Define one calorie

Answer

**Step-by-Step Solution:**

1. **Understanding the Concept of Calorie**:
- The term "calorie" is a unit of measurement used to quantify heat energy.

2. **Defining the Conditions**:
- To define one calorie, we need to specify the conditions under which it is measured.
- The definition states that it is measured at a pressure of 1 atmosphere.

3. **Identifying the Substance**:
- The substance involved in this definition is water, specifically 1 gram of water.

4. **Temperature Change**:
- The definition specifies that the temperature change is 1 degree Celsius (or 1 degree centigrade).

5. **Putting It All Together**:
- Therefore, one calorie is defined as the amount of heat required to raise the temperature of 1 gram of water by 1 degree Celsius at a pressure of 1 atmosphere.

**Final Definition**:
One calorie is the amount of heat required to raise the temperature of 1 gram of water by 1 degree Celsius at a pressure of 1 atmosphere.

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