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Bell ringer

Bell ringer. October 10, 2014 If a person lifts a box 2 meters high to place it on a shelf, have they done any work? IF they hold the box over their head without moving it, are they doing work at that moment?. P. Sci. PS Standard 6 Chapters 4 & 5 Energy & Work. Work.

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Bell ringer

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  1. Bell ringer • October 10, 2014 • If a person lifts a box 2 meters high to place it on a shelf, have they done any work? • IF they hold the box over their head without moving it, are they doing work at that moment?

  2. P. Sci. PS Standard 6 Chapters 4 & 5 Energy & Work

  3. Work • When a force causes an object to move – work is done.

  4. Work cont. Work = Force x distance Or W = F x d

  5. If the object does not move then no work is done. W = F x d If d = 0 any number times 0 is 0 so no work.

  6. The SI unit for work is joules (J) F = N d = m So W = Nm 1 J = 1kg x m2/s2 = 1 Nm

  7. Solving problems: 1. A book weighing 1.0 Newtons is lifted 2 meters. How much work is done? F= 1.0 N and d= 2m W= F x d = 1.0 N x 2m = 2. J 2. A force of 15 Newtons is used to push a box a distance of 3 meters. How much work is done? F= 15 N and d= 3 m W = F x d = 15N x 3m = 45 J 3. It takes 100 newtons to lift a rock. Work done was 1500 Joules; how far was the rock lifted? F = 100 N and work = 1500 J solve for distance D = work/ force= 1500J/ 100 N= 15 m

  8. Monday, October 13 Bell ringer: A baby has a mass of 5 kg. What is its weight in Newtons? If the baby’s mother lifts the baby 2 meters high off the floor to its crib, how much work does the mother do?

  9. Power • Power is the rate at which work is done • Power= work/time • It is measured in watts (W) or kilowatts (kW) • Example: Lifting an elevator 18 m takes 100 kJ. If doing so takes 20 seconds, what is the average power of the elevator during the process? • Work= 100 kJ • Time = 20 seconds • Power = work/ time • P= 100kJ/ 20s = 5 kW

  10. Why do we use machines? To increase force A car jack (Changes a small force over a large distance into large force over a small distance) To increase distance Oars in a row boat (you exert a large force over a short distance and other end move a large distance) To change direction Pulling back on oars pushes boat forward

  11. PROJECT • You will begin working on your project today about Machines, Work and Energy. • Go to my web site and open the Unit 3: Work and Energy page • You will find the directions for the project there • Project is DUE Monday, Oct. 20 at beginning of class.

  12. Bell RingerOctober 14 • Today you will take a short quiz • Then, you will continue reading your book and complete some assessments on your reading • After the pledge & moment of silence, please begin reading. I will direct you in a few minutes on the assessments.

  13. Bell ringer • Oct. 15 • John moves a rock 5 meters by applying a 10N force . It takes him 20 seconds to move the rock. Find the power. • D= 5 m and F = 10N and t= 20 seconds • Power= work/time • P = (F x d)/ t • P = (10N x 5 m)/ 20 s • P= 50 J/ 20 s= 2.5 Watts

  14. Energy • The ability to cause change

  15. Energy and Work • Whenever work is done, energy is transformed or transferred to another system. • Energy is the ability to do work.

  16. Remember –work is done only when an object moves. • But - energy can be present in an object or a system when nothing is happening. • However –it can only be observed when it is transferred from one object or system to another.

  17. SI Unit of Energy • Because the amount of energy transferred is measured by how much work is done – energy and work are expressed in the same unit. Joules

  18. Potential Energy AKA – Energy of Position Potential Energy is energy that is Stored. You can’t see it but you know it’s there

  19. Types of Potential Energy • Gravitational Potential Energy –Energy stored due to position (objects that are above Earth’s surface). • Chemical Potential Energy – Energy stored in chemical bonds such as food or fuel. • Elastic Potential Energy – energy stored by something that can stretch or compress such as a rubber band or spring.

  20. Kinetic Energy • Energy in motion.

  21. Note: Kinetic energy depends more on speed than on mass.

  22. Bell RingerOct. 16/17 • What is the difference between kinetic and potential energy? • You are watching a video today called “Roller Coaster Physics.” As you watch, you will answer some assessment question.

  23. Bell RingerOct. 20 • What kind of energy does a roller coaster car have at the top of a hill? • What kind of energy does it have half- way down that hill travelling at 45 miles per hour?

  24. Mechanical Energy • The sum of the Potential and Kinetic energy in a system. KE + PE = ME * The total energy in the system

  25. Law of Conservation of Energy • Energy cannot be created nor destroyed it can only be changed. • Energy can be transferred to another object/system or to another form (potential to Kinetic)

  26. Other forms of Energy • In almost every system, there are hidden forms of energy that are related to the motion and arrangement of atoms that make up the objects in the system.

  27. Electrical energy: results from the flow of charged particles or electrons. • Light energy: (electromagnetic energy) can travel through space unlike sound energy. • Thermal (heat) Energy: energy given off as heat. (friction)

  28. Solar energy: Sun gives energy to living organisms. • Nuclear Energy: The sun gets energy from nuclear reactions like nuclear fusion. • Sound Energy: related to sound waves

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