# Heat and Energy Chapter 3 section 2

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Heat and Energy Chapter 3 section 2
Key Concept: Heat flows in a predictable way from warmer objects to cooler objects until all the objects are the same temperature.

What You Will Learn Temperature is a measure of the average kinetic energy of particles in an object. Heat is energy that is transferred between objects. Heat flows by conduction, convection, and radiation.

What is temperature? Temperature is a measure of the average kinetic energy of the particles in an object. All matter is made up of constantly moving particles, such as atoms or molecules. When a particle is in motion, it has kinetic energy.

The faster particles move, the more kinetic energy they have.
The temperature of a substance depends on the kinetic energy of all of its particles. The more kinetic energy the particles have, the higher the temperature of the substance.

The substance on the right has a higher temperature because its particles have a higher average kinetic energy.

Particles in a substance move at random and at different speeds.
The average of all these speeds is the average kinetic energy. When you measure temperature, you are measuring average kinetic energy.

Temperature does not depend on the amount of particles in a substance.
A teapot holds more tea than a tea cup. But if the atoms of tea in both containers have the same kinetic energy, then the tea in both containers has the same temperature.

Thermal Expantion When particles move faster, they move apart.
As the space between the particles increases, the substance expands. Therefore, an increase in temperature leads to an increase in volume. This is called thermal expansion.

What is heat? Heat is the energy that is transferred between objects that are at different temperatures. Heat energy is always passed from an object with a higher temperature to one with a lower temperature. When you touch something hot, heat flows from the object to your finger.

Thermal energy is the total kinetic energy of the particles that make up a substance.
Thermal energy, which is expressed in joules (J), depends partly on temperature. Something at a high temperature has more thermal energy than something at a low temperature.

Thermal energy also depends on the amount of particles in a substance.
The more particles in a substance at a given temperature, the greater the thermal energy.

When things that have different temperatures come into contact, energy will always be transferred.
Energy will pass from the warmer to the cooler object until both have the same temperature. Ex: Hot soup makes cool bowl hot.

How is heat transferred?

The transfer of heat from one object to another through direct contact is called conduction.
Heat flows from the particles of hot soup to the part of the spoon that is in the soup. Heat travels from particle to particle, from the soup all the way up the spoon’s handle.

The transfer of heat due to the movement of matter is called convection.
When you boil water, heat is passed from the burner to the pot and from the pot to the water by conduction. As the water is heated, it becomes less dense.

Cooler, denser water at the top of the pot sinks.
This forces the warmer water to the surface. Water continues to rise and fall in a circular pattern called a convection current.

The transfer of heat or other energy as electromagnetic waves, such as visible light or infrared waves, is called radiation. Radiation can occur between objects that are not in direct contact with each other. The sun transfers energy through space by radiation.

States of Matter The states of matter are the physical forms in which a substance can exist. The three states of matter are solid, liquid, and gas. A substance’s state depends on the speed of its particles, the attraction between them, and the pressure around them

A substance’s chemical composition also influences the state it is in at a given temperature.
For example, milk is a liquid at room temperature, but butter is a solid. A change of state occurs when a substance changes from one state of matter to another.

Changes of state include:
condensing (gas to liquid) freezing (liquid to solid) melting (solid to liquid) evaporating (liquid to gas)

A change of state involves a transfer of heat from one substance to another.
When a substance melts or boils, it gains energy. When a substance condenses or freezes, it loses energy.