Science

The brain has several types of memory, which can be classified into different categories:

1. Sensory Memory: This is the initial stage of memory where information from the senses (hearing, touch, smell, taste, and vision) is briefly held for a very short duration, typically just a few seconds. Sensory memory is highly detailed but is out of conscious control^[1].

2. Short-term Memory (Working Memory): This type of memory allows individuals to hold and manipulate information for a short period, generally from a few seconds to a minute. It has a limited capacity, often considered to be around 7±2 items, and is closely related to working memory, which emphasizes the active manipulation of information^[1][2][6].

3. Long-term Memory: This storage space is designed to hold information for a longer duration, potentially for years. Long-term memory can be subdivided into two main categories:
   - Explicit Memory (Declarative Memory): This includes memories that require conscious thought, such as recalling facts and events. It can further be broken down into:

   • Episodic Memory: Related to personal experiences and specific events in time and context.
   • Semantic Memory: Encompasses general knowledge about the world and facts^[1][6].
   • Implicit Memory (Non-declarative Memory): This type does not require conscious thought and includes procedural memories, such as skills and tasks learned through repetition (e.g., riding a bike)^[2][6].

Overall, memory involves complex processes that encompass different types and functions, each associated with various brain regions responsible for encoding, storage, and retrieval of information.

Metals have a much higher thermal conductivity than wood. For example, according to one source, common structural softwood lumber (at about 12% moisture content) has a thermal conductivity in the range of 0.7–1.0 Btu·in/(h·ft²·°F), whereas metals such as aluminum and steel have conductivities around 1,500 and 310 Btu·in/(h·ft²·°F) respectively, showing that metals transfer heat far more quickly than wood^[1].

This high thermal conductivity in metals is largely due to their dense atomic structure and the presence of free electrons, which enable rapid heat transfer; in contrast, wood’s complex composition, which includes cellulose and lignin, and its porous structure results in much slower heat transfer^[3][4].

In everyday experience, these differences explain why metal surfaces feel colder than wooden ones at the same temperature—because metal draws heat away from your skin more quickly due to its high thermal conductivity, while wood’s low conductivity means it draws heat away much more slowly^[9].

Furthermore, listing typical values from another source shows that metals like copper and aluminum have thermal conductivities around 400 and 205 W/(m·K) respectively, whereas wood is reported to have values roughly between 0.1 and 0.2 W/(m·K), reinforcing the huge gap between the two types of materials^[7].

When heat leaves the body, specialized nerve endings in the skin—called thermoreceptors—detect this change in temperature. These receptors, which are found in both the epidermis and dermis, monitor the skin’s temperature by directly sensing the energy balance that results when heat is lost via conduction, convection, or radiation^[8][5]

As heat exits the skin, its temperature drops. This cooling causes a change in the cell membrane of thermoreceptors; in particular, temperature-sensitive proteins such as transient receptor potential (TRP) channels respond by altering their ion flow. For instance, some TRP channels are tuned to activate when the skin cools, converting the thermal loss into electrical signals (graded potentials that lead to action potentials) which then travel along nerve fibers to the brain^[8][5]

These electrical signals inform the nervous system about changes in skin temperature. When heat is being lost, cold receptors typically increase their firing rate, alerting the brain that the local temperature has dropped. This information is used not just for the perception of the environment but also to help trigger protective thermoregulatory responses—such as reducing blood flow to the skin (vasoconstriction) or initiating shivering—to conserve body heat^[9][14]

Furthermore, the materials that come in contact with the skin can affect this process. For example, a metal object may feel cooler than a plastic one even at the same temperature because metal conducts heat away from the skin more efficiently, thereby accelerating the rate at which heat is lost and enhancing the cooling sensation^[8][13]

Metal feels colder than wood at the same room temperature because when you touch an object, your skin senses how quickly heat is conducted away rather than the object’s actual temperature^[2]. Metals have a high thermal conductivity due to their densely packed atoms and free electrons that facilitate rapid energy transfer, so heat from your warm skin is quickly drawn away when you touch metal^[9]. In contrast, wood has a porous structure and complex molecular composition that results in much lower thermal conductivity, meaning it does not draw heat away from your skin as quickly, and therefore feels warmer^[6]. This difference in heat transfer explains why, even at the same ambient temperature, metal feels noticeably colder than wood^[7][8].

'How Everything Works' is described as a comprehensive explainer content domain that focuses on breaking down the mechanisms, systems, and principles behind the world around us^[1]. This field covers a wide range of topics, from everyday phenomena like smartphone processes and bread rising, to complex technological systems such as internet routes and internal combustion engines^[1]. The core philosophy is to make complex concepts accessible through clear explanations, visual aids, and relatable analogies, transforming intimidating technical knowledge into understandable insights^[1].

The domain spans multiple disciplines, including technology and engineering (computers, electronics, machinery, infrastructure), natural sciences (human biology, physics, chemistry, earth sciences), everyday phenomena (cooking, sleep, vision, sound), and cutting-edge innovations (artificial intelligence, space technology, renewable energy systems)^[1]. What unites all these topics is a systems-thinking approach, emphasizing the understanding of how individual components interact to create functioning systems, rather than just the components themselves^[1]. The content consistently highlights the elegant mechanisms that make these systems work, such as how the human circulatory system delivers oxygen to cells or how a refrigerator maintains a cold temperature^[1].

This type of content has gained significant popularity in the digital age, with channels like 'How Everything Works' on YouTube amassing millions of subscribers^[1]. This popularity indicates a widespread demand for accessible scientific and technical education, appealing to natural curiosity about the world^[1]. It helps build practical understanding, enables informed decision-making, fosters appreciation for innovation, and connects individuals more deeply to the technologies and processes they encounter daily^[1]. The content bridges the gap between expert knowledge and general understanding, serving both educational purposes and pure intellectual curiosity, making it a cornerstone of lifelong learning and STEM education^[1].