ENERGY Essential Questions : How are energy, force, work, power and machines related? In what ways does the Bible speak about power? ENERGY What must happen for work to be done? How does doing work on an object change its energy? How are work and power related? Compare and contrast potential and kinetic energy What are three ways a machine can make doing work easier? Why can’t the work done by a machine be greater than the work done on the machine?

What is work? With your table partner, hold your table off the ground while singing Jesus Loves Me together. Lift your own chair slowly up from the ground to above your head. Hold your chair above your head and quote Newton’s first law.

When were you doing work?

What is work? In science, work is the transfer of energy that occurs when a force makes an object move. A force that does not make an object move does no work. To calculate work, multiply the force applied to the object by the distance the object is moved by that force. The unit for work and for energy is the joule (J).

7.When the applied force and the motion of the object are NOT in the same direction, the applied force is like two forces acting on the object at the same time. Hutchings Photography/Digital Light Source

5. The work done on an object depends on the direction of the force applied and the direction of the motion. 6. If force and the motion are in the same direction, calculate work by multiplying the force and the distance.

8.When the applied force and the motion of the object are NOT in the same direction, only the horizontal part of the applied force is used to calculate work . 9.The vertical part of the applied force does no work on the suitcase. 10. The work done to lift an object equals the weight of the object multiplied by the distance it is lifted.

A student lifts a 50 N bookbag 2 meters off the floor A student lifts a 50 N bookbag 2 meters off the floor. Was work done and if so how much? A weightlifter holds a 600N barbell over his head for 60 seconds. Was work done and if so how much? A boy pushes forward with a force of 125 N moving a suitcase forward 35 meters. Was work done and if so how much?

Work and Energy 11. Doing work on an object transfers energy to the object. 12. Work done when you lift an object also increases the object’s energy. Hutchings Photography/Digital Light Source

What is power? What is “rate?” 13. The rate at which work is done is known as POWER. 14.You can also think of power as how fast energy is transferred to an object. 15. You can calculate power by dividing the work done by the time needed to do the work. 16. Formula P= W÷t Power equals Work divided by time. 17. Watt is the unit for Power? EXACTLY!!

SOLVE IT! 18. When doing a chin-up, a physics student lifts his 42.0-kg body a distance of 0.25 meters in 2 seconds. What is the power delivered by the student's biceps? Work=Force x distance Power = Work ÷ time This Photo by Unknown Author is licensed under CC BY-NC-ND

What is a machine? 19. A machine is any device that makes doing something easier. 20. Machines can be simple or complex. 21. Machines make tasks easier, but don’t decrease the amount of work required. 22. A machine changes the way in which the work is done. Gabe Palmer/Alamy

23. A machine can make work easier in 3 ways: 1)by changing the size of the force, 2)the distance the force acts, 3)the direction of a force. The McGraw-Hill Companies

Efficiency? 24. The efficiency of a machine is the ratio of the output work to the input work. (Friction, an opposing force, takes away from kinetic energy and therefore-work output!) 25. Because output work is always less than input work, a machine’s efficiency is always less than 100 %. 26. The efficiency of a machine is increased when a lubricant coats moving parts.

Potential and Kinetic Energy The ability to do work The ability to move or cause change in matter Unit is…Joule! Two types of energy Potential -stored Kinetic – moving (found in all objects) © KeslerScience.com

Potential and Kinetic Energy B C D Which ball has the greatest potential energy? Which ball has the greatest potential Energy? © KeslerScience.com

Potential Energy (Gravitational) 5. The amount of PE is determined by its height and mass. 6.The higher an object or the greater it’s mass, the greater its PE 7. GPE =Weight x Height above ground Kinetic Energy 8. The energy of motion 9. Can be transformed into other types of energy 10. SI unit Joule (J) 11. Speed/velocity and mass determine its measure. 12. Found in all objects KE = 1/2 x Mass x Speed2 © KeslerScience.com

Potential and Kinetic Energy Transformation of Energy Bouncing Ball Several energy transformations happen when a ball is dropped on surface and bounces up again. PE - maximum KE - none PE – none KE - maximum PE - decreasing KE - increasing PE – maximum Ask the students to predict what the next ball in this sequence would be in terms of KE and PE. © KeslerScience.com

Potential and Kinetic Energy Transformation of energy Roller coaster © KeslerScience.com

What is thermal energy? 13. All matter is made up of trillions of atoms that are constantly moving. 14. Because particles are in motion, they have kinetic energy. 15. The faster particles move, the more kinetic energy they have. 16.Thermal energy is the sum of the kinetic energy and the potential energy of the particles that make up a material.

18. Thermal energy describes the energy of the particles that make up a solid, liquid, or gas. 17.Mechanical energy describes the energy of one object.

What is temperature? Scientists define temperature in terms of kinetic energy. Temperature represents the average kinetic energy of the particles that make up a material.

Temperature and thermal energy are related, but they are NOT the same. The particles that make up liquid and solid water have different potential energies and, therefore, different thermal energies.

Thermometers Thermometers are used to measure temperature. Common temperature scales are Celsius (°C), Kelvin (K), and Fahrenheit (°F).

The movement of thermal energy from a warmer object to a cooler object is called heat. All objects have thermal energy; however, you heat something when thermal energy transfers from one object to another. The rate at which heating occurs depends on the difference in temperatures between the objects.

Radiation- transfers thermal energy by electromagnetic waves. can travel through space (travels in a vacuum) Radiation transfers thermal energy through solids, liquids, and gases.

Lesson 3 – LR1 What are levers, wheels and axles, inclined planes, wedges, screws, and pulleys examples of? A. complex machines B. compound machines C. idea machines D. simple machines

Lesson 3 – LR2 Which uses less force to raise an object compared to lifting the object straight up? A. fulcrum B. inclined plane C. screw D. wheel

Lesson 3 – LR3 Which is a simple machine consisting of a grooved wheel with a rope or cable wrapped around it? A. gear B. pulley C. screw D. wedge

Chapter Review – MC1 What two things must you know to calculate work? A. distance and length B. force and distance C. force and power D. height and weight

Chapter Review – MC2 What do you divide work by to calculate power? A. distance B. force C. time D. weight

Which refers to the force you apply to a machine to make it work? A. energy B. input force C. output force D. power

What does a machine apply to an object? A. output power B. output force C. mechanical advantage D. input force

What does a lever rotate around? A. axle B. fulcrum C. screw D. wedge

What is transferred when work is done? A. distance B. energy C. force D. power

The work done on an object depends on the direction of the force applied and which of these? A. power B. force of the motion C. distance of the motion D. direction of the motion

What is the ratio of a machine’s output force to its input force? A. efficiency B. equal output C. mechanical advantage D. output work

When you lift an object, what else are you doing? A. decreasing the object’s energy B. increasing the object’s energy C. making the object do work D. receiving the object’s energy

Which is the rate at which work is done? A. energy B. force C. power D. work

Lesson 1 – LR3 To calculate the work done lifting an object, which is multiplied by the weight of the object? A. distance the object is lifted B. energy used to lift the object C. force applied to the object D. power needed to lift the object

Lesson 2 – LR1 Which is the product of the output force and the distance over which the output force is applied? A. machine B. input work C. output work D. mechanical advantage

Lesson 2 – LR2 How can a machine NOT make work easier? A. change the direction of the input force B. decrease the input force C. increase the amount of work done D. increase the input force

Lesson 2 – LR3 Which refers to the ratio of a machine’s output work to its input work? A. efficiency B. input force C. mechanical advantage D. output force