Work and Energy.pptx

WORK AND ENERGY Learning Intentions and Success Criteria Learning Intentions To learn about the Physics definition of “work” To learn how to calculate work To learn about the different types of energy To learn about the “Law of Conservation of Energy” Success Criteria I can define the P...

WORK AND ENERGY Learning Intentions and Success Criteria Learning Intentions To learn about the Physics definition of “work” To learn how to calculate work To learn about the different types of energy To learn about the “Law of Conservation of Energy” Success Criteria I can define the Physics term of “work” I can calculate work using the correct equations I can describe some of the different types of energy that affect motion I know what the “Law of Conservation of Energy” is and explain what happens to energy Work Work happens whenever things are moved or rearranged by force Work is a scalar quantity Work = force applied x distance moved oW = F x d Energy Energy will: ◦Make things move ◦Make things burn ◦Make light and sound ◦Make things happen We can’t see “energy”, but we can see what it can do!  The Definition of Energy Energy is It is the ability measured to do work in joules (J) What sort of things have energy? BRICKS AND A PULLEY A pile of bricks is lifted higher by a person using a pulley. What has the energy to do this? ROCK AND EXPLOSIVE An explosive is placed in a hole drilled into rock. The rock explodes into pieces. What has the energy to do this? JACK IN THE BOX Open the lid of a jack-in-the-box. What happens? What has the energy to do this? WIND MILL The vanes on a windmill turn around. What had the energy to do this? GLOBE AND BATTERY A light globe glows brightly when the power is switched on. What has the energy to do this? In all the above cases, ENERGY made something happen. Although we couldn't see the energy, we could see what it did. 1. In the bricks and pulley, the man had the energy to pull the bricks up. 2. In the rock and explosive, the explosive had the energy. 3. In the jack-in-the-box, the spring has the energy. 4. In the windmill, the wind had the energy. 5. In the light globe, the battery had the energy. DIFFERENT TYPES OF ENERGY https://www.youtube.com/watch?v=zVRH9d5PW8g Energy Transfers and Changes Energy often changes from one type to another. For example, in the Jack-in-the-box, energy is stored in the compressed spring as elastic potential energy. When the Jack jumps, the potential energy becomes kinetic energy. We can represent this energy change as shown below. The arrow means “changes to”. Potential Energy  Kinetic energy Energy Transfers and Changes ◦An electric light, when it is turned on, changes electrical energy into light energy Electrical energy  Light energy ◦A torch when turned on changes electrical energy into light energy Electrical Energy  Light energy ◦When a nail is hammered into a block of wood, the nail gets warm Kinetic energy  Heat Energy  Example for Energy Transfers and Changes An energy converter changes energy from one type into another. 1. Which of the energy converters: i. Chemical  Kinetic ii. Electrical  Thermal iii. Chemical  electrical iv. Electrical  Radiated v. Electrical  Sound Energy There are lots of different types of energy. We will be looking at the following types more closely: oKinetic Energy oGravitational Potential Energy oElastic Potential Energy Kinetic Energy Kinetic Energy (KE) is the energy possessed by moving objects Kinetic Energy = ½ x mass x speed squared ◦ KE = ½ x m x v2 ◦ Mass is in ‘kg’, speed is in ‘m/s’ and KE is in ‘J’ Gravitation al Potential Energy GPE is the energy possessed by objects dependent on their position in gravitational field. Gravitational Potential Energy = mass x gravitational field strength x height ◦ GPE = m x g x h ◦ m is the mass of the object in “Kg”, ◦ g is the Gravitational Field Strength, with the units in ‘9.8 N/kg’, ◦ And h is the height in is in ‘m’ Elastic Potential Energy EPE is the energy possessed by stretched or compressed objects Elastic Potential Energy = ½ x spring constant x extensions/compression squared ◦ EPE = ½ x k x e2 ◦ k is the spring constant, a measure of how ‘stiff’ the object is and it has the units ‘N/m’, ◦ e is the extension/compressi on, with the units in ‘m’, ◦ and EPE is in ‘J’  Example of Speed Affecting KE ◦ A car with a mass of 1400 kg is travelling at 40 km/hr. What is its KE (Kinetic Energy)? 1.Convert the speed to m/s Speed = 40 ÷ 3.6 = 11.1 m/s 2.KE = ½ x m x v2 = ½ x 1400 x 11.12 KE = 86 247 J or 86 kJ (1000 J = 1 kilojoule or kJ) Your Turn Make the same car travel twice as fast, at 80 km/h. What is the kinetic energy now?  ANSWER KE = 344988 J or 345 kJ. The car now has four times as much Kinetic Energy. WORK AND ENERGY EXPLAINED https://www.youtube.com/watch?v=zVRH9d5PW8g  LAW OF CONSERVATIO N OF ENERGY This is a scientific law of that states the total energy in a system is always constant and cannot be created or destroyed. LAW OF CONSERVATION OF ENERGY EXPLAINED https://www.youtube.com/watch?v=OTK9JrKC6EY https://www.youtube.com/watch?v=VxCORJ8dN3Y