Why does heat rises

Bud P. Buoyancy is the relevant principle here, and Archimedes figured it out thousands of years ago. What is the better wording that you suggest? Since warm cannot rise of its own accord, there is no pulling effect behind it and thus the implied negative pressure. Attic ventilation is an example where you often hear that the warm air rises to exit the upper vents and pulls in its replacement air.

The objective here is to dispel the notion that warm air is leading the way in the process of convection, when in fact it is the cold air that initiates the process. It seems like semantics until you try to calculate the moving forces behind stack effect and find there is no equation for the mythical upward force from the warm air.

Buoyancy is indeed the principle involved and it is the difference in the weigh of warm vs cold air. Allison, well put. I always Allison, well put. Also, I have a link to an excellent photo of a house-shaped hot air balloon.

At the bottom, the pressure difference is reversed positive outside, negative inside. Leaks at both the top and bottom are necessary for air to keep moving. If the top is airtight, the pressure difference at the bottom goes to zero. If the bottom is airtight, the pressure difference at the top goes to zero.

If air leaks out through the top of the house, more warm air rises inside the house to take its place. Great article Allison. I will Great article Allison. I will share it, so some of my green building buddies can read it.

Funny thing about the semantics conversation is that usually when this is brought up, it leaves out the comprehension level of the average home owner. Which is whom I serve. I already see the blank stares on their face when I try to explain air infiltration based on pressure planes and differentials and the stack effect. I disagree. I just finished I disagree. I just finished reading Dr.

But I found the article clear and easy to understand. The pressures at the top will be identical because each will have an identical amount of air above them. As the cold air moves due to the difference in pressure at the bottom it creates a reduced pressure at the top resulting in the warm air being pulled in the replace it. It is obvious that both must move, but the warm air cannot rise by itself and therefore cannot be credited with pulling the cold air in behind it.

Convection is also the movement of air and since it is the increased pressure that determines the direction of that movement, I give credit to the cold air. You have answered 0 of 3 questions correctly and your score is:. Want to add a little wonder to your website? Help spread the wonder of families learning together.

We sent you SMS, for complete subscription please reply. Follow Twitter Instagram Facebook. Does hot air always rise? How does a hot air balloon fly? Why is the air colder at higher altitudes? Wonder What's Next? Try It Out Are you ready to experiment with air? Ask a friend or family member to help you check out the following activities: Want to see for yourself what happens when there are differences in air temperature?

Make sure you get help from an adult friend or family member, and be sure to check the list of needed supplies before you get started. Air pressure can seem like a bit of a mystery. After all, it's not exactly easy to see air, is it? Some simple science experiments can really make things easier to understand, though. Have fun! Are you up for a challenge? If so, then ask an adult friend or family member to help you build your own Mini Flyable Hot Air Balloon with Candles.

This fun science project will require some special materials and a little patience, but we bet you'll have a blast flying your own homemade hot air balloon powered by candles! Did you get it? Test your knowledge. Wonder Words level upper floor force sink hike basement explain experience elevation atmosphere weather absolutely temperature effectively buoyant straightforward counterintuitive Take the Wonder Word Challenge.

Join the Discussion. Doubter Jun 21, So if hot air rises why is it warmer at sea level than at the top of a mountain? Jul 2, May 23, Bre Dec 16, Wow the video on this question is cool lets see if my teacher will let us do it. But if that movable medium starts to absorb heat energy and its molecules start to move around, they will take up a little more space. The effect ripples across the medium—in this example, air—and the result is that the air becomes less dense.

If a medium like air or water becomes less dense, then it rises through the medium. This is basically why air-filled objects like pool toys float on water. So in the case of, say, a room with a wood stove in it, what happens is that the air near the surface of the wood stove absorbs heat through conduction.

The air then becomes less dense and rises through the remaining air and heads towards the ceiling. The colder ceiling encounters the warmer air and some of the moving molecules of the air cause the ceiling molecules to move, and thus the ceiling warms.

So, though colloquially it can be said that in the case of convection, heat rises, what really happens is that the air is heated by conduction. The exchange of heat energy causes the air molecules to move faster, which causes them to move apart from one another and reduce the density.

Colder and denser air falls to the bottom, which has the effect of causing the hotter and less dense air to rise, and the heat is carried away. But the initial actual transfer of heat to the air was caused by conduction. Convection is a secondary process, which does, of course, carry heat from one place in a room to another. Heat is a form of energy, and there are three ways that heat energy is transferred: conduction, radiation, and convection. In case of convection, colloquially one can say that heat rises, but what really happens is that the initial actual transfer of heat is caused by conduction.

This is because convection is a secondary process. In conduction , quickly vibrating molecules come into contact with slowly vibrating ones, and the slower ones speed up. So, if you put your hand in hot water, the vibrations of the molecules of hot water would vibrate the molecules of your hand, thereby speeding them up and heating up your hand.

Convection occurs when you take a heat source and put it in a movable medium, like air or water. In addition, the atmosphere acts like a greenhouse to reflect some of the heat back toward the earth's surface. At higher altitudes it is relatively harder to retain this energy as more heat is lost to space. Sign up for our email newsletter.

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