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Heat. Chapter 6. What is Temperature?. Temperature - A measure of the average kinetic energy of the particles in an object. All particles are in constant motion (even if they don’t appear to be) The faster the particles are moving, the more kinetic energy they have.
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Heat Chapter 6
What is Temperature? • Temperature- A measure of the average kinetic energy of the particles in an object. • All particles are in constant motion (even if they don’t appear to be) • The faster the particles are moving, the more kinetic energy they have. • The more kinetic energy they have, thehigher the temperature. • Temperature measures the average kinetic energy of the object because individual particles are moving at different velocities and have different kinetic energies.
Measuring Temperature • Using a thermometer- • As a substance’s temperature increases, it’s particles move faster and spread out. There is more space between them, and the substance expands. • Temperature is measured in three ways: • Fahrenheit – Used in the US • Celsius- Used in rest of the world. The freezing point and boiling point of water is separated into 100 even intervals • Kelvin- used in science • 0 K is the lowest temperature called Absolute Zero– all molecular motion stops
Temperature Conversions • Convert 45 oC to oF • Convert 68 oF to oC
Temperature Conversions • Convert 45 oC to K • Convert 32 K to oC
More About Thermal Expansion • Expansion joints in highway bridges • Bridges heat up and expand – this can cause the bridge to break so joints are installed. • Hot air balloons • When the air inside is heated, it expands and becomes less dense. The balloon rises.
Partner Share • What are the 3 units that we can measure temperature in? Which unit is preferred in physics?
What is Heat? • TRANSFERRED THERMAL ENERGY • Thermal Energy- The energy transferred between objects that are at different temperatures. • Energy is always transferred from the higher temperature to the lower temperature. • Stethoscopes “feel” cold because energy is transferred away from your back to the stethoscope.
Thermal energy is transferredTotal kinetic energy of the particles that makes up the substance
3 Ways to Transfer Thermal Energy • Conduction • Thermal Conduction is the transfer of thermal energy from one substance to another substance through direct contact. • Thermal Conductor- Substances that can conduct thermal energy very well. Ex: Iron • Thermal Insulator- Substances that do not conduct thermal energy well. Ex: Plastic
Ways to Transfer Thermal Energy • Convection • The transfer of thermal energy by the movement of a liquid or a gas. • Warm air or liquid rises to the top because it’s less dense (high energy) At the surface, the warm air/liquid cools, condenses, and sinks back to the bottom. • This cycle is called a convection current
Ways to Transfer Thermal Energy • Radiation • The transfer of energy byelectromagnetic waves such as visible light and infrared waves. • This can occur in empty space.
Radiation and the Greenhouse Effect • Earth’s atmosphere acts like the windows of a greenhouse • It allows the sun’s visible light to pass through it. • A greenhouse also traps heat, keeping the inside warm
Partner Share • What is the difference between heat and temperature?
Specific Heat • Specific Heat-The amount of energy needed to change the temperature of 1 kg (or g) of the substance by 1°C • Metal needs less energy to raise the temperature. Water needs more energy – high specific heat. • Heat can’t be measured directly • We need to use a formula. • heat = mass x constant x change in temperature • q = mcp∆t • q = mcp(Tfinal- Tinitial)
Specific Heat Calculations • How many joules does it take to heat 20. g of water from 10.0 to 40.0 oC? • (Cp (water) = 4.184 J/g oC )
Specific Heat Calculations • How much heat is required to heat 75 g of Iron (Cp = 0.444 J/gCo) from 15.5 to 57.0 oC?
Specific Heat Calculations • How many joules does it take to change the temperature of 15 g of water 25oC? (Cp (water)_ = 4.184 J/g oC )
Matter and Heat States of Matter – the physical forms in which a substance can exist. The states of matter depend on the energy of the particles. Gases = high energy – fast moving Liquids = medium energy – slide past each other Solids = low energy – vibrate in place
Changes of State • Change of State A change of a substance from one state of matter to another state of matter. • PHYSICAL CHANGE!!! • Include: melting, freezing, vaporization, condensation • An ice cube that melts and then turns to a gas can be graphed on a temperature vs. energy graph.
Heat and Chemical Changes • Calorimeter-a device that measures heat • When one object transfers thermal energy to another object, the energy of the warmer object is absorbed by the other object. • calorie- food is burned, energy released is transferred to the water, temp change of the water can be measured. • 1 calorie of food =4.184J of energy.