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Heat and Thermodynamics

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A series of free Online High School Physics Video Lessons.

In this lesson, we will learn

  • the second law of thermodynamics
  • entropy
  • internal energy
  • measurement of heat
  • thermal expansion

Second Law of Thermodynamics

The 2nd Law of Thermodynamics can be rephrased in several ways. Fundamentally, it says that heat always flows from hot objects to cold objects (unless work is exerted to make it flow the other direction). It can also be expressed using the concept of entropy as saying that the system's entropy will always naturally increase if no work is exerted to decrease it. These rephrasings mean fundamentally the same thing because heat deals with kinetic energy and increasing a system's kinetic energy will increase the system's entropy.
Understanding and applying the second law of thermodynamics.
Demonstrating the 2nd Law of Thermodynamics in 3 different ways: conduction, radiation, convection


Entropy measures the amount of disorder in a system. Nature tends towards disorder, so as time elapses, entropy naturally increases. Energy is required in order to decrease entropy.
Understanding the concept of entropy.

Internal Energy

An object's internal energy is the kinetic energy from the random motion of the particles within it and the potential energy from movement of electrons in its atoms. Generally internal energy is represented with the letter U.
Understanding the concept of internal energy

Measurement of Heat

Measurement of heat is done in calories. One calorie is the amount of energy required to raise one gram of water one degree Celsius. To measure heat, you multiply the change in temperature of a sample of water by the mass of the water.
What is heat? This lesson discusses heat as the transfer of energy from a hotter area to a cooler area. We also look at how heat is measured, and the difference between calories and Food Calories.
Calories in a peanut are approximated by burning the peanut and capturing the energy in water

How many calories are in a food sample? We can find out by burning a potato chip, causing it to release energy. This will be absorbed by water in a calorimeter, so we will then calculate how much energy the water absorbed, using an equation for heat energy, specific heat, mass, and change in temperature (delta temperature). We will calculate the Calories per gram and Calories per serving, and then calculate percent error to find out how far off out experimental numbers were from the real values.

You might be making one of these common mistakes! In this video, we'll talk about the most common mistakes that people make when they're doing calorimetry problems. Often, they do not get the mass right when they are doing specific heat calculations with water. Also, the mass of water can be determined from its volume. Because of the density of water, 1 mL of water has a mass of 1 g. This can be used with specific heat capacity to determine the change in heat energy, or enthalpy.

Thermal Expansion

Most matter expands when heated and contracts when cooled, a principle called thermal expansion. The average kinetic energy of the particles increases when matter is heated and this increase in motion increases the average distance between its atoms. It is important to note that water does not follow the rule of thermal expansion. Water expands when it freezes because the crystalline structure of ice takes up more space than liquid water.
Understanding and predicting thermal expansion

What happens when a balloon full of air is plunged into a container full of liquid nitrogen?
What happens when a rubber test tube stopper is placed in a pool of liquid nitrogen?
What happens when liquid nitrogen is trapped inside a sealed container?
Thermal Expansion of Aluminum

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