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A Closer Look

Goose Bumps and Shivering
or an average age and minimal level Contraction of a tiny muscle attached to core to be conducted through the skin, then
Fof activity, many people feel comfort- the base of the hair shaft makes a tiny knot, radiated away. It also causes some people to
able when the environmental temperature or bump, on the skin. These are sometimes have a red blush from the increased blood
is about 25°C (77°F). Comfort at this tem- called “goose bumps” or “chill bumps.” flow in the skin. This action increases con-
perature probably comes from the fact that Although goose bumps do not significantly duction through the skin, but radiation
the body does not have to make an effort to increase insulation in humans, the equiva- alone provides insufficient cooling at envi-
conserve or get rid of heat. lent response in birds and many mammals ronmental temperatures above about 29°C
Changes that conserve heat in the body elevates feathers or hairs and greatly enhances (84°F). At about this temperature, sweating
occur when the temperature of the air and insulation. begins and perspiration pours onto the skin
clothing directly next to a person becomes Further cooling after the blood vessels to provide cooling through evaporation. The
less than 20°C or if the body senses rapid in the skin have been constricted results warmer the environmental temperature,
heat loss. First, blood vessels in the skin are in the body taking yet another action. The the greater the rate of sweating and cooling
constricted. This slows the flow of blood body now begins to produce more heat, through evaporation.
near the surface, which reduces heat loss making up for heat loss through involun- The actual responses to a cool, cold,
by conduction. Constriction of skin blood tary muscle contractions called shivering. warm, or hot environment are influenced
vessels reduces body heat loss but may also The greater the need for more body heat, by a person’s activity level, age, and gender,
cause the skin and limbs to become signifi- the greater the activity of shivering. and environmental factors such as relative
cantly cooler than the body core tempera- If the environmental temperatures rise humidity, air movement, and combinations
ture (producing cold feet, for example). above about 25°C (77°F), the body triggers of these factors. Temperature is the single
Sudden heat loss, or a chill, often initi- responses that cause it to lose heat. One most important comfort factor. But when
ates another heat-saving action by the body. response is to make blood vessels in the the temperature is high enough to require
Skin hair is pulled upright, erected to slow skin larger, which increases blood flow in perspiration for cooling, humidity becomes
heat loss to cold air moving across the skin. the skin. This brings more heat from the an important factor in human comfort.

meteor enters Earth’s atmosphere and is heated so much from
4.3 HEAT
the compression that it begins to glow, resulting in the fi reball
Suppose you have a bowl of hot soup or a cup of hot coff ee that and smoke trail of a “falling star.”
is too hot. What can you do to cool it? You can blow across the To distinguish between the energy of the object and the
surface, which speeds evaporation and therefore results in cool- energy of its molecules, we use the terms external and internal
ing, but this is a slow process. If you were in a hurry, you would
probably add something cooler, such as ice. Adding a cooler
substance will cool the hot liquid.

You know what happens when you mix fluids or objects
with a higher temperature with fluids or objects with a lower

temperature. The warmer-temperature object becomes cooler,

and the cooler-temperature object becomes warmer. Eventually, Molecule is pulled
both will have a temperature somewhere between the warmer from home position,
stretching bonds

and the cooler. This might suggest that something is moving
between the warmer and cooler objects, changing the tempera-
ture. What is doing the moving?

The relationship that exists between energy and tempera-
Molecule is pulled
ture will help explain the concept of heat, so we will consider
back, gaining
it first. If you rub your hands together a few times, they will vibrational kinetic

feel a little warmer. If you rub them together vigorously for a energy
while, they will feel a lot warmer, maybe hot. A temperature
increase takes place anytime mechanical energy causes one

surface to rub against another (Figure 4.8). The two surfaces
FIGURE 4.8 Here is how friction results in increased tem-
could be solids, such as the two blocks, but they can also be
peratures: Molecules on one moving surface will catch on another

the surface of a solid and a fluid, such as air. A solid object surface, stretching the molecular forces that are holding it. They
moving through the air encounters air compression, which are pulled back to their home position with a snap, resulting in a
results in a higher temperature of the surface. A high-velocity gain of vibrational kinetic energy.
92 CHAPTER 4 Heat and Temperature 4-8