Before a person walks through burning coal, the person will make sure their feet are very wet. When they start walking on the coal, this moisture will evaporate and form a protective gas layer underneath the person's feet. You can see examples of this if you happen to drip some water on a hot stove or any very hot surface. The water will very easily glide around on top of a newly formed layer of air underneath it -- like air hockey pucks on an air hockey table. Note that when someone walks through burning coal, typically this is also done very quickly to prevent a great deal of exposure to possible harm. By walking quickly, thinking positively, and letting the water cushion you from immediate danger over a short distance, such a task is possible. You may have also heard of physics teachers demonstrating how this principle works by sticking their hand first in a bucket of water and then quickly in a bucket of boiling molten lead. In the lead, their hand is protected briefly by a layer of gas from the evaporated water (the water vapor). I'm fairly sure that there is a name for this particular layer of gas, but I'm afraid the name is beyond me at the moment. In other words, water vapor has a low heat capacity and poor thermal conduction. Very often, the coals or wood embers that are used in fire walking also have a low heat capacity. Sweat produced on the bottom of people's feet also helps form a protective water vapor. All of this together makes it possible, if moving quickly enough, to walk across hot coals without getting burned. WARNING: Do not attempt to perform any of the actions described above. You can seriously injure yourself. Answered by: Ted Pavlic, Electrical Engineering Undergrad Student, Ohio St. (citing my source)
The process in which water vapour and carbon dioxide
traps heat is called the “greenhouse effect”.
The greenhouse effect is a natural phenomenon which
occurs every day. To illustrate an example of this natural phenomenon, d<span>uring the day the Sun shines through the atmosphere.
Earth's surface warms up because of the sunlight. Meanwhile at night in the
absence of the sunlight, Earth's surface cools back and releasing the heat back
into the air. However some of the heat is retained by the greenhouse gases
(such as carbon dioxide and water vapour) in the atmosphere. This process what
keeps our planet Earth warm and cozy at an average temperature of 16°C.</span>
<span>
</span>
<span>Answer:</span>
<span>greenhouse effect</span>
1.47x10^5 Joules
The gravitational potential energy will be the mass of the object, multiplied by the height upon which it can drop, multiplied by the local gravitational acceleration. And since it started at the top of a 60.0 meter hill, halfway will be at 30.0 meters. So
500 kg * 30.0 m * 9.8 m/s^2 = 147000 kg*m^2/s^ = 147000 Joules.
Using scientific notation and 3 significant figures gives 1.47x10^5 Joules.
Answer:
750 people
Explanation:
From the question,
Number of people in the city = population density×Area of the city
N = D×A.......................... Equagtion 1
Where N = Number of people in the city, D = population density, A = Area of the city.
Given: D = 50 people per square kilometer, A = 1.5×10 square kilometer.
Substitute into equation 1
N = 50(1.5×10)
N = 750 people.
Hence the total number of people in the city is 750 people.
