The volume of a warmed part of the air is reduced and its density increases.
Explanation:
In a convective form of heat transfer, the volume of a warmed part of air is not reduced and its density does not increase.
During convection, heat causes the warm part of the air to expand and its volume increases. When volume increases, density is reduced.
- Convection is a form of heat transfer that involves the actual movement of particles of the medium.
- It usually occurs in fluids i.e gases and liquids.
- In convection, the cold part exerts a buoyant force on the warmer air below and causes it to rise.
- As the warmer part is rising the cooler part replaces it and a convective cell is formed in the process.
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Answer:
v=32.9m/s
Explanation:
The acceleration needed to mantain a circular motion of radius r and speed v is given by the equation 
This is the centripetal acceleration. The person will feel what is called a centrifugal acceleration, of the same value, because he is not in an inertial frame (thus subject to fictitious forces, product of inertia).
We want to know the speed of his head when it is subject to 12.5 times the value of the acceleration of gravity while moving on a 8.84m radius circle, so we must do:

The average speed is 20.8 m/s
Explanation:
The average speed for the trip is given by:

where
d is the distance covered
t is the time elapsed
For the trip in this problem, we have:
d = 187 km = 187,000 m is the distance travelled
The initial time is 10:00 pm while the arriving time is 12:30 am: this means that the time elapsed is 2.5 hours. Converting into seconds,

Therefore, the average speed for the trip is

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Answer: William Thomson, better known as Lord Kelvin
The best option is C. This is due to friction.