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Unit 6: Energy. In this unit, you will explore what energy is and what it does. Lesson 1: Energy. In this lesson, you will learn how scientists define energy. You will explore different forms of energy and how they are a part of our everyday lives. What Is Energy?.
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Unit 6: Energy In this unit, you will explore what energy is and what it does.
Lesson 1: Energy In this lesson, you will learn how scientists define energy. You will explore different forms of energy and how they are a part of our everyday lives.
What Is Energy? • Energyis the ability or capacity to do work. • Work is using an applied force to make an object move. • Making changes in the physical world • Withenergy, changes in the physical world are possible. • These can be a change in speed, a change in direction, a change from cold to hot, and many other kinds of changes.
Forms of Energy We encounter many different kinds of energy every day. Some of the forms of energy are: • mechanical • chemical • electrical • sound • light • nuclear
Mechanical & Chemical Energy • Mechanical energy-the energy of motion and position. • It is the combination of two forms of energy–potential energy-stored energy that is associated with the position of an object andkinetic energy-the energy of an object or substance because of its motion. • Chemical energy-form of potential energy stored in chemical bond. • For example, we can use natural gas to heat homes and fuel cooking stoves.
Electrical & Nuclear Energy Electrical energy is associated with electric charges. • It can be sent along wires because of the way that electrons move within the wire, exert forces, and transfer energy. • Electrical energy is used to light our homes and schools and power our appliances. Nuclear energy is energy that can be released by changes in the nucleus of an atom. • Nuclear energy is obtained when atoms of elements like uranium and plutonium are split during a process called nuclear fission-the splitting of the atoms releases large amounts of nuclear energy. • A nuclear power plant uses this nuclear energy to generate electrical energy
Sound &Light Energy Sound Energy-the energy produced when matter vibrates • When you speak, your vocal cords vibrate. You can feel the vibrations when you touch your neck. Light energy is a form of electromagnetic energy, the vibration of electrically charged particles. • It is the vibration of electrically charged particles that send the light energy out into the space around them.
Conservation of Energy This law states that energy can neither be created nor destroyed, but it can be transformed. • This means that energy can be transferred from place to place and can also be converted between the different forms of energy. • But whether transformed or converted, the amount of energy is always conserved; it cannot be created or destroyed.
Energy Transformations Some examples of energy transformations: • Gasoline contains chemical energy. When it is burned, it is transformed into heat energy and into mechanical energy, which is needed to make vehicles move. Although the form of energy changes, no energy is lost or gained. • Electrical energy is used to power radio speakers. The speakers work by transforming electrical energy into sound energy. Sound energy causes your ear drums to vibrate and enables you to hear the music. Energy is not gained or lost, but it changes form.
Sources of Energy Energy resources can be categorized as either renewable or nonrenewable. • A renewable energy resource is one that can be replaced. Ex. Sunlight, wind, moving water, and wood • A nonrenewable energy resource is one that cannot be replaced. Ex. Oil, natural gas, coal, and uranium.
Measuring Energy Energy can be measured using the SI unit called the joule (J). • One joule of energy is used when a force of one newton is applied over a distance of one meter. • While the newton-meter is the unit of work, physicists found this term cumbersome, so they decided to call one newton-meter a joule. • 1 joule (J) = 1 newton-meter (N •m)
Lesson 2: Work In this lesson, you will explore the scientific meaning of work.
Work • In scientific terms, a force exerted on an object does work when the object moves a distance in the direction of the force. • So, you do work by using an applied force to move an object. • When the force does work on the object, the object moves in the same direction as the force.
Work Depends on Force and Distance • Even a great amount of force applied to an object may not always do work. • You may feel tired from trying to move an object, but since it did not move, no work was done on it. • Work involves both force and motion in the same direction. • It can be expressed by the following equation: • W = Fdwork = force x distance
Power • In scientific terms, power is the rate at which work is done. • Powermeasures how fast work happens, or how quickly energy is used. • Time does become a factor when calculating power. • It can be calculated using the following equation: • P = W/tpower = work/time
The Watt • Poweris measured in the SI unit of watts (W). • One watt is equivalent to one J/s. ***Note that the symbol for watt (W) is similar to the symbol for work (W). Both symbols use an uppercase W, but the symbol for work is italicized. Make sure you don’t confuse the two when interpreting formulas or completing calculations
Lesson 3: Kinetic Energy In this lesson, you will explore kinetic energy and learn how kinetic energy relates to moving objects, how it can change, and how it can be calculated.
Energy in Motion • Kinetic energy is the energy an object has while it is inmotion. • Allmoving objects have kinetic energy. • Kinetic energy enables moving objects to perform work on other objects. • Objects only have kinetic energy while they are in motion. When an object stops moving, its kinetic energy is zero.
Kinetic Energy Depends on Mass & Speed Mass: • The amount of kinetic energy (KE) of a moving object depends on its mass. • A baseball has a greater mass than aping-pong ball, so greater kinetic energy. Speed: • Kinetic energy of a moving object also depends on how fast it is going. • The object that has greater speed will have greater kinetic energy if they are both the same mass. ***Refer to K12 lesson for examples of both.
Kinetic Energy Equation The kinetic energy of a moving object depends on both its mass and speed. This relationship is represented by the following equation: • KE = ½mv2kinetic energy = ½ (mass) (speed)2 • In this equation, mis used to represent mass (kg). The symbolv is used to represent speed (m/s). Therefore, v represents speed. Step to solve for kinetic energy (Recall order of operations): • square the quantity for speed • multiply one half the mass • multiply these two numbers together • write the resulting answer in joules (J) *** This may seem confusing at first, but remember that velocity without direction is simply speed. In the equation for kinetic energy, direction is not a factor.
Some Kinetic Energy Examples • Changes in Kinetic Energy • Kinetic Energy of a Pendulum • Kinetic Energy of a Swing
Lesson 4: Potential Energy In this lesson, you will explore a form of energy called potential energy. You will learn when objects have potential energy, and how potential energy can become kinetic energy.
Energy of Position • Potential Energy(PE)-the stored energy an object has due to its position or shape. • Objects that have potential energy are not moving. • Potential energy can either be elastic or gravitational.
Elastic Potential Energy • When a flexible object, such as a bow or a spring, is bent, stretched, or compressed from its natural shape, it stores elastic potential energy. • Elastic objects tend to return to their natural shape unless a force is acting on them. • So when the shape of an elastic object is changed, it stores elastic potential energy (EPE) before it returns to its natural shape
Gravitational Potential Energy • Objects can also store potential energy due to their position. • Objects take on gravitational potential energy when they are lifted against the force of gravity to a position where they have the potential to fall. • Gravitational potential energy (GPE) is a property of elevated objects.
Gravitational Potential Energy Equation • The amount of GPE an object has depends on the object’s weight (N) and height (m). • The height of an object is measured in relation to a reference point, such as the height above the floor. • The formula for calculating gravitational potential energy is PE = w x h, where potential energy = (weight) x (height).
Converting Potential Energy to Kinetic Energy & Changes in Potential and Kinetic Energy • Objects at rest can have potential energy due to their shape or position. • A change in their shape or position can set them in motion. • Objects in motion have kinetic energy. Therefore, potential energy can be converted into kinetic energy. • For many systems, we can predict how potential energy and kinetic energy will increase and decrease. • K12 Ex. Roller Coaster
Lesson 7: Using a Lever This lesson investigates a lever and will introduce you to this section that examines work, energy, and machines.
Lever A leveris a machine consisting of a beam or rigid rod pivoted at a fixed hinge, or fulcrum.
Lesson 8: Simple Machines In this lesson, you will learn what defines a machine in physics. You will explore different types of simple machines and how they are used to do work.
What Is a Machine? • Work is applying a force to move an object over a distance. • A machine is any device that makes work easier…by changing the strength or direction of a force. • Machines do not decrease the amount of work that needs to be done, they just make work easier by changing the way it is done. • Machines don’t just have buttons, knobs, and moving parts…many everyday objects, such as rakes, bottle openers, and ramps, are machines.
Machines Make Work Easier • Simple Machine is a machine that makes work easier when a single force is applied. • Simple machines cannot do work by themselves…energy be must provided to make a simple machine do work.
Input and Output Forces When you use a simple machine, you apply a force…called the input force. The force that the simple machine applies to an object is called the output force. The machine magnifies the input force, so that the resulting output force is greater. The work you apply to a simple machine is always equal to the work the simple machine applies on an object. • 6types of simple machines: • lever • inclined plane • screw • wedge • wheel and axle • pulley
Levers • A lever is a simple machine that consists of a rigid bar that pivots on a fixed point called a fulcrum. • Levers can change the direction of a force. • Levers can also change the strength of a force • K12 Ex. Seesaw, bottle cap, shovel, crowbar, and a rake.
Inclined Plane • An inclined plane is a flat, slanted surface, often used to lift things…changing the strength of a force. • The longer an inclined plane, the less force is required to move an object upward. • With a longer ramp, the distance to the bus would be longer because the ramp would extend out further into the road.
Screw • A screw is another type of simple machine. • It is an inclined plane wrapped around a post. • The inclined plane makes up the threads of the screw. • Imagine that you could unwind the threads of a screw. • The closer together the threads are, the longer the inclined plane, and the smaller input is force required to get the same output force.
Wedge • A wedge is a two-sided inclined plane that can be used to separate materials. • A wedge changes the direction of a force. • As with all inclined planes, wedges that are long require less input force for the same output force than wedges that are short. • K12 EX. Ax, some knives, chisels, and teeth
Wheel and Axle • A wheel and axle is a simple machine composed of two attached circular objects that rotate in the same direction. The larger object (the outside) is the wheel, and the smaller object (the inside) is the axle. • This type of simple machines, the input force acts on the axle, and the output force is exerted by the wheel.
Pulley • A pulley is a simple machine consisting of a grooved wheel that holds a rope or a cable. • Pulleys are often used to help lift objects. • A pulley can also change the strength of a force. • Pulleys that move with a load reduce the force needed to lift the load as it is moved over a longer distance.
Simple Machines Revisited: • A lever is a simple machine that consists of a rigid bar that pivots on a fixed point called a fulcrum. Levers change direction and strength of force. • An inclined plane is a flat, slanted surface, often used to lift things. Changes the strength of force.
3. A screw is another type of simple machine. It is an inclined plane wrapped around a post. 4. A wedge is a two-sided inclined plane that can be used to separate materials
5. A wheel and axle is a simple machine composed of two attached circular objects that rotate in the same direction. 6. A pulley is a simple machine consisting of a grooved wheel that holds a rope or a cable as shown in the first photo.
Lesson 9: Compound Machines In this lesson, you will explore how simple machines work together in compound machines.
Simple vs. Compound Machines Machines make work easier by changing the strength or direction of a force. • Asimple machine is a machine that makes work easier when a single force is applied. • Compound machines are made up of two or more simple machines. • Like all machines, they make work easier by changing the strength or direction of a force. • A compound machine may involve more than one movement, and more than one force may act on a compound machine. • K12 Ex. The metal clasp of a zipper is made up of three wedges
Combining Different Simple Machines Compound machinescan also be a combination of different types of simple machines. A can opener combines threedifferent types of simple machines. It is made up of a wedge, a wheel and axle, and two levers. • Wedge: The blade is a wedge that cuts through the metal as the can opener moves. • Wheel and Axle: To move the can opener, you turn a wheel. The wheel turns an axle. The axle turns gears that keep the can opener gripped to the can and help it move. The gears also turn the wedge that cuts the can. • Levers: The arms of a can opener’s handle act as levers. When you squeeze them over the lid of a can, a blade attaches to the lid’s edge
Bike Parts are Simple Machines A bicycle also combines several different types of simple machines to do work. • Wheels and Axles: The wheels of a bicycle are wheels and axles. • Levers: The pedals are part of a lever. The gearshifts and brake controls on the handlebars are levers, too. • Pulley: The lever with the pedals turns a pulley that holds the bicycle’s cha
Work, Force, and Distance in Compound Machines • Recall that work is represented by the equation W = Fd. In other words, to complete the same amount of work, you can decrease the amount of force you need to use by spreading it over a longer distance. Or, you can decrease the amount of distance you need to cover by increasing the amount of force you use. Let’s look at how this relationship applies to compound machines. • Suppose you use a pair of scissors, like the top photo, with long blades and a short handle to cut an object. The force of the blades coming together is spread along the blades’ length. Therefore, you can make a long cut, but the force of the cut is weak. This tool is good for cutting paper and fabric. • Now suppose you use a pair of scissors, like the bottom photo, with a short blade and a long handle to cut an object. The force of the blades coming together is spread over a short distance. Therefore, the cut is short, but the force is strong. This type of scissor is good for cutting sheet metal and heavy materials
Lesson 11: Thermal Energy In this lesson, you will explore a form of energy called thermal energy.
