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Chapter 9 Notes I. Work, Power, and Machines A. What is _____? 1. measures the effect of a ______ 2. must act over a _________ 3. lots of force can be ________, but __ work done how? 4. formula: 5. work is measured in ______ SI Unit Math Skills B. Power 1. measures the _____ at which _____ is done 2. determined by how _____ or _____ work is completed 3. formula: 4. power is measured in ______ SI Unit Math Skills C. Machines and mechanical advantage 1. machines ____ us do work by ____________ the work that we ____ ____ them a. machines can ______ the __________ of a force b. machines can greatly _______ an ______ force by changing the ________ over which the ______ is applied 2. different _______ can do the _____ amount of work a. lifting a box straight up requires a ______ force over a ______ distance b. using a ramp to lift a box requires a ________ force over a ________ distance 3. mechanical advantage tells how much a machine __________ force or ___________ distance a. MA is a ratio between ______ and ______ forces b. formula: c. __ SI Unit it is a ______ d. HINT: all answers should be ________ than ____ Math Skills II. Simple Machines A. Broken down into ____ main categories 1. the ______ family 2. the _________ ______ family B. The ______ family 1. levers are divided into three classes a. 1st class b. 2nd class c. 3rd class 2. ________ are modified levers a. single fixed pulley _________ b. single moveable pulley _________ c. multiple pulleys even higher mechanical advantage d. hint: look at the ________ of ________ force ropes bearing the load e. multiple pulley systems are often called a ______ ____ _______ 3. a ______________ is a lever or pulley connected to a shaft a. wheel turns axle also turns b. small input force large output force c. example: steering wheel of a car C. The _____________ family 1. inclined planes __________ and _________ force a. changes __________ and ___________ of force b. example: wheelchair ramp 2. a _______ is a modified inclined plane a. functions like two inclined planes back to back b. ____ ___________ force becomes ____ forces directed out to the ______ c. example: axe blade 3. a screw is an inclined plane wrapped around a ___________ a. threads of a screw inclined plane b. _________ threads more _______ force required D. Compound machines 1. machine made up of more than one simple machine 2. examples: a. pair of scissors two ___________ joined at a _________; each lever has a _______ for a blade b. car jack _____ in combination with a large ______ III. What is Energy? A. Important Concepts 1. whenever _____ is done, _______ is transferred or transformed to another system 2. energy can be present in an object or system even when nothing is happening 3. because ______ is a measure of the _______ to do _____, energy and work are both expressed in _______ B. Potential energy 1. observations a. stretching a rubber band requires _____ b. releasing a stretched rubber band ___________ c. energy used to _______ the rubber band is ______ in the rubber band able to do _____ at a ______ time d. where is the energy before you release it? 2. potential energy is ______ energy a. common names include: 1) _______ energy 2) energy of _________ 3) energy of ____ b. types of potential energy 1) ________ potential energy ____________ 2) __________ potential energy ____________ 3) _________ potential energy _________/ _______________ 3. gravitational potential energy depends on both _____ and _______ a. because it results from the ______ of ________, GPE depends on the _____ of the objects in a system and on the _________ between them b. formula: c. note that GPE is measured in _______ SI Unit d. also note that “mg” in the equation is the _______ of the object _____ = _______ x _______ Math Skills C. Kinetic energy 1. observations a. apple falls from the branch of a tree ________ to do _____ b. energy of a moving object _______ 2. kinetic energy depends on _____ and _____ a. falling apple > falling cherry Why? b. apple falls kinetic energy _________ Why? c. formula: 3. kinetic energy depends on ______ more than mass a. because speed is ________, a greater value for speed will cause a ______ increase in KE b. example: violence of a car crash Math Skills D. Other forms of energy 1. mechanical energy a. sum of _________ and _________ energy b. ___ = ___ + ___ 2. atoms and molecules have kinetic energy a. all atoms are ___________ in motion b. can be affected by ____________ 3. chemical reactions involve __________ energy 4. living things get energy from ________ 5. the sun gets energy from ______ reactions ______ _____ 6. ___________ is a form of energy 7. ______ can carry energy across empty space IV. Conservation of Energy A. Energy transformations 1. ________ energy can become _______ energy 2. _______ energy can become _________ energy 3. energy transformations explain several everyday occurrences a. a _________ ball b. the ________ of a ball 4. mechanical energy can change to other forms of energy a. elastic PE ________ energy b. heat energy result of _______ (___) B. The law of conservation of energy 1. energy cannot be ________ or __________ 2. energy does not simply ________ or _________ 3. systems may be _____ or _______ C. Efficiency of machines 1. not all of the work done by a machine is ________ work a. _______ _____ b. _______ 2. efficiency is the ______ of useful work to work in a. ___ SI unit b. formula: c. ___ machine is _____ efficient Math Skills