Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
WHAT IS ENERGY AND HOW DO FORCES TRANSFER ENERGY? ENERGY, what do you think of when you hear the word energy? Do you picture a speeding racecar or perhaps a spinning windmill? Maybe you imagine a street luge participant speeding down a twisting mountain road or you think of an explosion. We frequently read about energy in the newspaper. In the news, ENERGY usually refers to electrical energy or the energy stored in oil/gasoline. These are two good examples of energy that dramatically affect our daily lives. Are there other examples? How do we make use of this energy? Why are these two forms so important to us? Energy is a topic that makes its way into all of the sciences. As you move through this year’s science class you will learn about energy in many different forms and in many different contexts. Energy is hard to define, so we generally define it by providing examples of energy. Energy can move from one place to another and it can also change forms. Keeping track of the energy in an example can help you understand and explain the science involved. Why is energy so important to us? What types of energy do you encounter most often? How does energy get from one place to another? 1 © 2009 Delaware Science Coalition / Delaware Department of Education Section I: Reviewing Key Energy Concepts MAKING SENSE OF ENERGY … Energy is the most central concept in all of science. Energy is the thread that ties the physical, life, and earth sciences together. Matter and energy make up the universe. While matter is tangible and something that we can hold in our hands, energy is far more abstract. We commonly say that objects have energy, but we can’t really see this energy. We recognize energy mainly through the effects it has on objects. We see the changes that occur when an object or substance has energy and shares that energy with other objects. Energy is not easily defined. So scientists study energy by looking at the effects energy has on other things. A definition that is often used for energy is “the ability to bring about some sort of change.” If something has energy, then that energy can cause a change in the object or in its surroundings. By designing experiments to study these changes, scientists learn more about energy. Energy comes in many forms. You may remember some of these forms from your 8th grade study of energy or from previous studies in energy. It is important for us to be able to identify the forms of energy. It is also important to be able to describe how energy moves from one place to another and changes forms. In some cases, the same type of energy is simply passed along from one object to another; this is called an energy transfer. In other cases, the energy changes forms (converted from one form of energy to another form of energy); this process is called energy transformation. It is common for many energy transfers and transformations to happen together. It is often helpful, in order to understand a sequence of events, to create a description of how the energy 2 © 2009 Delaware Science Coalition / Delaware Department of Education moved. This is generally done using words and pictures; the result is called an energy chain. A REVIEW OF SOME COMMON FORMS OF ENERGY …. Mechanical Energy (ME) – the combination of potential and kinetic energies. Mechanical energy is a broad category of energy that includes the two main forms of energy, potential and kinetic. In many cases the combination of the two forms is an important quantity to keep track of, so the term mechanical energy refers to the sum of these two forms. Kinetic Energy (KE) – the energy of motion. The energy associated with moving objects is called kinetic energy (KE), and is often referred to as the most fundamental form of energy. The size of the KE is determined by an object’s speed and its mass. A moving baseball has kinetic energy. If you have ever been hit by a pitched ball, you are aware of the energy a moving object can have. Gravitational Potential Energy (GPE) – the energy of position. This is energy that an object possesses due to its position. The size of the GPE is determined by the object’s mass and its height above the ground. As a person climbs a ladder, increasing his/her height above the ground, he/she increases his/her GPE. Heat Energy (HE) – the random kinetic energy of particles. Heat energy 3 © 2009 Delaware Science Coalition / Delaware Department of Education is the random, and very disorganized, kinetic energy of the particles in a substance. Thermal energy is another term often used as a synonym for heat energy. In most cases the distinction between the exact definitions of heat energy and thermal energy is not made. Due to the random nature of this form of energy, it is difficult to make heat energy a useful form of energy. For this reason it is usually the form of energy that appears at the end of energy chains. It happens so often that scientists refer to heat energy as the “graveyard of energy”. For example, if you pound a nail into a piece of wood, the nail gets hot due to the energy transferred to it by the hammer and the force of friction with the wood. Chemical Potential Energy (CPE) – the energy of bonds. Chemical potential energy, sometimes just called chemical energy, is the energy stored in the bonds that hold the particles in a substance together. When these bonds are formed, or are broken, energy transfers and/or transformations take place. In many cases, the energy stored in the bonds of substances is transformed into other forms of energy. Food is a source of chemical energy for our bodies, so we sometimes use ‘food energy’ in place of chemical energy in energy chains that involve people. In most cases this chemical potential energy is later transformed into heat energy 4 © 2009 Delaware Science Coalition / Delaware Department of Education Electromagnetic Energy – the energy of waves. This form of energy is often referred to as solar energy or light energy. Electromagnetic energy is the energy that is carried by electromagnetic waves. The most common form of electromagnetic energy is “light”. Light energy is a term that can be used to describe the energy ranges that our human eyes are sensitive to and it may include some forms of ‘light’ that we can not see with our eyes, such as infrared and ultraviolet. The sun is the most important source of electromagnetic energy for the Earth, supplying the vast majority of our planet’s energy. In some cases, chemical potential energy can be transformed into electromagnetic energy. This form of energy is very important in the scientific field of astronomy. Electrical energy is a subset of electromagnetic energy, characterized by moving charges. It is used to run appliances and make artificial light. When the charged particles vibrate, they transfer energy by electromagnetic waves. 5 © 2009 Delaware Science Coalition / Delaware Department of Education Sound Energy – the energy of vibrating particles. This form of energy is transferred by mechanical waves. The particles that make up a substance vibrate in a highly organized manner and transfer energy through the substance. The particles in the substance vibrate, but do not change their location. In most cases, sound energy is classified into three categories; infrasonic is the sound that is below our human hearing level, sonic is the sound that our human ears are sensitive to, and ultrasonic is the sound that is above our human hearing level. Have you ever made a tin can telephone? If so, you have already experimented with sound waves and how vibrations are involved in the energy transfer process. A good example of the use of sound waves is sonar. Humans have created devices that enable us to send out a sound wave and listen for the echo so that we can determine how far away something is to the source. Seismic waves or “earthquake” waves also fit into this category because they involve the transfer of energy through vibrating matter in the form of mechanical waves. Ultrasounds in the medical field are used for a variety of purposes. Perhaps you have seen an ultrasound image of a baby. In most energy chains, the sound energy is transformed into heat energy (the disorganized and random KE of particles Elastic Potential Energy (EPE) – energy of deformed materials. 6 © 2009 Delaware Science Coalition / Delaware Department of Education This form of energy comes from the stretching or compressing of elastic materials. When an elastic material is deformed (by stretching or compressing), it exerts a force, called the elastic force, to return to its original shape. In many cases, the elastic material is held temporarily in this deformed position and the material has a stored amount of energy. Bow hunters make use of EPE to shoot their arrows. The EPE of the bow string is converted to the KE of the arrow. Catapults and slingshots also operate in this manner. Tennis players rely on the elastic properties of their tennis racquets and the tennis ball. Pole vaulters depend on the stored energy in the bent pole to help them get over the bar. The science behind the design of the pole relies on knowledge of how material store EPE. Surprisingly, certain types of rock can have elastic properties. They can be stretched or compressed under huge forces. TWO IMPORTANT PROPERTIES OF ENERGY ARE: Energy transfer is the passing of energy from one object to another. 7 © 2009 Delaware Science Coalition / Delaware Department of Education Energy transformation is the changing of energy from one form of energy to another form of energy. MAKING SENSE OF ENERGY … the Law of Conservation of Energy 8 © 2009 Delaware Science Coalition / Delaware Department of Education GOALS Review the concepts of energy transfer and energy transformation and the basic forms of energy Discuss the significance of the Law of Conservation of Energy. Describe how force and distance combine mathematically to quantify the energy transfer in a process called work. Quantify the work done (energy transferred or transformed) in examples. Create and explain energy chains. CONNECTIONS Scientific Content – Energy can exist in different forms. Energy can be categorized into several forms (kinetic, potential, elastic, heat, electrical, etc.) Since energy can not be seen, it is defined by the change that is produced when energy is transferred and/or transformed. Mechanical energy is the sum of both the kinetic energy (KE) and the Gravitational Potential Energy (GPE) of an object. KE is dependent upon the mass and speed of the object; GPE is dependent upon the mass and the height of the object. Chemical potential energy (or chemical energy) is the potential energy stored in the bonding of the particles that make up matter. Heat energy is the random kinetic energy of the particles that make up a substance. Electromagnetic energy is the energy transferred by electromagnetic waves Elastic potential energy is the energy stored in elastic materials by compressing or stretching them beyond their normal position. Sound energy is the energy carried by the organized vibrations of particles as a mechanical wave. Energy can be transferred from one object to another. An energy transfer occurs when energy is passed from one object to another object but stays in the same form. When one object pushes or pulls on another object often (but not always) energy is transferred from one of the objects to the other. As a result of this transfer, the motion of one or both of the objects will change. When a force transfers energy, the process is called work. The “work done” by the force involved in the energy transfer can be 9 © 2009 Delaware Science Coalition / Delaware Department of Education quantified by multiplying the force by the distance over which that force acted during the energy transfer process. When kinetic energy is transferred to a large stationary solid this energy is transferred to the particles that make up the object. The kinetic energy may take the form of organized vibrations within the solid (a mechanical wave), but will ultimately become the random vibrational kinetic energy of the particles. This collective random kinetic energy of the particles is called heat energy. Energy can be changed from one form to another. This process is called the transformation of energy. An energy transformation occurs when energy is passed from one object to another and it changes forms. In most cases, the energy of objects eventually becomes the random kinetic energy of the particles that make up the object. We call this form of energy heat energy. By understanding energy transformation and energy transfer, we can begin to understand that the energy of an object can change forms and be passed to other objects but cannot be created nor destroyed. Energy can not be created nor destroyed. Energy can be transferred from one object to another and can be transformed from one form to another, but the total amount of energy never changes. This concept is known as the Law of Conservation of Energy and is one of the most significant laws in science. Identifying the energy transformations and transfers that occur when an event takes place helps us to better understand what factors influence these changes. This understanding helps us to appreciate how objects interact and enable us to make predictions about the outcomes of these changes. Energy chains help to understand the Law of Conservation of Energy. Identifying where energy comes from and where it goes builds an acceptance that energy can change form, or be transferred from object to object, but cannot disappear. When energy seems to go away, it really is just changing forms and spreading out. These concepts are the foundation for the Law of Conservation of Energy. Scientific Process Identifying the different forms of energy, and where it is transferred and/or transformed during an event are important skills that lead to a richer understanding of the flow of energy in everyday phenomena. 10 © 2009 Delaware Science Coalition / Delaware Department of Education Creating energy chains requires an understanding of the flow of energy that takes place during the changes in any physical system. Accurate completion of an energy chain and/or diagram reflects a student’s understanding of the flow of energy in systems. Math/Graphing Calculations of work will be completed. Graphical displays of energy flow will be created and analyzed. 11 © 2009 Delaware Science Coalition / Delaware Department of Education