Temperature

• You use the words hot and cold to describe temperature.

• Something is hot when its temperature is high.

• When you heat water on a stove, its temperature increases.

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• How are temperature and heat related?

Matter in Motion

• The matter around you is made of tiny particlesatoms and molecules.

• In all materials these particles are in constant, random motion; moving in all directions at different speeds.

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Matter in Motion • The faster they move, the more kinetic

energy they have.

• This figure shows that particles move faster in hot objects than in cooler objects.

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As an object becomes hotter, its particles

move faster.

A thermometer is based on the idea that matter expands when its particles move faster and contracts when they slow down.

If it touches matter with particles that are speeding up, particles in the liquid inside the thermometerspeed up too. They move farther apart.

Measuring Moving Particles(Getting a temperature)

Because the liquid expands more than the glass tube, it moves up the tube. The reading on the number line shows a greater number of degrees. (It’s hotter)

As the object cools, its particles move more slowly

If the particles slow down, the liquid contracts.

The shorter column in the tube shows fewer degrees.

The thermometer must be on or in whatever it’s measuring.

Measuring Moving Particles(Getting a temperature)

Temperature

• The temperature of an object is a measure of the average kinetic energy of the particles in the object.

• As the temperature of an object increases, the average speed of the particles in random motion increases.

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Temperature • In SI units, temperature is measured

in kelvins (K).

• A more commonly used temperature scale is the Celsius scale.

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• One kelvin is the same as one degree Celsius.

Fahrenheit Scale In the United States, the most common temperature scale is called the Fahrenheit scale. On this scale, the number 32 is assigned to the temperature at which water freezes. The number 212 is assigned to the temperature at which water boils. The interval between these two temperatures is divided into 180 equal intervals called degrees Fahrenheit (°F).

Celsius Scale The temperature scale used in most of the world is the Celsius scale.

On this scale, the number 0 is assigned to the temperature at which water freezes. The number 100 is assigned to the temperature at which water boils. The interval between freezing and boiling is divided into 100 equal parts, called degrees Celsius (°C).

Kelvin Scale The temperature scale commonly used in physical science is the

Kelvin scale. Units on the Kelvin scale are the same size as those on the Celsius scale, and are called kelvins (K). Any temperature on the Kelvin scale can be changed to Celsius degrees by subtracting 273 from it. So the freezing point of water on the Kelvin scale is 273 K and the boiling point is 373 K. Why is the number 273 so special? Experiments have led scientists to conclude that –273°C is the lowest temperature possible. At this temperature, called absolute zero, no more energy can be removed from matter. The Kelvin scale is defined so that zero on the Kelvin scale is absolute zero.

Thermal Energy

• If you let cold butter sit at room temperature for a while, it warms and becomes softer.

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• Because the air in the room is at a higher temperature than the butter, particles in air have more kinetic energy than butter particles.

Thermal Energy

• Collisions between particles in butter and particles in air transfer energy from the faster-moving particles in air to the slower-moving butter particles.

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• The butter particles then move faster and the temperature of the butter increases.

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• Because the kinetic energy of the butter particles increased as it warmed, the thermal energy of the butter increased.

Thermal Energy • The sum of the kinetic and potential energy

of all the particles in an object is the thermal energy of the object.

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Thermal Energy and Temperature

• When the temperature of an object increase, the average kinetic energy of the particles in the object increases.

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• Because thermal energy is the total kinetic and potential energy of all the particles in an object, the thermal energy(TEMPERTURE)

of the object increases when the average kinetic energy of its particles increases.

Thermal Energy and Mass • Suppose you have a glass and a beaker of

water that are at the same temperature.

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• The beaker contains twice as much water as the glass.

• The water in both containers is at the same temperature, so the average kinetic energy of the water molecules is the same in both containers.

Thermal Energy and Mass • There are twice as many water molecules in

the beaker as there are in the glass. So the total kinetic energy of all the molecules is twice as large for the water in the beaker.

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Thermal Energy and Mass 6.16.1

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• As a result, the water in the beaker has twice as much thermal energy as the water in the glass does.

• If the temperature doesn’t change, the thermal energy in an object increases if the mass of the object increases.

Temperature