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## MCAT

### Course: MCAT>Unit 5

Lesson 11: Principles of bioenergetics

# Heat transfer

Learn how energy moves from warmer to cooler objects, like your hand to a glass of water. Dive into the difference between heat and temperature, and explore how heat transfer shapes our everyday experiences. Created by Jasmine Rana.

## Want to join the conversation?

• heat is defined as the energy that is caused by the random motion of molecules..............then why does heat flow from a hot object to a cold one, and why not randomly from any object to any object?
• So I think you may mixed up your definitions there. Absolute temperature (T) is defined as being proportional to the average translational kinetic energy of the particles (its random motion). That is to say, the hotter something is, the faster the molecules are vibrating, stretching, bending, and moving.

Heat (Q), however, is the transfer of energy due to a difference in temperature. So an object cannot "have" heat. It is one of two ways you can transfer energy between the system and the surroundings. The other is work (W), which is mechanical transfer of energy, and that relationship is described by the First Law of Thermodynamics: delta(U) = Q - W(by the system), where U is internal energy.

When we are talking about heat, we are looking at it more macroscopically rather than the individual motions of the molecules. But this is akin to thinking about why ions travel down their concentration gradient as opposed to some up and some down its gradient. It is driven by entropy and the Second Law, which states that heat flows from higher to lower temperatures.
• At she mentions the heat transferral of your e to some of the water's. Is this convection,conduction or radiation?Thanks
• Conduction and convection.
Your the glass conducts energy from your hand to the water. Convection of water transfers heat throughout the glass
• At what exactly is the (q) that physical scientists use.
• Q is measured in joules and is a measurement for heat energy. For example, (and these numbers are not accurate) let's say in order to bring the water to 37 C, 2000 J of energy must be transferred from the hand to the water. The 2000 J is the variable q.
• does steady state means thermal equilibrium? what are the differences and similarities? pls explain the concept of steady state. I wonder why the temperature gradient stay constant at steady state, isn't it the object will finally have same temperature at all points and there is no temperature gradient?
• Steady state is a more general concept that describes a process that is unchanging over time. It can describe a number of things. I have often heard it used to describe a chemical reaction where the forward and the reverse reaction are equal.

The difference between steady state and thermal equilibrium is that a steady state can include heat being generated. If you held the water long enough eventually it would be the same temperature as your skin. You would not be at thermal equilibrium with the water. Thermal equilibrium can only occur when no new heat is being generated. In order to be at thermal equilibrium you would have to be a corpse holding the water in your cold lifeless hand.
• At first, the video says that you (at 37 Celsius) are holding a cup of water (at 20 Celsius). Wouldn't heat transfer average out those temperatures? I thought that after time, both you and the glass are going to have 28.5 Celsius in temperature. (The average of 37 and 20) However, 28.5 Celsius is extremely low for a human's body temperature. I am very confused.
(1 vote)
• There are two factors you are overlooking.

First factor:
By this logic, if you put an drop of ice water (at 0°C) into a glass of room temperature (say 20°C) water, the final temperature should be about 10°C.

Does that seem reasonable?

How about if you put that same drop of ice water into a swimming pool?

Your prediction would still be that the final temperature is 10°C!?

Second factor:

What happens when you start to feel cold?

What does that process do?

In general, mammals maintain a relatively constant body temperature — this is an example of homeostasis. So unless you are dead, extremely sick, or suffering from hypothermia your body will automatically expend energy to maintain your temperature.

Does this help?
• What are the applications of Thermal Radiation?
(1 vote)
• Wait, what was the system and what was the surrounding. I am confused. Was the surrounding the air around the thing she was holding or the surrounding of the cup?
(1 vote)
• She said the system is the person's hand and the surrounding is the cup of water.
(1 vote)
• Which will cool quicker, a kettle at 100 degrees or kettle at 70 degrees?
(1 vote)
• Hey There,
I have a question hope to get an answer for it.
(Q) Whats the relationship between geometry and heat transfer..?