Question

Annotate: Summarize for each paragraph - write down brief notes or highlight words that are important. As you read -what questions do you ask yourself? What words would you underline? What comments would you make?

Write down the candle's ignition steps?
1.A candle’s flame heats air near the wick

2. ..............................................................

3. ...............................................................

4. ...............................................................

5. ...............................................................

6. .................................................................

Physics of Scale: How Are Candle Flames, Lake Flow,
and Continental Drift Related?

by Professor Andrew Spakowitz

(1) Our everyday experiences offer us innumerable opportunities to observe how physical

forces lead to unexpected and intriguing phenomena. The foundational principles
that govern our physical world are developed to a point where we are able to establish
connections between seemingly disparate observations. Such connections serve to
strengthen our fundamental understanding of nature and provide a roadmap for
predicting the behavior in other areas where our basic understanding has not been
established. In this regard, there is value in stepping away from those problems that
have immediate or personal significance to consider the range of related problems that
may inform us of basic governing principles.

(2) While watching a candle flame, for example, you may be mesmerized by the natural

beauty of the glow and the dancing flicker of the flame. Upon closer inspection, you
may notice that the air within the flame forms a smooth jet near the wick, and farther
above the wick, the flow pattern breaks down into a chaotic, swirling pattern that
causes the flame to flicker. The air rises above the flame. You can move your hand next
to it without being burned, but placing your hand above would be painful. Tilting the

candle leads to the flame reorienting itself in the direction away from the floor.
(3) All of these observations point

to physical principles that are responsible for the behavior of the candle. The fact that the
flame always orients away from the floor and that the hot air rises above the flame suggests that gravity is a critical
contributor. You are probably familiar with the experience of pushing a ball below the surface

of pool water, leading to the ball pushing back against your hand. The air within the
ball has a lower density (or mass per volume of the ball) than the water in the pool.
Therefore, the gravitational force on the air is smaller than the force on the water,
Since the ball is displacing the water, there is a net physical force that drives the ball
upward to replace the volume of air with water. This same effect causes a hot-air
balloon to rise, but in this case, the higher temperature air within the balloon has a

lower density than the cooler air surrounding the balloon.

(4) A candle flame heats up the air near the wick, which reduces the density of that air

relative to the density of the surrounding air. In this regard, the candle flame is akin
to a hot-air balloon without the balloon. The hot air in the flame rises, and cooler air
above and to the sides of the flame circulates downward and back into the flame. This
spontaneous flow pattern results in the hot air that rises being replenished with cooler
air, and the candle continues to burn.

Answer 1