# Types of Heat Transfer: Convection

#### Academic Questions in PhysicsPlease check out our Test Your Knowledge page to see all Questions and Answers The rate of change of momentum is proportional to the applied force and will take place in the direction of that force. The above statement is attributed to _____. A. Albert Einstein B. Isaac Newton C. Galileo Galilei D. Neils Bohr E. Ernest Rutherford F. Marie Curie The Law of Inertia is also referred to as _____. A. 1st Law of Thermodynamics B. 2nd Law of Thermodynamics C. 3rd Law of Thermodynamics D. Newton's 1st Law of Motion E. Newton's 2nd Law of Motion F. Newton's 3rd Law of Motion The process whereby the velocity of an object increases and decreases over a period of time is best associated with the term _____. A. Speed B. Velocity C. Momentum D. Constant Velocity E. Acceleration F. Average Velocity The rate of motion is best referred to as _____. A. Speed B. Velocity C. Momentum D. Inertia E. Acceleration F. Constant Velocity Consider this expression below: A body X exerts a force FX on another body Y. In return, body Y exert a force FY back on body X. The forces FX and FY are equal in magnitude but opposite in direction. Putting the above expression into equation: FX = -FY Where FX is the action force FY is the reaction Force The above expression relates to _____. A. Theory of Force B. Force Postulate C. Einstein's proposal on Relativity D. Newton's 1st law of motion E. Newton's 2nd law of motion F. Newton's 3rd law of motion The tendency of a body to remain in a state of rest or in uniform motion is referred to as _____. A. Tension B. Uniform acceleration C. Constant acceleration D. Deceleration E. Inertia F. Velocity A change in the position of an object with reference to time is best described as _____. A. Momentum B. Displacement C. Velocity D. Acceleration E. Direction F. Motion The saying 'what goes up on earth must come down' can be best attributed to _____. A. Force B. Motion C. Mass D. Acceleration E. Average velocity F. Constant velocity ### 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.

Below is an explanation on the processes involved in boiling:

• The water molecules inside the pot (yet to be boiled) possesses equal kinetic energy.
• 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.
• 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.

The image below shows the convection current during the process of boiling: 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.

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).

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.

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: 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). 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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