Higher Tier: explain heating and cooling mechanisms
הוצג| English | משמעות |
|---|---|
| evaporation/ɪˌvæpəˈreɪʃn/ | התאדות |
| shivering/ˈʃɪvərɪŋ/ | רעידות |
What would explain this observation?
- Higher Tier: Sweat left on the skin does not give the same cooling as sweat that evaporates. Explain the energy transfer, not simply the presence of liquid.
Build the model
- Vasodilation increases blood flow through vessels near the skin surface, increasing the transfer of energy from the blood through the skin to the environment under suitable conditions.
- Evaporation 蒸发 of sweat requires energy, which is transferred from the skin and helps cool the body.
- Higher humidity can reduce evaporation, limiting this cooling mechanism.
- evaporation: Change from liquid to gas at a surface, requiring energy transfer.
- shivering 颤抖: Repeated skeletal-muscle contractions involved in warming the body.
Why does sweat evaporation help cool the skin?
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
Evaporation removes the most energetic water molecules and the energy for the phase change comes from the skin, so the skin is cooled. Sweat does not freeze, and circulation continues throughout.
Match each technical term to its precise meaning.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Vasoconstriction reduces blood flow near the skin surface and therefore reduces energy loss there.
- Stopping sweating avoids further evaporative cooling.
- Shivering is repeated skeletal-muscle contraction; increased muscle activity and respiration transfer more energy, helping warm the body.
- Blood is diverted from surface vessels rather than all circulation stopping.
In the lab: Interpret fictional hot/cold scenarios with stated air temperature, airflow or humidity. Predict which transfer changes and justify the mechanism. A teacher-approved wet/dry cloth model can illustrate evaporation at ordinary temperatures, but its heat transfer is not identical to a human body. Do not test dehydration, extreme environments or forced exercise in participants.
Which two habits make the investigation or model in this case more defensible?
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
Work from known quantities
- Known: a safe fictional cloth model loses 3.6 g water by evaporation in 12 min, a mean of 0.30 g per minute.
- A matched humid-air model loses 1.8 g, or 0.15 g per minute.
- The lower mass-loss rate supports reduced evaporation under those model conditions; it does not calculate body temperature without additional energy data.
Your turn: A fictional cloth model loses 2.8 g water in 14 min. Calculate mean evaporation mass rate.
A fictional cloth model loses 2.8 g water in 14 min. Calculate mean evaporation mass rate.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
The result is 0.2 g/min. Known: 2.8 g of water lost in 14 min. Use mean rate = mass / time. Rate = 2.8/14 = 0.2 g per minute. Mass-loss rate is not itself an energy or a core-temperature measurement.
Check the conclusion and its limits
- Shivering does not warm the body mainly by bones rubbing together.
- Evaporation transfers energy even though the remaining sweat may feel cool.
- A cloth mass-loss result measures water loss rather than automatically measuring heat energy or a person’s core temperature.
Not true: Vasoconstriction stops all blood circulation throughout the body. Vasoconstriction narrows surface vessels to reduce heat loss from the skin; blood keeps flowing everywhere, including the skin. Stopping circulation would kill tissue within minutes.
- Vasodilation increases blood flow through vessels near the skin surface, increasing the transfer of energy from the blood through the skin to the environment under suitable conditions.
- Vasoconstriction reduces blood flow near the skin surface and therefore reduces energy loss there.
- Watch for: shivering does not warm the body mainly by bones rubbing together.
Vasoconstriction stops all blood circulation throughout the body.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
Vasoconstriction narrows surface vessels to reduce heat loss from the skin; blood keeps flowing everywhere, including the skin. Stopping circulation would kill tissue within minutes.
Change from liquid to gas at a surface, requiring energy transfer: write the technical term.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
evaporation means Change from liquid to gas at a surface, requiring energy transfer.