Temperature Section 2

Temperature What is the temperature today? Is it hot or cold outside, do you need a jacket? Hot and cold are everyday terms used to describe temperature, but those terms are not scientific. While you may think it is cold in the classroom, someone else may think it is comfortable or even too hot!

Temperature and Kinetic Energy Remember that everything is made of atoms which are in constant motion, even when they appear to be still Even objects such as your desk and your pencil, which seem to be still, have atoms that are moving around at all times Those atoms do not move in one direction, but tend to bounce around The atoms in gases can bounce around more than the atoms in a liquid The atoms in solids just kind of move back and forth

Temperature and Kinetic Energy Temperature is the measurement of the average kinetic energy of the atoms in an object When an objects temperature is higher, it has more kinetic energy As temperature increases, the objects atoms move faster, which means they have more kinetic energy.

Measuring Temperature Some people may say the temperature of the water in a swimming pool is cold, while others say it is warm This is why temperature can’t be accurately described by how it feels Since temperature is the measure of how much energy the atoms of an object has, you may think you need to measure the atoms themselves

Measuring Temperature However, atoms are so small that even a tiny piece of material has trillions of atoms in it There is no practical way to measure the energy of an atom So what is a scientist to do? One practical way of measuring temperature is to use a thermometer

The Fahrenheit Scale The temperature scale you should be most familiar with is the Fahrenheit scale. On the Fahrenheit scale, the freezing point of water is 32◦F and the boiling point of water is 212◦F The space between the freezing point and boiling point is evenly divided between into 180◦ This scale is mainly used in the USA.

The Celsius Scale Another temperature scale that is more widely used is the Celsius scale On the Celsius scale, the freezing point of water is 0◦F and the boiling point of water is 100◦F Because there are fewer degrees between those points on the Celsius scale, the temperature change between degrees is greater on the Celsius scale than on the Fahrenheit scale.

Heat On a warm day, you can feel the suns heat on you, in the winter, you can feel the heat of a fire on your cold hands In both cases, you could feel the heat making you warmer If you pick up a glass of iced tea and hold it, the drink will warm up while your hand gets colder This because your hand has more kinetic energy

Heat Kinetic energy from your hand is transferred to the drink when the atoms in your hand collide with the atoms in your drink A transfer of energy from one object to another due to a difference in temperature is called heat Heat flows from warmer object to cooler ones The heat from your hand will continue to flow into the drink until your hand and the drink are the same temperature

Heat and Temperature How much does the temperature of an object increase when heat is transferred to it? It depends on the object The more mass the object has, usually, the more heat it will take to raise its temperature Water is strange though, it takes an unusual amount of heat to raise the temperature of water one degree For this reason, water is often used as a coolant in cars

Lakes and Air Temperature How does the temperature of a lake compare to the temperature of the surrounding air on a hot summer day? If you have been swimming in a lake, you may have noticed that the water seems cooler than the air. Remember that water absorbs lots of energy before it begins to heat up Therefore large bodies of water heat up and cool down slower than the surrounding air Therefore, a lake will be cooler in the summer, and warmer in the winter!

Heat on the Move A transfer of energy occurs if there is a difference in temperature between two object on contact The can happen in three ways: radiation, conduction, and convection Conduction transfers heat through solids and liquids Convection transfers heat through liquids and gases Radiation transfers heat through space

Conductors Materials that make it easy to transfer energy are called thermal conductors Most metals are good conductors of heat Metals such as gold, silver, and copper are the best conductors Copper is widely available and often used in cooking pans. While much of the pan may be made of steel, they sometimes have a copper bottom because copper spreads heat more evenly

Insulators Materials that do not transfer heat well are called thermal insulators When you are cold, you may put on a sweater, you do this hoping to stay warm by adding insulation They make it harder for heat to escape and hold the warm air around your body in place Insulators contain many air spaces that trap air, which a good insulator. Other example of insulators are plastic, wood, rubber, and ceramics (floor tiles)

Feeling the Heat On a hot summer day, would you rather sit on a seat made of fabric or vinyl that has been in the sun all day While both have been in the sun the same amount of time and the air around them is the same temperature, the vinyl seat feels hotter This is because the vinyl transfers heat faster than fabric The seat feels hotter because it transfers its energy to your skin much faster than the fabric seat

Convection Convection is the transfer of energy between objects or areas that differ in temperature This is most common in liquids and gasses As temperature increases, particles move around more quickly, this cause density to decrease Cooler denser materials cause warmer, less dense material upward See figure 19 on page 602 to see how your house can be heated through convection!

Examples of Convection Eagles and hawks seem to float along effortlessly high in the sky Sometimes birds can stay in the air without flapping its wings! In this case, the bird is held in the sky by a thermal – a column of warm air forced upward as the cool air around it sinks This is also known as a convection current This can also happen in water and is why oceans have water currents

Radiation Radiation is the transfer of energy through waves These waves can be visible light, or other types of waves you can’t see When these waves strike an object, it can transfer its energy to the object causing its temperature to rise This is how the Sun transfers its energy to the Earth A microwave cooks food by using microwave radiation to transfer energy to the food