Presentation on theme: "May 15General Science Chapter 131 Work & Energy Chapter 13."— Presentation transcript:
May 15General Science Chapter 131 Work & Energy Chapter 13
May 15General Science Chapter 132 Work Everyday concept of work. Scientific definition: Work is the transfer of energy through motion. A force applied, in which the object moves, to an object in the direction that the object moves.
May 15General Science Chapter 133 Work In order for work to take place, a force must be exerted through a distance. In order for work to be done, there has to be motion, and the motion has to be in the direction of the applied force. If there is no motion, no work will be done
May 15General Science Chapter 134 Recall “work” lab Did you do more work lifting the books to shoulder level or over your head? Greater distance means more work Did you do more work lifting 2 books or 4 books? Greater force means more work
May 15General Science Chapter 135 Work Equation Work, like energy, is measured in joules. 1 J = 1 N ∙ m.
May 15General Science Chapter 136 Work and Energy Work is the transfer of energy through motion. When 1 J of work is done on an object, 1 J of energy has been transferred to the object.
May 15General Science Chapter 137 Example A student’s backpack weighs 10 N. She lifts it from the floor to a shelf 1.5 m high. How much work is done on the backpack? Force, F = 10 N Distance, d = 1.5 m Work = (Force)(Distance) Work = (10 N)(1.5 m) Work = 15 N ∙m = 15 J
May 15General Science Chapter 138 Example #2 A dancer lifts a 400-N ballerina overhead a distance of 1.4 m and holds her there for several seconds. How much work is done on the ballerina? Work = (400 N)(1.4 m) Work = 560 J Note that the time was not important for us to determine the work done.
May 15General Science Chapter 139 Example #3 A carpenter lifts a 45-kg beam 1.2 m high. How much work is done on the beam? Remember that weight equals mass times acceleration due to gravity. Weight = (45 kg)(9.8 m/s 2 ) = 441 N Work = (441 N)(1.2 m) Work = J
Power May 15General Science Chapter 1310 The rate at which work is done. How much work is done in a given amount of time The ratio of work to time
Watts May 15General Science Chapter 1311 Power is measured in Watts, named after James Watt, who helped develop the steam engine. 1 W = 1 J/s Very small unit, so we often use kW Watts = 1 horsepower
Example May 15General Science Chapter 1312 A figure skater lifts his partner, who weighs 450 N, 1 meter in 3 seconds. How much power is required?
You try May 15General Science Chapter 1313 A N elevator rises 30.0 m in 60.0 s. How much power is required? Express your answer in kW.
Making Connections May 15General Science Chapter Joules = 1 calorie Joules are units for energy and work 1 Calorie = 1000 calories A Calorie is used for foods, so if a candy bar has 250 Calories it is the same as calories.
Example #1 May 15General Science Chapter 1315 Tommy eats a candy bar that has 230 Calories. How many Joules is that? 1 Calorie = 1000 calories 1 calorie = Joules so 1 Cal = 4184 Joules therefore 230 Calories = Joules
Example #1 continued May 15General Science Chapter 1316 How much Power can be produced with the 230 Calorie candy bar in 1 hour? 230 Cal = Joules Use the equation below
Example #1 continued May 15General Science Chapter 1317
Discussion #1 May 15General Science Chapter 1318 Define work and what are the SI units? What units are used to measure Power? Why is the unit kW used more often than W? What is the conversion factor for horsepower to Watts?
May 15General Science Chapter 1319 Machine A device that makes work easier By using a machine you DO NOT DO LESS work. It just makes it seems easier to do the work.
May 15General Science Chapter 1320 Work and machines Work is made easier by doing 1 of 3 things Changes the size of the input force Changes the direction of the force Changes both the size and the direction of the force Opening a paint can with a screwdriver Changes size – you can use less force Changes direction
May 15General Science Chapter 1321 Forces and machines Effort force (F e ) – applied to the machine The force you exert Also called input force Resistance force (F r ) – applied by the machine to overcome gravity or friction The force the machine exerts Also called output force
May 15General Science Chapter 1322 Work and machines Work input (W in ) – work done on the machine Effort force times distance it moves W in = F e X d e Work output (W out ) – work done by the machine Resistance force times distance it moves W out = F r X d r
May 15General Science Chapter 1323 Mechanical advantage The number of times a machine multiplies the effort force The ratio of output to input. (usually a force)
May 15General Science Chapter 1324 Mechanical advantage Can be greater than 1 Opening paint can Can be equal to 1 Raising blinds Can be less than 1 Hitting a baseball
May 15General Science Chapter 1325 Example A worker applies an effort force of 10 N to pry open a window that has a resistance of 500 N. What is the mechanical advantage of the crowbar? F r = 500 NF e = 10 N
May 15General Science Chapter 1326 You try A jack is used to lift a 2000-N rock. The effort force is 200 N. Find the mechanical advantage.
May 15General Science Chapter 1327 Discuss #2 A _____________ is a device that makes work easier. What are the 3 ways a machine can make work easier? What do we call the force applied to a machine? What do we call the force applied by a machine?
May 15General Science Chapter 1328 Discussion #2 What is mechanical advantage? What does it mean when the MA value is equal to 1? How do we calculate MA?
May 15General Science Chapter 1329 Simple machine A device that does work with only one movement There are six types LeversInclined Plane PulleyWedge Wheel & AxleScrew
Ideal Mechanical Advantage The ratio of output to input (usually a force) disregarding friction and gravity. When the output work = the input work. Machine would be 100% efficient, which is impossible. 5/2/2015General Science Chapter 1330
May 15General Science Chapter 1331 Levers Examples Crowbars Seesaws Baseball bat
May 15General Science Chapter 1332 Definitions A lever is a bar that is free to pivot, or turn, about a fixed point. A fulcrum is the fixed point of a lever. The effort arm is the part of the lever on which the force is applied. The resistance arm is the part of the lever that exerts the resistance.
May 15General Science Chapter 1333 Lever fulcrum Resistance arm Effort arm Effort force Resistance force
May 15General Science Chapter 1334 Mechanical advantage Review, we learned that We can also use for levers
May 15General Science Chapter 1335 You try You use a crowbar 160 cm long as a lever to lift a large rock. The rock is 20 cm from the fulcrum. You push down on the other end of the crowbar. What is the length of the effort arm? The resistance arm? What is the IMA of the lever?
May 15General Science Chapter 1336 First class levers The fulcrum is in the middle Seesaw crowbar fulcrum Resistance arm Effort arm Effort force
May 15General Science Chapter 1337 Second class levers The resistance is in the middle wheelbarrow nutcracker fulcrum Resistance armEffort arm Effort force
May 15General Science Chapter 1338 Third class levers The effort is in the middle Baseball bat broom fulcrum Resistance arm Effort arm Effort force
May 15General Science Chapter 1339 Discuss #3 What is a lever? What is a fulcrum? What is the effort arm? What is the resistance arm?
May 15General Science Chapter 1340 Discussion #3 What are the 3 types of levers? What is an example of each type of lever? Which type usually has a IMA value < 1?
May 15General Science Chapter 1341 Pulleys Pulley – grooved wheel with a rope or chain running along the groove Acts like a lever The two ends of the rope are the effort arm and the resistance arm The wheel acts like the fulcrum
May 15General Science Chapter 1342 Fixed pulley Attached to something that doesn’t move Change the direction of a force IMA of 1 LeLe LrLr FrFr FeFe
May 15General Science Chapter 1343 Movable pulley Attached to the object being moved IMA greater than 1 Effort distance must be greater than resistance distance LeLe LrLr FrFr FeFe
May 15General Science Chapter 1344 Block and tackle System of fixed and movable pulleys Has IMA equal to the number of ropes that support the resistance weight Count every rope coming off the movable pulleys that supports or moves the resistance force.
May 15General Science Chapter 1345 Examples of Block & Tackle
May 15General Science Chapter 1346 Example of Block & Tackle #2
May 15General Science Chapter 1347 Wheel and axle Consists of two wheels of different sizes that rotate together The effort force is usually applied to the large wheel The small wheel, or axle, exerts the resistance force Examples: doorknob, water faucet, gears, pencil sharpener
May 15General Science Chapter 1348 Wheel and axle Can be thought of as a lever attached to a shaft Radius of wheel is effort arm Radius of axle is resistance arm Center of axle is fulcrum
May 15General Science Chapter 1349 Inclined plane A ramp Lifting something along an inclined plane means you cover more distance than lifting it straight up, but you get to use a smaller force
May 15General Science Chapter 1350 Screw An inclined plane wrapped in a spiral around a cylindrical post. As you drive in a screw, the inclined plane slides through the wood.
May 15General Science Chapter 1351 Wedge An inclined plane with one or two sloping sides Examples Chisels Knives Axe blades The material stays in place while the wedge moves through it.
May 15General Science Chapter 1352 Wedge Thickness, T Side, S
May 15General Science Chapter 1353 Variations All six kinds of simple machines are variations of two basic machines The lever The inclined plane
May 15General Science Chapter 1354 Compound Machine A machine that is made up of 2 or more simple machines. Examples of compound machines Fishing rod, pencil sharpener, an axe
May 15General Science Chapter 1355 Discuss #4 What kind of simple machine is a ramp? What is an inclined plane wrapped in a spiral around a cylindrical post? What kind of simple machine are chisels, knives, and axes?
May 15General Science Chapter 1356 Discussion #4 What type of pulleys have a MA = 1? What is the difference between a fixed pulley and a movable pulley? What is a block and tackle? What two groups can simple machines be broken into? What is a compound machine?
May 15General Science Chapter 1357 Energy Scientific definition: Energy is the ability to cause change. Ability to do work Any sample of matter has energy if it can produce a change in itself or in its surroundings. Energy comes in many forms and will be classified as either Kinetic or Potential.
May 15General Science Chapter 1358 Energy continued Kinetic Forms Radiant (solar), thermal, electrical, wind, sound Potential Forms Gravitational, mechanical, chemical, and nuclear Energy is measured in joules (J). Named after a British scientist.
May 15General Science Chapter 1359 Kinetic energy Energy in the form of motion Amount depends on the mass and velocity of the object. Greater mass at the same velocity OR greater velocity with the same mass will have greater kinetic energy KE = ½ mv 2 5 Types (STEWS or SHEWS)
May 15General Science Chapter 1360 Solar Energy (Radiant) Electromagnetic energy that travels in transverse waves. Energy from the sun
May 15General Science Chapter 1361 Thermal Energy Heat energy, the internal energy in a substance. Caused by the vibration and movement of atoms/molecules within substances. Geothermal energy is a good example of this type of energy.
May 15General Science Chapter 1362 Electrical Energy Energy produced by the movement of electrons. Lightning and electricity are good examples of this form of energy.
May 15General Science Chapter 1363 Wind Energy (Motion) Energy produced from the movement of objects from one place to another. Do not need to see this movement, we just know there is a change in position. Wind and some forms of hydropower are good examples of this form of energy.
May 15General Science Chapter 1364 Sound Energy Movement of energy through substances using longitudinal or compressional waves. Obviously this is how we hear “things” A compressional wave is like the movement of an inch worm or an accordion.
May 15General Science Chapter 1365 Potential energy Stored energy Depends on its position/condition/height, mass and gravity 4 Types (GECN) PE = mgh m = mass, g = gravity, h = height
May 15General Science Chapter 1366 Gravitational Energy (Hydro) Potential energy of an object due to height above the earth’s surface. The higher the object is, the more potential energy it has.
May 15General Science Chapter 1367 Elastic Potential Energy (Stored) Energy stored in a spring or rubber band or anything else that stretches. The farther it is stretched, the greater its potential energy. Energy based on the position
May 15General Science Chapter 1368 Chemical Energy The energy stored in foods, fuels, and batteries. There must be a chemical reaction to get the energy out.
May 15General Science Chapter 1369 Nuclear Energy Energy stored in the nucleus of an atom. Fusion and Fission are two examples
Mechanical Energy The sum of potential and kinetic energy in a system is called mechanical energy. Think about a roller coaster or bungee jumping. May 15General Science Chapter 1370
May 15General Science Chapter 1371 Discuss #5 Energy Review Define energy What units are used to describe energy What are the 2 main forms of energy List 3 of the 4 subsets of stored energy List 3 of the 5 subsets of moving energy What is Mechanical energy?
May 15General Science Chapter 1372 Discussion #5 Why is the first hill of a roller coaster ride the highest? Where would a roller coaster be moving fastest?
May 15General Science Chapter 1373 Discussion #5b Why can you not travel in a circular loop when on a roller coaster? Is it possible for the second hill to be taller than the first hill? Explain why? When does a coaster have the most PE? When does a coaster have the most KE?
May 15General Science Chapter 1374 Conservation of Energy Energy cannot be created or destroyed but it can change from one form to another. Example – Swing Why does it stop?
May 15General Science Chapter 1375 Conservation of energy You can never get more work out than you put in If force increases, distance must decrease.
May 15General Science Chapter 1376 Internal energy The total energy of all the particles that make up a sample of matter. Includes both kinetic and potential energy of the particles. The more mass a material has, the more internal energy it has.
May 15General Science Chapter 1377 Internal energy Different materials have different internal energies even when they have the same mass and temperature. This is because the particles in the materials are arranged differently.
May 15General Science Chapter 1378 Separate energies Internal energy of a material depends on the total energy of its particles. Mechanical energy (kinetic and potential) of the material itself has no effect on internal energy.
1 st Law of Thermodynamics The net change in energy equals the energy transferred as work and heat. Q = Heat W = Work ΔU = Internal energy May 15General Science Chapter 1379
May 15General Science Chapter 1380 Efficiency Measure of how much of the work put into a machine is changed to useful work put out by the machine.
May 15General Science Chapter 1381 Efficiency Can it ever be more than 100%? How can we increase efficiency?
May 15General Science Chapter 1382 example A worker pushes a 1500 N chair up an inclined plane that is 4.0 m long and 1.0 m high. The worker exerts a force of 500 N. What is the efficiency of the inclined plane? 1 m 4 m
May 15General Science Chapter 1383 You try Using a fixed pulley, you pull the rope down 1.0 m with a force of 72 N. A 65-N object is raised 1.0 m. What is the efficiency of the pulley?