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Name:________________________________ Period:____________ 4.2 Energy and the Conservation of Energy Part 1 (pg. 83-87) Energy Defining Energy ________________ is one of the fundamental quantities in our universe. Without energy, _______________ could ever change. Yet energy itself __________________ be directly smelled, _________________, touched, seen, or _________________. Energy appears in many forms, such as _____________ and _____________. Energy can travel in different ways, such as in ______________ and _____________ waves and in electricity. The workings of the ___________________________ (including all of our man-made technology) can be viewed from the _________________________ of energy flowing from one place to _____________________ and changing back and forth from one ___________ to another. Energy is a ______________ that measures the ability to cause _____________. Energy can cause changes in temperature, ____________, position, momentum, _________________, or other physical variables. Energy can also ______________ change in materials, such as __________________ wood changing into ashes and smoke. Energy is a quantity that ____________________ the ability to cause ______________ in a physical system. Examples Units of Energy A gust of wind has ______________ because it can move objects in its path. A piece of ______________ in a fireplace has energy because it can ________________ heat and light. You have energy because you can _______________ the motion of your own body. Batteries have energy because they can be used in a radio to make _________________ ______________________ has energy because it can be ______________ in an engine to move a car. A ball at the top of a hill has energy because it can ___________ down the hill and ____________ objects in its path. The unit of measurement for energy is the ______________. One joule is the ______________ needed to push with a force of 1 _____________ over a distance of 1 meter. The joule can be abbreviated as _____ or as Newton-meter (Nm), which means 1 newton multiplied by 1 meter. If you ___________ a pen with a force of 1 newton for a distance of 1 ________________ across a table, 1 joule of Work means different things What work means in physics Work is done on objects your _____________ is converted into the energy of the pen’s motion. The word work is used in many _______________________ ways. You should always _______________ over your work before handing in a test. You _____ to work. Your toaster doesn’t ___________. You work with other ____________________ on a group project. In physics, work has a very specific meaning. Work is the _______________ of energy that results from applying a force over a distance. To calculate work, you _______________ the force by the distance the object moves in the direction of the _________________. If you lift a block with a weight of 1 newton for a distance of 1 ____________, you do 1 joule of work. One _____________ of energy is transferred from your ___________ to the block, changing the block’s energy. Both work and ______________ are measured in the same units because work is a form of __________________. When thinking about work, you should _________________ be clear about which force is doing the work on which __________________. Work is done ______ objects. If you lift a block 1 meter with a force of 1 ________________, you have done 1 joule of work on the ______________. Stop here and wait for further instructions from Mrs. Nipper Looking For…. Givens… Work Force and Distance Equation…. Units for answer… F=W÷d M (meters) Practice Problems for Work 1) Angel uses 20N of force to push a lawn mower 10 meters. How much work does she do? 2) Sean uses 45N of force to stop the cart 1 meter from running his foot over. How much work does he do? 3) Aaron does 15 Joules of work to push the pencil over 1 meter. How much force did he use? 4) Desaree uses a force of 25 Newtons to lift her grocery bag while doing 50 Joules of work. How far did she lift the grocery bags? 5) The baseball player does 1234 Joules of work when hitting a baseball into left field. Assuming the baseball landed 100 meters away from home plate, how much force did the player use to hit the ball? Potential Energy What is Potential Energy? Gravitational Potential Energy How to calculate potential energy ______________________ energy is energy due to position. The word potential means that something is _____________ of becoming something else. Systems or objects with potential _______________ are able to exert forces by exchanging energy as they change. For example, a _______________ spring will use this energy to move itself and anything attached to it back to its ______________________ length. A block above a ______________ has potential energy. If released, the force of _________________ moves the block to a position of ________________ energy. The term gravitational potential energy describes the energy of an ________________ object. The term is often shortened to just “potential energy” because a common type of potential energy in ______________ problems is gravitational. Unless otherwise stated, you can assume “potential energy” means ______________________ potential energy. How much potential ___________ does a raised block have? The block’s potential energy is exactly the ________________ of work it can do as it goes down, which is _____________ to the amount of work done to lift it up to its _________________. Work is force ___________________ by distance. The force is the weight (mg) of the block in ____________________. The distance the ______________ can move is its height (h) in meters. Multiplying the weight by the ________________ gives you the block’s potential energy at any given height. Stop here and wait for further instructions from Mrs. Nipper Solving for… Potential Energy (Ep) Givens… Gravity (10 m/s/s) Mass height Equation… Ep=m·g·h Mass M=Ep ÷ (g·h) height H= Ep ÷ (g·m) Unit for answer… J (joules) If the roller coaster car in this picture has a weight (m·g) of 400 N, what is the potential energy of the car at each point? a. Ep= b. Ep= c. Ep= Practice Problems 1. Determine the amount of potential energy of a 5.0-N book that is moved to three different shelves on a bookcase. The height of each shelf is 1.0 m, 1.5 m, and 2.0 m. (remember that g= 10 m/s/s) a. H= 1.0 m b. H= 1.5 m c. H= 2.0 m 2. You are on in-line skates at the top of a small hill. Your potential energy is equal to 1,000 J. The last time you checked, your mass was 60.0 kg. a. What is your weight in newtons? (remember: w = m·g) b. What is the height of the hill? 3. A 37 N object is lifted to a height of 3 meters. What is the potential energy of this object? 4. At what height is an object that has a mass of 50 kg, if its gravitational potential energy is 9800 J? Kinetic Energy Kinetic Energy is energy of motion Kinetic energy can do work Kinetic energy depends on mass and speed Objects that are _______________ also have the ability to cause change. Energy of ____________ is called kinetic energy. A moving billiard ball has kinetic ___________ because it can hit another billiard ball and change its motion. Kinetic energy can also be __________________ to potential energy. The kinetic energy of a _____________________ tossed upward converts into __________________ energy as its height increases. The amount of kinetic energy an object has _______________ the amount of work the object can do by _________________ force as it stops. Consider a moving skateboard and rider. Suppose it takes a force of _________ N applied over a distance of ______ meters to slow the skateboard to a stop (v=0). The kinetic energy of the skateboard and rider is ________ Joules since that is the amount of _________ it takes to stop the skateboard: 500 N · 10 m = 5,000 J. If you had started with __________ the mass—say two skateboarders—you would have to do ____________ as much work to stop them both. Kinetic energy __________________ with mass. If the skateboard and rider are moving faster, it also takes more ___________ to bring them to a stop. This means kinetic energy also increases with ____________. Kinetic energy is related to both an object’s speed and its mass. Hint: It might help to use 0.5 instead of ½, especially in your calculator. Kinetic energy increases as the square of the speed Kinetic energy _________________ as the square of the speed. This means that if you go ______________ as fast, your energy increase by _________ times (22=4). If your speed is three times as fast, your energy is _______________ times bigger (32=_______). A car moving at a speed of 100 km/h (62 mph) has four times the kinetic energy it had when going 50 km/h (31 mph). At a speed of 150 km/h (93 mph), it has nine times as much energy as it did at 50 km/h. The stopping _________________ of a car is proportional to its ______________ energy. A car going twice as fast has four times the kinetic energy and needs ____________ times the stopping distance. This is why driving at __________ speeds can be so dangerous. Stop here and wait for further instructions from Mrs. Nipper Practice Problems 1. A 1.0 kg ball is thrown up into the air with an initial velocity of 30. m/s. How much kinetic energy does the ball have? 2. What is the kinetic energy of a 2,000-kg boat moving at 5.0 m/s? 3. A car is moving with the velocity of 10 m/s and is having mass of 250 Kg. Calculate its Kinetic energy? 4. A 55 kg man runs at a speed of 4 m/s. Find his kinetic energy.