Physics

Types of Heat Transfer: Convection

len Alfred Ajibola - Thu, 26th December, 2019 @ 17:25: PM

Topics in Physics

Derived Units: Similarities and Differences with Fundamental Units Gravity: Interesting facts on Gravity Relative Density of Substances and Specific Gravity Types of Heat Transfer: Conduction Types of Heat Transfer: Convection Types of Heat Transfer: Radiation Physics Scheme of Work, SS1, First Term Physics Scheme of Work, SS1, Second Term Physics Scheme of Work, SS1, Third Term Velocity and Acceleration Newton's Laws of Motion Importance of Gravity What is Density? Density of various Substances Concepts of Force and Motion Motion and Speed Concept of Heat Transfer Concepts of Heat and Temperature Gravity: What is Gravity? Zeroth Law of Thermodynamics - Thermal Equilibrium Fundamental Quantities and Units in Physics


Academic Questions in Physics

Please check out our Test Your Knowledge page to see all Questions and Answers

A natural force that pulls a body towards the center of the earth is termed _____.

  • A. Centripetal force

  • B. Centrifugal force

  • C. Black hole

  • D. Average acceleration

  • E. Gravity

  • F. Momentum

A Greek letter that expresses density is _____.

  • A. Alpha_d

  • B. Beta_d

  • C. Theta_d

  • D. rho

  • E. dho

  • F. dhr

A glass of water has a higher density than an exact glass of oil.

  • A. True

  • B. False

An 🍎 apple 🍎 falling from a tree has an unbalanced force.

  • A. True

  • B. False

Force is a quantity measured in _____.

  • A. Kilogram

  • B. Gravity

  • C. Incandescence

  • D. Meter per second square (ms-1)

  • E. Mole

  • F. Newton

Heat transfer indicates two systems of varying temperatures and will always be transferred from a region with lower temperature to another with higher temperature.

  • A. True

  • B. False

Heat can be created.

  • A. True

  • B. False

Temperature is defined as the measure or ability of an object or substance to transfer heat energy to another object or substance.

  • A. True

  • B. False

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Heat Transfer - Convection:

Convection is a process of transferring heat from one point to another through the movement of fluids.

Please note the following regarding convection:

1. A conductor or metal is NOT involved in convection.

2. Convection explains the transfer of heat in liquids and gases.

3. The boiling process of water occurs through convection.

Please read on the Concept of Heat Transfer here.

Below is an explanation on the processes involved in boiling:

  • The water molecules inside the pot (yet to be boiled) possesses equal kinetic energy.
    Please read on Liquids and their Characteristics here.
  • When placed on a heat medium, for instance, gas cooker; the water molecules closest to the bottom and margins of the pot will begin to move or rotate as a result of heat transfer by conduction from the metallic pot. (This is so because the pot is a metal and a conductor). As a result, the water molecules (closest to the bottom and margins of the pot) becomes hot.
    Please read on Heat Transfer by Conduction here.
  • Due to the "hotness" of the water molecules closest to the bottom and margins of the pot, they expand and become lighter, thus gaining an increased ability to move (due to an increase in their average kinetic energy). As a result of their increased kinetic energy, they move to the top and center of the pot, displacing the water molecules that were initially there to the bottom.

Note: The displacement of water molecules in the above paragraph is as a result of the difference in density of both water molecules. (That is; the density of water molecules closest to the bottom and margins of the pot versus those at the top/center). Those closer to the bottom/margins of the pot are less dense (or lighter) than those at the top/center). This displacement movement of water molecules is sometimes referred to as the convection current.

Please read more on Density and Specific Gravity here.

The image below shows the convection current during the process of boiling:
Heat Transfer by Convection - Len Academy

Note: The water molecules at the top and center of the pot have a higher density since they are farther away from the bottom and margins of the pot. Also, they have a lower kinetic energy when compared to those at the bottom and margins. They are therefore displaced downwards (since they have higher density and lower kinetic energy) by the water molecules at the bottom and margin of the pot which had now moved upwards and inwards.

The above process continues until the entire water molecules attain the same kinetic energy. At this point, thermal equilibrium is said to be achieved.

Please read more on Thermal Equilibrium and Zeroth Law of Thermodynamics here.

If the pot (containing the boiling water) remains on the cooking gas, the increased kinetic energy of the water molecules will eventually lead to the escape of water particles into the atmosphere via translational motion. At this point, the water in the pot reduces until nothing is left. This emptiness (of the pot) is a result of an increased kinetic energy of the "now" gaseous particles. (The water had changed its state from liquid to gas by now).

Please read on Gaseous Particles and their Behavior and Characteristics here.

Note: In a liquid, the heat energy produced by the particles of higher kinetic energy stimulates the liquid particles of lower kinetic energy (to an increased kinetic energy or rotational motion) until equilibrium is achieved.
(Please read on the Concept of Heat Transfer here to better comprehend Translational, Rotational and Vibrational movements in Particles).

It is important to understand that convection is the main method of heat transfer in water and air.

Please read on Heat Transfer through Radiation here.

The process of increasing a room's atmospheric (or air) temperature through the use of a radiator occurs via convection. The image below shows this:

Heat Transfer in Air by Convection - Len Academy

With regards to convection in air particles (using the above diagram); When we put on the heater or hot radiator (assuming it’s on the floor), the kinetic energy of the air particles closest to the heater will become increased.

The particles of this "hot air" move upwards and sideways, mixing with the cooler air in these regions.

The net result of this rising "hot air" is the transfer of heat energy from a higher region to a lower region.

It is important to state that convection is achieved via the translational and rotational movement of matter. (Translational and Rotational movements are involved in gases and liquids respectively); and they result in the transfer of heat energy.

Note: Convection is NOT usually achieved through vibrational movement (present in solids).

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Alfred Ajibola is a Medical Biochemist, a passionate Academician with over 7 years of experience, a Versatile Writer, a Web Developer, a Cisco Certified Network Associate and a Cisco CyberOps Associate.


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Amazing facts in Physics

One quarter of an apple is filled with air and that's why they float in water

Alfred Noble - Len Academy

The Nobel price was named after its founder, Alfred Noble. He is a Swedish, born on October 21, 1833; and was the inventor of dynamite. He was also a a famous scientist and a successful business man.

Glass Ball - Len Academy

Glass balls bounce higher than rubber balls

Every planet has its own unique gravitational force. For instance, Mars has a gravity of 3.711 m/s2 while earth’s gravitational force is 9.807m/s2.

When two metals are put together in space, they will stick together as if they are welded. This phenomenon is called cold welding

The fastest animal on land is cheetah. It can reach a maximum speed of about 113km per hour.


NOTABLE POINTS IN Physics

The earth is governed by the force of gravity and that’s why everything present on it (humans, plants, animals and even air) is always drawn towards it. You will actually need some form of force greater than gravity in order to pull yourself away from the earth.

As an instance, the earth as we know is spherical in shape and held in space. Also, all humans live on a constantly rotating earth and not inside the earth. Since we live on a spherical earth held in space, how come humans are yet to fall off the constantly rotating earth?

Well, the answer is gravity. Even if we attempt to jump off the earth into space, the force of gravity present on earth will still pull us down. In fact, in order to leave the earth; there has to be a force stronger that gravity; which must be applied to whatever is attempting to leave the earth. For this reason:

Whenever one jumps, a certain amount of force is needed to be applied by that person. However, gravity still return the person back to earth because the applied force had been exhausted.

Please read more on the concept of gravity here.

The larger the size of an object, the greater it’s force of gravity. Gravity is therefore affected by the size and closeness of objects.

Since the earth is larger than the moon, it will have a greater gravitational force than the moon. We will be more attracted on the earth than we would on the moon if we were astronauts on the moon. This implies that we will weigh differently on both places. For this reason, our weight will also vary on the various planets (because they are of different sizes). This is shown in the diagram below:

Weights on planets - Len Academy

Weight depends on the degree at which the gravity on earth or moon or another planet pulls an object while the Mass of any object or body will always remain the same (constant) since it’s the amount or quantity of matter in the body.

Please read on mass versus weight here

Zeroth Law - Len Academy

To better understand the Zeroth Law of Thermodynamics, we need to know what thermal equilibrium is. This is explained below:

Two bodies A and B are said to be in thermal equilibrium if each body can transfer heat to each other when placed closed together but ended up not transferring any heat to each other.

This will mean that both bodies are at equal temperature.

Now, according to the zeroth law, assuming we have three bodies namely X, Y and Z:

If X = Y and Z = Y, then X = Z

From the above expression, it will be observed that: if X and Y are in thermal equilibrium and Z and Y are in thermal equilibrium, therefore, X and Z must be in thermal equilibrium too.

So we can see that according to the zeroth law, temperature is a quantity worth measuring.

It can therefore be said that temperature is the quantity that remains constant (the same) for all systems in thermal equilibrium.

Consequently, the zeroth law of Thermodynamics states that if two separate bodies are in thermal equilibrium with another body, then they are also in equilibrium with each other

Please read more on the zeroth law of thermodynamics here

Fundamental units are the units of fundamental quantities.

A fundamental unit is a unit that does not depend on any other unit; neither can it be changed nor is related to another fundamental unit.

A fundamental unit is also referred to as a basic unit.

Fundamental Units are always constant. This means that they don't change, (remains the same) and are standardized all over the world.

The fundamental quantities alongside their respective fundamental units are 7 in number. They include:

  1. Mass (m) is a fundamental quantity whose unit is kilogram (kg)

  2. Length (l) is a fundamental quantity whose unit is meter, (m)

  3. Time (t) is a fundamental quantity whose unit is second (s)

  4. Temperature (T) is a fundamental quantity whose unit is Kelvin (k)
    You can read on the Concept of Temperature and Heat here.

  5. Electric Current (I) is a fundamental quantity whose unit is ampere (A)

  6. Amount of Substance (n) is a fundamental quantity whose unit is mole (mol)

  7. Luminous Intensity (|v) is a fundamental quantity whose unit is candela (cd)

Please read more on fundamental units here

The classical mechanics (laws of motion) is a fundamental part of Physics.

Below are the Newton's laws of motion:

An object at rest will continue in its state of rest; while an object in uniform motion will continue in a straight line, unless an external force acts on it.

Newton's first law of motion.

Please read on motion and speed here.

The rate of change of momemtum is proportional to the applied force and will take place in the direction of that force.

Newton's second law of motion.

To every action, there is an equal and opposite reaction.

Newton's third law of motion.

Please read on Newton's laws of motion here.