What is Energy? What is the relationship between energy and work? Compare kinetic and potential energy What are the different types of energy? What is energy? Energy is the ability to do work. Great, but what is work? Work is done when a force (caused by energy) causes an object to move. Work = Force x distance Energy / Work Energy is needed to push a box across the floor. The box moving across the floor is an example of work. Energy is needed to hit a home run. The ball flying over the fence is an example of work. Two Basic Types of Energy Potential Energy = the energy of an object due to its position, shape, or condition Kinetic Energy = the energy of an object due to the object’s motion Potential Energy Not all energy has to do with motion. Potential Energy is the energy an object has because of its position, shape, or condition. Objects with potential energy have the potential, or ability, to do work. Potential Energy Preview We will learn about three kinds of Potential Energy 1. Elastic Potential Energy Potential Energy 3. Gravitational Potential Energy 2. Chemical 1 Elastic Potential Energy The bow has energy because work has been done to change its shape. The energy of that work is turned into potential energy. When the arrow is released the potential energy of the bow and string will be transferred to the arrow, sending it flying through the air. Elastic Potential Energy Compressed, or squished, springs also have potential energy. A spring has energy because work has been done to change its shape. Just like the bow, the energy of that work is turned into potential energy. Elastic Potential Energy What about rubber bands and other things that stretch? Elastic Potential Energy How do we “release” the potential energy stored in springs? Chemical Energy Chemical Energy is the potential energy stored in substances. Calories = the chemical energy of food Batteries also have chemical energy It all depends upon the position and arrangement of the atoms in a compound. Chemical Potential Energy A battery has potential energy due to its condition. Potential Energy is stored in the chemicals within the battery. A fully charged battery has the potential to do work. Chemical Potential Energy Chemical Potential Energy can be found in food. Calories! Chemical Energy (cont’d) Which type of food has the highest chemical potential energy (calories)? Gravitational Potential Energy When someone pushes you on a swing, you and the swing gain potential energy because work has been done to change your position. 2 You will have the most potential energy at the top, right before you begin your arc downward. Think about swinging. When will you have the most kinetic energy? Gravitational Potential Energy When you lift an object, you do work on it. You use a force that is against the force of gravity. When you do this you transfer energy to the object and give the object Gravitational Potential Energy. The amount of Gravitational Potential Energy an object has depends on the objects weight and height above the ground. Gravitational Potential Energy Books on a shelf have Gravitational Potential Energy. Which books have the most Gravitational Potential Energy? Why? Gravitational Potential Energy A man and his cell phone are on a ledge outside a very tall building. Which object (the man or his cell phone) has the most Gravitational Potential Energy? Why? How do we calculate Gravitational Potential Energy? GPE = Weight x Height Measure Weight in Newtons (N) Measure Height in meters (m) The unit for Gravitational Potential Energy = Newton meters (Nm) or Joules (J) Calculate the Gravitational Potential Energy GPE = Weight x Height Book #1 weighs 25 N on a shelf that is 2 meters off of the ground. Book #2 weighs 25 N and is on a shelf only 1 meter off of the ground. Which book has the most GPE? Calculate the Gravitational Potential Energy GPE = Weight x Height Man weighs 300 N on a ledge that is 200 meters off of the ground. 3 Cell Phone weighs 15 N and is on the same ledge. Which object has the most GPE? Practice Calculating GPE GPE = Weight x Height Tools: Metric tape measure, spring scale (be sure to use the Newton scale), calculator Units! Units! Units! ~ The units for GPE are Newton meters (Nm) or Joules (J) Potential Energy Review We learned about three kinds of Potential Energy 1. Elastic Potential Energy 2. Chemical Potential Energy 3. Gravitational Potential Energy Kinetic Energy Preview Kinetic Energy is the energy of motion or energy in use Any matter in motion has Kinetic Energy There are many forms of Kinetic Energy Some forms include: light, thermal, sound, electrical, and mechanical Mechanical Kinetic Energy Kinetic Energy = the energy of an object due to the object’s motion All moving objects have kinetic energy Kinetic Energy depends on Mass and Speed Mechanical Kinetic Energy (cont’d) KE = mass x speed x speed divided by 2 The greater the mass of a moving object, the more Kinetic Energy it has. The faster something is moving, the more Kinetic Energy it has, also. Mechanical Kinetic Energy Which animal has the bigger mass? 4 Which animal is able to move faster? Which animal has the greatest KE? KE = mass x speed2 2 Calculate the Mechanical Kinetic Energy (KE) KE = mass x speed2 2 Mass = 0.2 kg Speed = 2 meters/sec KE = 0.4 J Mechanical Kinetic Energy KE = mass x speed2 2 Mass = 4000 kg Speed = 2 meters/sec (Note that the elephant is going the same speed as the mouse.) KE = 8000 J What effect does an increase of speed have on Mechanical Kinetic Energy? The green and yellow cars have the same mass (1,200 kg) The green car is traveling at a speed of 20 m/sec The yellow car is traveling at a speed of 30 m/sec Calculate their Kinetic Energies KE = mass x speed2 2 Which car has the most KE? Green car’s KE = 240,000 J Yellow car’s KE = 540,000 J Speed has a greater effect on KE than mass because in the equation speed is squared. In other words, the faster an object is going . . . the more KE is has. Practice Calculating KE Use Joules (J) as the unit for Kinetic Energy 5 Tools: meter tape, stop watch, scale, calculator KE = mass x speed2 2 How are Kinetic and Potential Energy Related? Law of Conservation of Energy Energy can not be created or destroyed It can be transformed, or changed, from one form to another Kinetic Energy can be transformed into Potential Energy or other types of Kinetic Energy, and vise versa. This can and does happen many times. The total amount of energy doesn’t change. A book on a shelf ledge has potential energy. It has stored the energy that it took to lift it to the shelf. If the book is bumped and it falls, the potential energy changes to the kinetic energy of motion. When does the book have the most potential energy? When does the book have the most kinetic energy? Other Forms of Kinetic Energy Mechanical Thermal Energy or Heat Energy Electric Energy Sound or Acoustic Energy Light Energy 6 Radiant Energy Nuclear Energy Dynamic Mechanical Energy Imagine a juggler Sometime the objects have a lot of kinetic energy Sometimes the objects have a lot of potential energy Thermal Energy All matter is made up of atoms Atoms are in constant motion Thermal energy (heat) is all of the kinetic energy due to the random motion of atoms Thermal energy also depends upon the amount of atoms that are moving Solids The atoms in an ice cube vibrate in fixed positions and do not have a lot of kinetic energy. Liquids Atoms of water in a lake can move more freely and have more kinetic energy than atoms in ice do. Gas The atoms of water in steam move rapidly, so they have more energy than the particles in liquid water or ice do. Thermal Energy (cont’d) Thermal energy depends upon the amount of atoms that are moving. Consider, a cup of tea and the water in a bath tub. Both are the same temperature. Which has more thermal energy? ? ? ? ? ? ? ? The water in the bathtub has more thermal energy. Why? Simply because it has more water molecules. 7 Conduction Conduction is the transfer of energy through matter from particle to particle. It is the transfer and distribution of heat energy from atom to atom within a substance. Conduction is most effective in solids-but it can happen in fluids. Conduction (cont’d) For example, a spoon in a cup of hot soup becomes warmer because the heat from the soup is conducted along the spoon. Conduction (cont’d) Have you ever noticed that metals tend to feel cold? Believe it or not, they are not colder! They only feel colder because they conduct heat away from your hand. You perceive the heat that is leaving your hand as cold. Conduction (cont’d) Some items are conductors, they conduct heat well. Example: metal Some items are insulators, they DO NOT conduct heat well. Examples: fabric, wood, wool, and some plastic Think about it . . . What do we use a “cooler” for? What do we use a coffee mug for? Differences / Similarities? Convection Convection is the transfer of heat by the actual movement of the warmed matter. Heat leaves the coffee cup as the currents of steam and air rise. Convection is the transfer of heat energy in a gas or liquid by movement of currents. Convection (cont’d) Convection is responsible for making macaroni rise and fall in a pot of heated water. The warmer portions of the water are less dense and therefore, they rise. Meanwhile, the cooler portions of the water fall because they are denser. 8 Electrical Energy Electrical Energy is the energy of moving electrons. Electricity is the flow of electrical power or charge. Electrical Energy (cont’d) It is a secondary energy source which means that we get it from the conversion of other sources of energy, like coal, natural gas, oil, nuclear power and other natural sources, which are called primary sources. Electrical Energy (cont’d) The energy sources we use to make electricity can be renewable or nonrenewable, but electricity itself is neither renewable or non-renewable. Two types of electricity: Static and Current Static electricity is usually caused when certain materials are rubbed against each other, like wool on plastic or the soles of your shoes on the carpet. It is the attraction of two objects because one has a positive charge and the other has a negative charge. Two types of electricity: Static and Current The flow of electrons is called an electric current Look familiar? Some items are conductors, they conduct electricity well. Example: metal Some items are insulators, they DO NOT conduct electricity well. Examples: fabric, wool, wool, and some plastic Semiconductors Some items are semiconductors. The ability of a semiconductor to conduct electrictiy is between the ability of a conductor and an insulator. Resistors Resistors resist the flow of electrons. They are really good at transforming electrical energy into other forms of kinetic energy (sound, light, heat). We find resistors in radios, light bulbs, and ovens. 9 Sound or Acoustic Energy Sound Energy is caused by an object’s vibration. Sound is a type of energy made by vibrations. When any object vibrates, it causes movement in the air particles. These particles bump into the particles close to them, which makes them vibrate too causing them to bump into more air particles. This movement, called sound waves, keeps going until they run out of energy. If your ear is within range of the vibrations, you hear the sound. Sound Energy (cont’d) Picture a stone thrown into a still body of water. The rings of waves expand indefinitely. The same is true with sound. Sound Energy (cont’d) Irregular repeating sound waves create noise While regular repeating waves produce musical notes Sound Energy (cont’d) When the vibrations are fast, you hear a high note. When the vibrations are slow, it creates a low note. Playing the Guitar Stretching a guitar string, stores potential energy in the string Letting it go causes the potential energy to be transformed into kinetic energy This makes the string vibrate Playing the Guitar (cont’d) The vibrating string transfers some of this energy to the surrounding air The vibrating air travels to your ear When this energy reaches your ear, you hear the guitar Radiation Electromagnetic waves that directly transport ENERGY through space. Sunlight is a form of radiation that is radiated through space to our planet. The sun transfers heat through 93 million miles of space. The energy travels through nothingness! No matter required! 10 Radiant Energy Radiant energy is energy in the form of electromagnetic waves. Radiant energy can travel through a vacuum. Examples of radiant energy = visible light, infrared light, microwaves, radio waves, ultra violet light, X-rays, and gamma rays. Light Energy Light energy is produced by the vibrations of electrically charged particles. Unlike sound energy, the vibrations that transmit light energy do not need to be carried through matter. Light Energy (cont’d) In fact, light energy can move through a vacuum (an area with no matter). Also known as visible light energy. Nuclear Energy Nuclear Energy is the energy that comes from changes in the nucleus of an atom. A lot of potential energy is stored in the nucleus of atoms When two nuclei join together, or when a nucleus splits apart, a lot of energy is released. This is nuclear energy. Nuclear Energy (cont’d) Fusion = The joining of two nuclei. This happens on the sun. Fission = The splitting of a nuclei. Fission is used in nuclear power plants to generate electrical energy. Review Energy is the ability to do work Work is the transfer of energy Energy and Work are expressed in units of joules (J) Review (cont’d) Kinetic Energy is energy of motion It depends on speed and mass Review (cont’d) Potential Energy is energy of position, shape, or condition 11 Gravitational Potential Energy depends on weight and height Review (cont’d) Energy exists in many forms Each form has its own characteristics Some of the forms we looked at were: mechanical, thermal, chemical, electrical, sound or acoustic, light, radiant, and nuclear energy 12