1. ENERGY,WORK, POWER, AND MACHINES IPC Spring 2008

2. Energy, Work, Power & Machines 1. Energy is the ability to do work. Potential energy – stored energy or energy due to position Potential energy – stored energy or energy due to position PE=m g h PE=m g h m is mass (kg) m is mass (kg) g is gravity (9.8 m/s 2 ) g is gravity (9.8 m/s 2 ) h is the height of the object (m) h is the height of the object (m)

3. Energy, Work, Power,& Machines Kinetic energy – energy of motion Kinetic energy – energy of motion KE=1/2 mv 2 KE=1/2 mv 2 m is mass (kg) m is mass (kg) v is velocity (m/s) v is velocity (m/s)

4. Energy, Work, Power, & Machines 2.Energy conversion is a changing of one form of energy to another. 2.Energy conversion is a changing of one form of energy to another. 3.The Law of Conservation of Energy states that energy cannot be created nor destroyed, but is only changed from one form to another. 3.The Law of Conservation of Energy states that energy cannot be created nor destroyed, but is only changed from one form to another.

5. Energy, Work, Power, & Machines 4.Work is done when a object moves through a distance because of a force acting upon the object. 5.The following formula is used to calculate work: W=Fd. W stands for the work done (J) F stands for the force (N) d stands for distance (m) The SI unit for work is the joule (J). The SI unit for work is the joule (J).

6. Energy, Work, Power, & Machines 6.Power - the rate at which work is done. 7.Power can be calculated by using the following formula: P= Wor P = F d t P stands for power (W) W stands for work (J) t stands for time. (s) The SI unit for power is the watt (W).

7. Energy, Work, Power, & Machines 8.A simple machine is a device that changes the size or the direction of force that is being used to do work. 9.The six classes of simple machines are: inclined planes, wedges, screws, levers, pulleys, and wheels and axles.

8. Energy, Work, Power, & Machines 10. An inclined plane is a machine that has a sloping surface that is longer than its vertical side. 11. A wedge is a modified inclined plane. It has a thin or sharp end and a thicker end. A screw has spiral threads wound around a cylinder. The screw is a spiral inclined plane.

9. Energy, Work, Power, & Machines 12.A lever is a bar that pivots around a fixed point called a fulcrum. There are three classes of levers, based on the positions of the effort force, resistance force and fulcrum. Fulcrum in the middle= 1 st class lever Resistance in the middle= 2 nd class lever E Effort in the middle= 3 rd class lever

10. Energy, Work, Power, & Machines 13.A pulley is a machine that changes the direction of a force. A pulley is made up of a rope that turns around a wheel. A wheel and axle is a machine that has a larger effort wheel and a small resistance wheel that turn around the same pivot.

11. Energy, Work, Power, & Machines 14.The mechanical advantage is the number of times a machine multiplies an effort force. Mechanical advantage can be calculated by the following equations: AMA = F r IMA = d e F e d r AMA = actual mechanical advantage (real life) IMA = ideal mechanical advantage (pretend) F r = resistance forced e = effort distance F e = effort forced r = resistance distance

12. Energy, Work, Power, & Machines 15.The mechanical advantage of a pulley system is determined by counting the number of strands of rope that support the resistance force.

13. Energy, Work, Power, & Machines 16.Work input is always greater than work output due to friction. W in = W out F e x d e = F r x d r W in = work input (J) W out = work output (J) F e = effort force (N) d e = effort distance (m) F r =force of the resistance (N) d r =how far the resistance moved (m)

14. Energy, Work, Power, & Machines 17.Efficiency is a measure of how much of the work put into a machine is changed to work put out by the machine. Efficiency is calculated using the following formula: efficiency = W out x 100% W in efficiency =AMAx 100% IMA

15. Energy, Work, Power, & Machines 18. Compound machines consist of two or more simple machines.