Lesson 2 - Energy for Movement - Physics PDF

Lesson 2: Energy for Movement – 28/11/22 Starter: Struggling to Remember 1. a. Air resistance, 200 N 2. Upthrust, 5 N Thrust, 10 N 500 N...

Lesson 2: Energy for Movement – 28/11/22 Starter: Struggling to Remember 1. a. Air resistance, 200 N 2. Upthrust, 5 N Thrust, 10 N 500 N Weight, 700 N Drag, 2 N 1. c 8N Air resistance, 2100 N Weight, 5 N 1400 N 80 N Lift, 100 N Weight, 700 N 3. Thrust, 110 N Drag, 110 N 1. b. Air resistance, 700 N Weight, 20 N 0N Weight, 700 N Learning Objectives By the end of the lesson, you should know:  To appreciate that energy originates in the Sun.  To understand that energy is used by animals to carry out activities and that this energy comes from food, often in a food chain.  To know several forms of energy such as kinetic energy and internal energy.  To understand the difference between renewable and non-renewable energy sources and what energy stores are.  To know the conservation of energy. The Source of Energy?  The earliest forms of transport often used animals to carry things, or to pull sleds or carts with wheels. Animals, including humans, need energy in order to do jobs such as pulling a cart. We get this energy from food. The energy in our food can be traced back to the Sun.  Infact, the sun is the original source of most energy on Earth.  As we go through, list the stores and an example Energy Stores  We can get energy from many sources.  Peoplestarted to use coal around 200 years ago to power some forms of transport.  Coal is a non-renewable energy source, which means it will run out one day.  Coalis part of a family of non- renewables called fossil fuels which formed underground millions of years ago.  Other sources are renewable Chemical Energy Stores  Otherexamples of fossil fuels include oil and natural gas, which can be used in making electricity or in transport.  Fossil fuels have been convenient for storing large amounts of energy which can then be burned and turned into heat energy for home heating, cooking, and more. Kinetic Energy All moving things have kinetic energy; from atoms, to runners, to vehicles, to planets and stars. The amount of kinetic energy depends on mass and speed. The greater its mass and the faster its going, the more energy in its kinetic energy store. Gravitational Potential Energy Stores  We can also store smaller amounts of energy in springs and weights.  A clock (like the one on the right) uses weights to operate.  The weight on a chain will rise and fall and transfer energy to the clock.  Energy stored in raised objects is called gravitational potential energy. Elastic Potential Energy Stores The energy stored when an object is stretched or squashed. Some objects can change shape reversibly. Rubber balls, springs, elastic bands, catapults and balloons are like this. When a rubber ball is stretched or squashed, it can regain its shape again. Internal (Thermal) Energy Stores  Internal(or thermal) energy is the energy stored in an object in the movement of its particles.  There is more internal energy in hot objects and less internal energy in cold objects.  This energy can be transferred from hotter objects to cooler ones. Nuclear (atomic) energy stores  The energy stored in the nucleus of an atom. For example, uranium nuclear power, nuclear reactors.  Uranium is packs in a lot of energy. For example, one kilogram of uranium contains the around the same energy as 2,000,000 kilograms of coal. Electrostatic energy store  Some objects carry electrical charges and create electric fields. These charged objects can exert forces on each other.  You get an electric current when charged particles move through a wire. The energy stored when repelling charges have been moved closer together or when attracting charges have been pulled further apart. For example, thunderclouds, Van de Graaf generators. Magnetic energy store  Some objects can be magnetised and create magnetic fields, they can exert forces on other magnetised objects or magnetic materials.  Energy is stored when repelling poles have been pushed closer together or when attracting poles have been pulled apart. For example, fridge magnets, compasses, magnetic levitation (maglev) trains. Whiteboards  Origin of energy  Food Chains  Naming Stores Energy Pathways  Radiation – energy transmitted as a wave (e.g., electromagnetic waves, sound)  Heating – due to a temperature difference (e.g., conduction and convection)  Electrical – charges moving due to a potential difference (e.g., circuits)  Mechanical – A force moving an object through a distance Transferring Energy  Energy cannot be created or destroyed, only transferred between different forms. This is the law of conservation of energy.  Some energy transfers are not very useful to us.  Forexample, if you turn on a lightbulb some of the energy will be transferred as light (useful) but you will also transfer some energy as heat (not useful here). Transferring Energy  We can work out how good a device or process is at transferring useful energy by looking at efficiency.  Theefficiency of an energy transfer compares the useful energy transferred to the total energy transferred.  Notuseful (wasted) energy is usually transferred to the surroundings as heat, and often sound as well.  We say that the wasted energy is dissipated to the surroundings (spread out).  The greater the efficiency, the less energy is wasted. Energy Diagrams – Sankey These can be used to calculate efficiency Light Chemical energy store of (5J) fuel from Electrical power Pathway station (110J) Heat Energ y (105J) Whiteboards  Conservation of energy  Transfer Pathways  Transfers  Efficiency  Useful and wasted Teacher Demo  The items supplied (rubber band, mass holder and set of masses, pendulum, 1.5 V cell and bulb can be used to demonstrate various energy transfers. Tasks  Read the textbook pages 132-133, answer questions 1-9  15 minutes Complete worksheet – energy for movement  Complete worksheet - energy transfers and stores  Extension: End  Complete worksheet - Bungee jumping Extra Slides (advanced learning)  Energy Stores 1  Energy can be transferred usefully, stored or dissipated but is never created or destroyed. Instead it is just transferred between different energy stores and different objects. When energy is transferred to an object, the energy is stored in one of the objects energy stores. These stores are 1. Thermal energy store (internal) – The sum of the total kinetic and potential (molecular) energy of the particles in an object. This is the movement of the particles (translational, rotational and vibrational) – also know as thermal energy/ temperature/kinetic energy - and the energy of the bonds between particles – also known as chemical energy/molecular potential energy.  In most cases just the thermal/temperature/kinetic is can be considered roughly equivalent to internal. In hotter objects, the particles have more internal energy and vibrate faster. For example human bodies, hot coffee, stoves or hobs. Ice particles still have internal energy, but the particles vibrate slower. 2. Kinetic energy store – All moving things have kinetic energy; from atoms, to runners, to vehicles, to planets and stars. The amount of kinetic energy depends on mass and speed. The greater its mass and the faster its going, the more energy in its kinetic energy store. 3. Gravitational potential energy store – When an object is moved higher, it gains gravitational potential energy. The amount of gravitational potential energy it gains depends upon the mass, height and gravitational field strength. For example aeroplanes, kites, objects on a table. 4. Elastic potential energy store – The energy stored when an object is stretched or squashed. Some objects can change shape reversibly. Rubber balls, springs, elastic bands, catapults and balloons are like this. When a rubber ball is stretched or squashed, it can regain its shape again. Energy Stores 2 5. Chemical energy store – The energy stored in chemical bonds, such as those between molecules. For example, foods, muscles, electric cells. 6. Magnetic energy store – Some objects can be magnetised and create magnetic fields, they can exert forces on other magnetised objects or magnetic materials. Energy is stored when repelling poles have been pushed closer together or when attracting poles have been pulled apart. For example, fridge magnets, compasses, magnetic levitation (maglev) trains. 7. Electrostatic energy store – Some objects carry electrical charges and create electric fields. These charged objects can exert forces on each other. You get an electric current when charged particles move through a wire. The energy stored when repelling charges have been moved closer together or when attracting charges have been pulled further apart. For example, thunderclouds, Van de Graaf generators. 8. Nuclear energy store – The energy stored in the nucleus of an atom. For example uranium nuclear power, nuclear reactors.  Energy Transfers 1  A system is another word for a single object or a group of objects. When a system changes, energy is transferred. It can be transferred into or away from the system, between different objects in the system or between different types of energy stores. Closed systems are systems where neither matter nor energy can enter or leave – the net change in the total energy of a closed system is always zero.  Energy cannot be created or destroyed. It can be stored – and can remain in the same store for millions of years, or sometimes for a fraction of a second. Or energy can be transferred i.e. from a hot object to a cool object by conduction, convection or radiation. There are energy transfers going on all of the time – whenever a system changes, there is a change in the way some or all of the energy is stored. Some examples of energy transfers are shown in the images to the right.  Doing work is the scientific way of saying that energy has been transferred. For example, a grazing cow, a firing catapult and a boiling kettle are all doing work, as energy is transferred.  Energy Transfers 2 - Pathways  Energy can transfer or move from one store to another in different ways. Devices such as lamps and heaters may be involved, or processes such as combustion. For example, energy can be transferred:  When one object is hotter than another, energy is transferred by heating. Energy is transferred from the hotter object to the cooler one, and the difference in temperature between them decreases. An object does not contain heat, it contains internal energy. Heat is the transfer of energy. In short, this is due to a temperature difference often caused electrically or chemically.  Energy can be transferred mechanically through the movement of the parts in machines, and when the motion or position of an object changes. Sound waves and seismic waves (formed during earthquakes) are mechanical waves that transfer energy through materials and from place to place. In short, this is when a force moves an object through a distance.  Energy is transferred electrically when an electrical circuit is complete. A simple circuit may consist of a battery, lamp and wires. Internal energy stored in the battery is transferred to moving charged particles in the wire. In short, this is when a potential difference moves charges around a circuit.  Visible light, infrared light, microwaves and radio waves are forms of energy transfer by radiation. They are carried by waves (although unlike sound, these are not mechanical waves and can travel through empty space). Electric lamps and burning fuels transfer visible and infrared light to the surroundings. In short, energy transferred by waves.  Other transfers  When an object falls the gravitational potential energy is converted to kinetic energy. When it has fallen half of the way down, half of the energy will have been transferred and so on.  Food contains internal energy stored in the bonds between particles. This is sometimes called chemical energy. This is converted into the energy all living organisms need during respiration. This conversion is similar to burning, for example wood. Here internal energy in the wood is converted into heat and light given out by the flames.  Examples of energy changes  Here is a list of the example scenarios provided in Physics for You that the author suggests the energy transfers are identified (store to store, not pathways). The first one ‘torch’ was provided, the rest are your own – these may need updating if better understanding proves them to be wrong. The ones in red are your own examples. Torch – Chemical  Thermal (internal) An arm muscle lifting a weight – A falling parachutist – Gravitational Chemical  Gravitational Kinetic A car starting to drive off – Chemical  A wood fire – Chemical  Thermal (internal) Kinetic Hanging a weight on a spring – A battery connected to a resistor  Gravitational  Elastic Chemical  Thermal (internal) An atomic bomb – Nuclear  Chemical + A bow being stretched – Chemical  Kinetic + Thermal Elastic A bullet hitting a wall – Kinetic  Thermal An arrow released from a bow – Elastic  Kinetic Plants – Nuclear  Chemical Rubbing hands to keep warm – Kinetic  Lightning – Electrostatic  Thermal Thermal (internal) (internal) Rubbing a balloon to charge it up – Friction – Kinetic  Thermal (internal) Kinetic  Electrostatic A weight dropped on a desk – A solenoid – Electrostatic  Magnetic Gravitational  Kinetic A football rising into the air – Kinetic  Gravitational The sun shining on a solar water heater – Nuclear  Thermal (internal)