HPS ENERGY NOTES PDF - Honors Physical Science

Machines, Work, and Energy Notes Honors Physical Science Energy is the ability to cause change, or do work. A Machine changes the force or increases the motion from work. Can you lift a grand piano? Nope. But you can push it up a ramp or lift it with a pulley sys...

Machines, Work, and Energy Notes Honors Physical Science Energy is the ability to cause change, or do work. A Machine changes the force or increases the motion from work. Can you lift a grand piano? Nope. But you can push it up a ramp or lift it with a pulley system. TYPES OF MACHINES Simple Machines do work with only one movement of the machine. There are six types of simple machines: Lever, Pulley, Wheel and axle, inclined plane, screw, and wedge. Compound machines are combinations of two or more simple machines. - Scissors are two levers and two wedges. Efficiency of a machine is the ratio of input work to output work. Output work (Joules) Efficiency == Input work (Joules) X 100 The best way to increase efficiency is to reduce friction. USEFULNESS Bicycles increase speed. Wedges change the direction of force: Car jacks increase force, but decrease speed. The up force provided by the jack is greater the down force that you apply to the jack, but you move the jack handle a lot faster than the jack lifts the car. MECHANICAL ADVANTAGE MA = Fo / Fi where output force (N) is divided by input force (N) WORK transfers energy - Tennis racquet transfers energy to the ball. So if energy is transferred via work, and energy is measured in Joules, then work can also be measured in Joules. If the racquet dow 250 Joules of work on the tennis ball, then 250 joules of energy are transferred to the ball. Systems are anything around which you can imagine a boundary. The system can be a single object (Racquet,) or a group of objects…like the solar system.  Machines, Work, and Energy Notes Honors Physical Science Is chemical energy from the food you eat the same as chemical energy from the Sun or from gasoline? Energy is like money. Money exists in many different forms….coins, dollar bills, $20 bills, checks, etc. You can convert money from one form to another. Coins to bills, bills to checks. In any case, it is still worth the same amount. Same for energy. Energy from the sun and energy from food are different forms of the same thing. Kinda like Ice, water, and steam. KINETIC ENERGY Kinetic Energy is energy in motion. Energy due to Motion. Kinetic energy depends on the mass and velocity (Speed) of an object. KE = ½ MV2 where M is Mass and V is velocity KE is measured in Joules (J) Try this: A jogger with a mass of 60 Kg is moving at 3 m/s KE = ½ 60 Kg X 3 m/s2 KE = 30 X 9 KE = 270 J POTENTIAL ENERGY Potential Energy is the energy stored in an object at rest. U=mgh Where m is mass, g is acceleration due to gravity (9.8), and h is height. (Practice sheets on calculating U and KE) LAW OF CONSERVATION OF ENERGY Forms of energy: Radiant: From sun and bulbs Thermal: heat from sun, fire, etc Electrical: From outlets, powerplants, lightning Sound: many noises Nuclear: sun (fusion), nuclear power plants, nuclear decay Electromagnetic: Waves on Electromagnetic Spectrum Transfers of Energy: Electrical → light, sound Chemical → light, sound, thermal Solar → chemical (photosynthesis), electrical Kinetic → sound (guitar, crash)  Machines, Work, and Energy Notes Honors Physical Science MECHANICAL ENERGY Mechanical Energy is the total amount of potential energy and kinetic energy contained in a system. Mechanical energy remains constant due to the Law of Conservation of Energy. POWER Power is the rate at which energy is converted. Power = Energy divided by time E = E/t Power is measured in Watts, Energy in Joules, and time in seconds. 1 Watt = 1 Joule/Second A 13 Watt light bulb converts 13 Joules of electric energy into 13 into 13 joules of radiant energy every second. Energy conversions in your body Chemical energy in food in generally married in Calories. It is used for cellular processes. 1 Calorie is equal to 4,000 Joules 1 g of Fat is equal to 10 Cal or 40,000 Joules 1 g Carbs or Proteins is equal to 5 Cal, or 20,000 Joules SHOW POWER/WORK POWERPOINT Thermal Energy is the sum of the potential energy and kinetic energy of the particles in an object. – Thermal energy increases and mass increases – Thermal energy increases and heat increases Temperature is a measure of the average kinetic energy of the particles in an object. (the higher the energy, the faster the particles move) How do you know if someone has been sitting in your chair? (it is warm) Energy has transferred from their body into your chair. **Thermal Energy ALWAYS flows from higher temperature objects into lower. HEAT (Q) is the transfer of energy from one object to another (Measured in Joules). There is no such thing as cold….just the absence of heat (energy). Why does it feel cold outside today? Because the heat is ruching from you 98o into the cold air. Conduction is the transfer of energy through matter by direct contact of the particles. Solids are the best conductors of heat because the particles are close together.  Machines, Work, and Energy Notes Honors Physical Science Convection is the transfer of energy through the movement of heated particles. Hot particles rise while cooler particles fall. This cannot happen in solids, only liquids and gases. (Convection Currents) Radiation is the transfer of energy through a vacuum via electromagnetic waves. This happens fastest in a vacuum, but can happen through matter…..fastest in gases. DOES NOT REQUIRE A MEDIUM. MATERIALS Some transfer heat well, some do not. Conductors allow heat to flow easily (metals, skin) Insulators DO NOT allow easy flow of heat. (wood, styrofoam, plastic, fiberglass) SPECIFIC HEAT Specific Heat is the amount of energy needed to raise i Kg of a substance 1o C or K – Specific to different types of material or substance. – Measured by a colorimeter Q = mcΔT where Q is heat, M is mass, c is specific heat and 𝝙T is change in temperature. For specific Heat, the formula is c = Q. M x 𝝙T RESISTANCE Resistance is the tendency for a material to resist the flow of electrons, and to convert electrical energy into other types of energy, such as heat. This is why laptops, cell phones get hot after you have used them for a while. ALMOST all materials have at least SOME resistance. The resistance of long copper wires can affect current through a circuit. OHM’S LAW The current in a circuit is equal to the voltage divided by resistance. I = v/r Where I is Current, v is voltage, and r is resistance Current is measured in Amperes (A), Voltage is Measured in Volts (V), Resistance is measured in Ohms (𝝮). Alternating Current (AC) Changes the direction of the current 120 times per second. Direct Current (DC) is a one-way current and does not change direction.  Machines, Work, and Energy Notes Honors Physical Science Series and parallel Circuits Series circuits have only one branch. The parts are wired together, one after another. Parallel Circuits contain two or more branches for current, and each branch can be turned on and off separately. There can be current through all, any, or none of the branches. Because they all connect to the same points, the voltage difference of each branch is the same. SO, according to Ohm’s Law, the current is greater through the branches with lower resistance. Household circuits are combinations of series and parallel, but are mostly parallel. The US voltage difference in standard home outlets is 120 V. For large appliances such as the refrigerator and the clothes dryer, the outlets have a voltage difference of 240 V. Electrical Power is Current times voltage P = IV Current is in Amps, Voltage is in volts, and Power is measured in Watts. Energy of Chemical Reactions ALL Chemical reactions absorb and release energy. Chemical bonds are the source of most of that energy. That is, chemical bonds contain a lot of energy. When reactions occur, chemical bonds are broken, the atoms rearrange, and new bonds are created. Breaking bonds takes a lot of energy, so energy is absorbed to break those bonds. Shen new bonds are created, a lot of energy is released. Many of the reactions that you are familiar with release more energy than is absorbed. These are called Exergonic reactions. In these reactions, If the energy that is released is in the form of heat energy, the reaction is termed to be an exothermic reaction. (Fire, Fireworks, Explosions) C6H12O6 + 6O2 = 6CO2 + 6 H2O Wood combustion reaction  Machines, Work, and Energy Notes Honors Physical Science Other reactions absorb more energy than they release. These are called endergonic reactions. Again, if the energy that these reactions are releasing is heat energy, then that reaction is termed an exothermic reaction. Often times electricity is the energy used to keep these reactions going. 2H2O(aq) + Electricity → 2H2(g) + O2(g) + energy CONSERVATION OF ENERGY IN CHEMICAL REACTIONS You already learned that energy cannot be created or destroyed. The same is true during chemical reactions. ENERGY OF + ENERGY = ENERGY OF + ENERGY REACTANTS ABSORBED PRODUCTS RELEASED