Temperature
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
Chemical Reactions
Chemical Reactions and Energy Have you ever seen fireflies glowing at night, or perhaps a glow stick? Ever wonder what causes them to glow? Energy in the form of light is released when a chemical reaction takes place inside the glow stick Everyday, you take advantage of the energy released by many chemical reactions
What is a Chemical Reaction In a chemical reaction, compounds are broken down or new compounds are formed Some chemical reactions occur when atoms or molecules come together New compounds are formed when atoms and molecules come together and bonds are formed between them Compounds are broken down when the bonds between them are broken and those atoms become free to form new compounds
What is a Chemical Reaction When a fire burns, bonds between the atoms that make up the wood are broken These atoms then combine with atoms in the air to form new compounds As these new compounds are formed, light and heat are given off
Chemical Bonds Energy is stored in the bonds between the atoms in a compound The energy stored is potential energy in the form of chemical energy Chemical energy stored in the bonds of oil, gas, and coal are important sources of energy The chemical energy stored in food are important sources of energy for your body Your body transforms chemical energy into kinetic energy when your muscles move
Energy in Reactions In every chemical reaction, transformation in energy occur To break bonds, energy must be added, to create those bonds, energy must be released For example, when a lit match is placed in a mixture of hydrogen and oxygen gas, an explosion occurs Energy stored between the bonds of the hydrogen and oxygen gas is released Water is formed when bonds are reformed between the hydrogen and oxygen
Energy Absorbing Reactions Some chemical reactions need a constant supply of energy to keep them going Chemical reactions that absorb heat energy are called endothermic reactions Cooking food is an example on an endothermic reaction The food absorbs thermal energy as it cooks, when the food is removed from the heat, it stops the cooking process
Energy Absorbing Reactions Chemical reactions occur when sunlight strikes the leaves of plants These reactions convert the energy contained in the sunlight to chemical energy contained in a type of sugar Oxygen is also produced in this reaction called photosynthesis When a plant is deprived of sunlight, this process stops Photosynthesis is probably the most important chemical reaction on the planet since it provides all other living things with oxygen
Energy Releasing Reactions Endothermic reactions are usually important because of the compounds they release Other reactions are important because they release energy Exothermic reactions are reactions that release energy When a substance burns, it combines with oxygen atoms in the air and energy is given off in the form of heat and light
Energy Releasing Reactions An exothermic reaction that occurs when a material burns by combining with oxygen is called combustion Burning oil, coal, and gas produces much of the energy we need to heat homes and schools
Rate of Reaction Chemical reactions can occur at different rates They occur very fast in the case of fireworks, however if you leave metal outside for a long time, it will slowly begin to rust Rusting is chemical reaction between metal and oxygen and occurs much slower than a fireworks explosion An enormous amount of chemical reactions are occurring in your body every second The rate of these reactions are carefully controlled by your body
Changing the Rate of Reactions Two ways to change the rate of reactions are by changing the temperature and by adding a compound called a catalyst If you pour cake batter into a pan and leave it on the counter for several hours, nothing will happen However, if you put that pan in the oven, the batter will become cake Raising the temperature of the cake in the oven caused the substances in the batter to react more quickly
Energy Releasing Reactions A catalyst is a substance that changes the rate of a chemical reaction without any change to its own structure Many cell processes in your body are controlled by the presence of catalysts called enzymes Enzymes are found throughout your body and are important for growth, respiration, and digestion When you chew your food, an enzyme called saliva is released into your mouth
Energy Releasing Reactions Saliva helps break down starches in food into smaller molecules Many other chemical reactions also depend on catalysts The production of vegetable shortening, synthetic rubber, and high-octane gasoline are chemical processes that occur with the help of catalysts
Light Energy
Light Light is energy and travels in waves Light waves travels in straight lines Light travels VERY FAST, it can go around the world 8 times in 1 second!
Reflection When light hits a surface it can bounce off or be absorbed When the light bounces off a surface, this is called reflection The Law of Reflection states that light gets reflected at the same angle in which it hits a surface
Reflection Light will bounce off a shiny surface with a clear reflection Light will bounce off a dull surface with a diffuse reflection which will appear blurry
Refraction When light travels through different mediums (materials) it can speed up or slow down Light travels through air faster than water When light changes speed, light rays appear to bend Therefore a pen placed in water will look like this since the light rays slow down when they hit the water
Lenses When light passes through an object, the shape of that object can have an affect on the light wave Objects such as telescopes and binoculars use lenses - a curved piece of glass or plastic used to focus an image
Lenses For us to see an object that is far away, the light must travel through a lot of air This can cause the image to get blurry Lenses can refocus that image to let us see the image more clearly. Telescopes let us see images that are far away very clearly because they use lenses to refocus the light for our eyes
Concave Lenses Concave lenses are thinner in the middle and thicker on the outside They cause an image to be refocused and appear smaller A telescope uses concave lenses to make objects in the night sky appear clear and close up
Convex Lenses Convex lenses are thicker in the middle and thin out as you go to the edges These lenses cause images to appear larger They can also refocus an image that has become blurry People who wear glasses have a condition where images received by the eye are focused at the wrong point The lenses of their glasses refocus the image at the correct spot so they can see clearly