces resonates particularly strongly in densely populated cities like Ho Chi Minh City. As urban areas expand rapidly, the premium placed on natural surroundings becomes evident. Major new developments, such as Vinhomes Central Park, have strategically leveraged the appeal of their large green areas situated beside the serene Saigon River. These meticulously designed parks are not just an aesthetic addition but a core selling point, attracting residents seeking a balance between modern urban living and access to nature. [III]

For teenagers, these urban oases offer tangible, everyday benefits. Where do you go to unwind after school or meet up with friends on a weekend? Often, it's a local park or green area. These spaces serve as vital social hubs, providing safe, open environments for recreation and social interaction away from screens. Beyond social connections, spending time in nature has profound positive effects on mental health, reducing stress and anxiety, improving mood, and boosting cognitive function. These hidden benefits contribute significantly to overall well-being. [IV]

In conclusion, urban green spaces are far more than mere decorative elements; they are fundamental components of a thriving city. They are the air purifiers, the cooling systems, the biodiversity havens, and the social gathering points that make urban life sustainable and enjoyable. As cities continue to grow, the deliberate creation and preservation of these "green lungs" will be paramount. Investing in parks and gardens means investing in cleaner air, healthier citizens, and more resilient, livable urban environments for everyone.