Omar Khalid
Metal and plastic are two materials that are commonly used in everyday objects, from food and beverage containers to electronic devices. One notable difference between these materials is their thermal properties, specifically their ability to radiate cold. This topic explores the question: does metal radiate cold faster than plastic? Understanding the answer to this question provides insight into why certain materials feel colder to the touch, even when they are at the same temperature, and has implications for various applications, such as choosing the best materials for thermal insulation or heat transfer.
| Characteristics | Values |
|---|---|
| Metal's thermal conductivity | High |
| Plastic's thermal conductivity | Low |
| Metal's thermal conductivity (in W/(m/K)) | 205 |
| Plastic's thermal conductivity (in W/(m/K)) | N/A |
| Metal's thermal conductivity compared to plastic | Higher |
| Metal's response to a change in temperature | Quick |
| Plastic's response to a change in temperature | Slow |
| Metal's ability to radiate cold | High |
| Plastic's ability to radiate cold | Low |
| Metal's ability to feel cold | High |
| Plastic's ability to feel cold | Low |
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What You'll Learn
Metal has a higher thermal conductivity than plastic
The thermal conductivity of a material expresses the amount of power transferred per unit of distance per degree of temperature. In the MKS system, the units are Watts per meter Kelvin or W/(m/K). Aluminium, a metal commonly used for beverage cans, has a thermal conductivity of 205 W/(m/K), which is substantially higher than any plastic material currently being produced.
The difference in thermal conductivity between metal and plastic is due to the fact that metal is a conductor, while plastic is an insulator. When you touch an insulator, the heat from your hand has nowhere to go, so you feel it on the spot you touch. However, when you touch a conductor like metal, the heat is distributed evenly throughout the medium, and it doesn't feel as hot because the warmth from your hand is easily dissipated into the air.
The higher thermal conductivity of metal also has implications for beverage containers. Metal cans cool down faster in a refrigerator due to the rapid transfer of hot and cold air between the warmer can and the cool surrounding air. On the other hand, when a metal can is placed in direct sunlight, it will heat up extremely fast compared to a plastic bottle that restricts the energy transfer from the hot air to the liquid.
The thermal properties of both metal and plastic can be harnessed in reusable beverage containers like thermoses, making them effective temperature regulators.
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Metal feels colder to touch than plastic
Metal feels colder to the touch than plastic because it has a higher thermal conductivity. This means that metal draws heat away from our hands faster than plastic, making us feel that the metal is colder than the plastic.
Thermal conductivity is the measurement of the amount of power transferred per unit of distance per degree of temperature. In the MKS system, the units are Watts per meter Kelvin or W/(m/K). Metals generally exhibit high thermal conductivities and are much quicker to respond to changes in temperature in their surrounding environment compared to plastics or foams. For example, aluminium, which is used in most metal cans, has a thermal conductivity of 205 W/(m/K), which is substantially higher than any plastic material currently being produced.
Metals are excellent conductors of heat due to the loosely bound electrons on their atoms, which will readily vibrate and move under a heat source’s influence. This same structural feature gives metal its high thermal conductivity as the free-moving electrons can more easily distribute thermal energy throughout the material.
On the other hand, plastic is classified as an insulator and is extremely slow to respond to changes in the surrounding temperature. When you touch a piece of plastic, your hand heats the plastic right near the surface a bit, and you feel a temperature somewhere between your body temperature and the average plastic temperature.
The difference in thermal conductivity between plastic and metal can be observed in their ability to keep drinks cool. Metal cans will cool down faster when placed in a refrigerator due to the rapid transfer of hot and cold air between the warmer metal can and the cool surrounding air in the fridge. However, when a metal can is placed in direct sunlight, it will begin to heat up extremely fast compared to a plastic bottle that restricts the energy transfer from the hot air to the liquid.
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Metal cools down faster than plastic in a refrigerator
Aluminum, the metal used in most metal cans, has a thermal conductivity of 205 W/(m/K), which is substantially higher than any plastic material currently being produced. Plastic, on the other hand, has a thermal conductivity of around 0.02 to 0.05 W/(m/K). This means that aluminum transfers a hundred thousand times more heat per unit of distance than plastic at the same temperature.
The high thermal conductivity of metal cans allows for a faster and more effective heat transfer between the cold fridge air and the warmer beverage inside. In a confined space like a refrigerator, air currents are less of a factor in temperature control, so the elevated thermal conductivity of metal becomes a more significant factor in cooling objects down.
However, it is worth noting that while metal cools down faster than plastic in a refrigerator, liquids in metal containers may not stay cold for longer. Experiments suggest that the liquids in metal and plastic containers stay cold for about the same duration. This is because the only way to restrict energy and heat flow is to isolate a material from its surrounding environment. In a vacuum, there are fewer surrounding molecules for the fast-moving atoms of the hot material to bump into, so it will retain its energy and stay hotter for longer.
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Plastic bottles warm faster than opaque metal containers in direct sunlight
Metal has a higher thermal conductivity than plastic, meaning it can transfer heat faster. This is due to the loosely bound electrons on their atoms, which will readily vibrate and move under a heat source’s influence. This is why a metal plate "feels colder" than a plastic plate—the metal draws heat away from your hand faster.
However, when it comes to drinks in plastic bottles versus metal cans, the situation is more complex. Metal cans cool down faster in a refrigerator due to the rapid transfer of hot and cold air. But when placed in direct sunlight, metal cans will begin to heat up extremely fast compared to plastic bottles, which restrict the energy transfer from the hot air to the liquid. This is because the plastic bottle acts as a lens and magnifies the sunlight, warming the liquid inside faster than in an opaque metal container.
Therefore, if you want to keep a drink cold when outside in direct sunlight, an opaque metal container is a better choice than a clear plastic bottle. The metal will warm up faster in the sun, but the plastic bottle will transfer this heat to the liquid inside faster due to the lens effect. However, if you are keeping drinks in a confined space like an ice chest, metal cans are the best option as air currents are less of a factor, and the higher thermal conductivity of metal allows for faster and more effective heat transfer.
It is worth noting that plastic bottles can also have negative environmental impacts and may release harmful chemicals when exposed to high temperatures or sunlight. For this reason, it is generally recommended to use a reusable metal water bottle instead of a plastic one.
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Metal draws heat from the human body faster than plastic
The rate of heat transfer is much faster in metal than in plastic. So, you lose more heat when you touch metal, which makes it feel colder. Some materials can ""steal"" heat from you faster and transfer that heat to the rest of the object. Metal is one such material. Plastic, on the other hand, is a good insulator, meaning it steals heat more slowly.
This phenomenon can be observed in a social experiment conducted by the YouTube channel Vertasium, in which ice melts faster on a steel plate than a plastic plate, even though the steel plate "feels colder". This is because the steel plate gives away heat to the ice block faster than a plastic block.
Metals are excellent conductors of heat due to their loosely bound electrons, which will readily vibrate and move under a heat source's influence. This structural feature gives metal its high thermal conductivity as the free-moving electrons can more easily distribute thermal energy throughout the material.
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Frequently asked questions
Metal generally has a higher thermal conductivity than plastic, meaning it can conduct heat faster. This is why metal feels colder to touch than plastic.
Metal is a good conductor of heat, meaning it can easily transfer heat to colder objects or absorb heat from warmer objects. When you touch a piece of metal, your fingers rapidly lose heat, and the metal feels cold. Plastic, on the other hand, is an insulator, meaning it does not transfer heat as easily.
Metal cans cool down faster in a refrigerator due to the rapid transfer of hot and cold air. However, in direct sunlight, a metal can will heat up extremely fast compared to a plastic bottle. Plastic bottles in direct sunlight allow UV rays to permeate through and reach the liquid inside, warming the liquid faster than in an opaque metal container.
