ENERGY

Energy Energy- the ability to do work SI unit: Joules

Mechanical Energy Mechanical Energy- Energy do to the position or movement of an object For example, a rollercoaster has mechanical energy in the form of both potential and kinetic energy. Explain. http://www.classzone.com/books/ml_science_share/vis_sim/mfm05_pg126_coaster/mfm05_pg126_coaster.html

Potential Energy Stored Energy / energy of position amount depends on position or condition of the object

Gravitational Potential Energy Gravitational Potential energy is greater when the object’s height is greater G. PE is greater when the object’s weight is greater

Which has more PE, a plant sitting on a 5th floor window or one sitting on a 1st floor window? Why?

PE formula PE= mass x 9.8 x height Units Mass= grams Height=meters

Example PE Problem Mass= 65 kg Height= 35 m Gravity accel= 9.8 PE= ? PE= 65 x 9.8 x 35 = 22295 Joules

PE word problem Calc. PE 1200 kg car at the top of a hill that is 42 m high M= 1200 9.8 h= 42 1200 x 9.8 x 42 = 493920 Joules

Kinetic Energy “Energy in Motion” Will change more due to velocity (bc its squared) than mass

Kinetic energy KE is greater when the speed is greater. KE is greater when the mass of the object is greater. Which is more kinetic energy a motorcycle going 35mph or an 18 wheeler going 35 mph? Why?

Kinetic Energy Formula KE= ½ mass x velocity2

Kinetic Energy Ex Problem Mass= 44 kg Speed= 31 m/s KE= ? KE= ½ mass x velocity2 22 x 961= 21142 Joules

KE Word Problem Calc KE of 1500 kg car that is moving at a speed of 700m/s KE= ½ mass x velocity2 750 x 490000 = 367500000Joules

From PE to KE

Conservation of Energy “Energy cannot be created or destroyed” changes forms The total amount of energy NEVER changes

More Forms of Energy Chemical Energy- has to do with ions, atoms, molecules, and bonds Change to another form of energy when a chemical reaction occurs Food, Wood, Gasoline, Heating oil Electrical Energy- associated with voltage and current

More Forms of Energy Thermal Energy- associated with the movement of molecules More Motion = More Heat

Sound Energy- associated with longitudinal mechanical waves

Light Energy- associates with electromagnetic waves Light, X-rays, Lasers, Gamma Rays

Nuclear Energy Energy associated with Fission and Fusion Sun and Stars Occurs only in controlled situations on earth

Energy Transformations According the Law of Conservation of Energy… Energy can change forms Energy in battery then a light turns on Potential or chemical to electrical

More Energy Transformations Plant sitting in the sun, then making food then growing Light energy to chemical energy to kinetic energy Making music playing the piano Potential to kinetic to sound

Energy Conversions

Which of the seven main forms of energy is present in each situation?

Work Work= the force exerted over a distance When work is done, energy is transferred to the object If no movement, Zero work!

When force is applied to an object and it moves, work is done, and kinetic energy is created The greater the force, the greater the kinetic energy of the object

If work is done and an object is lifted, the object gains PE The higher it is lifted, the more PE

Work Triangle Calculating Work: Work= Force x Distance SI Unit: Joules (J) = 1 Newton*Meter W D F

Example Work Problem F= 30 N d= 1.5m W= ? W= F *d 30 * 1.5 = 45 W= 45 J W D F

Example Work Problem A carpenter lifts a 45 N beam 1.2 m high. How much work is done on the beam? F= 45 N D= 1.2 m W= ? W= F * D 45 * 1.2 = 54 W= 54 J W D F

Multiple Step A dancer lifts a 45 kg ballerina overhead a distance of 1.4 m. How much work is done? F= ? D= 1.4m W= ? W= F * d 441 * 1.4 = 617.4 J W= 617.4 J 45 * 9.8= 441 N W D F

Last one The same dancer holds the ballerina overhead for 5 seconds. How much work is being done? None, no distance is being traveled.

Power The rate at which work is done SI unit: Watts (w) = 1 Joule per second Formula= Power = Work / Time W P T

Example Problem: W= 500 J T= 20 s P= ? P T P= W / T 500 / 20 = 25 P= 25 watts W P T

Example Problem # 2 F= 450 N d= 1.0 m t= 3 s W= ? P = ? P T W= F * d 450 * 1 = 450 W= 450 J P = W / t 450 / 3 = 150 watts P = 150 watts W P T

Word Problem A mover carries a chair up the stairs in 30 seconds. His work totals 300 Joules. What was his power? P = w / t 300 / 30 = 10 P= 10 watts W P T

Last one Mary runs up the stairs in 22 seconds. Carrie runs up the stairs in 27 seconds. Each girl has a work total of 240 Joules. Which has more power? Carrie W= 240 T= 27 240 / 27 = 8.89 P= 8.89 watts Mary W= 240 T= 22 240 / 22= 10.91 P= 10.91 Watts

Machines change the force that you exert in either size or direction. Simple Machine- one movement Compound Machine- more than one movement

Machines at work 2 forces involved with machines Input Force (In) – force applied to the machine Output Force (Out)- force applied by the machine to overcome resistance

Machines at Work Mechanical Advantage- # of times the machine multiplies input force MA= input force / output force MA= input / output Out MA In

Example Problem Output = 500 N Input = 20 N MA= ? MA= Output / Input 500 / 20 = 25 MA= 25 Out MA In

Another example Output = 2000 N Input= ? MA= 10 MA= Output/ Input Input= Output / MA 2000 / 10 = 200 N Input= 200 N Out MA In

Word Problem The power steering in an car has a mechanical advantage of 75. If the input force to turn the steering wheel is 49 N, what is the output force of the car’s front wheels? Output= 3675 N MA= 75 Input= 49 N Output= ? Output= MA * Input 75 * 49 = 3675 N Out MA In

2 families of Simple Machines Levers Inclined planes

Simple Machines Lever- arm that turns around a fixed point FULCRUM- fixed part

Types of Levers 1st Class 2nd Class 3rd Class classified on location Input force, Output force, and fulcrum

First Class Lever Fulcrum between Input force and Output force Can multiple force or distance Ex: Scissors, pliers, clothes pin

2nd Class Lever Output between Input force and fulcrum Multiply force Examples: Wheel Barrel

3rd Class lever Input force between Output force and fulcrum Increase distance Examples: bicep, fishing rod, hockey stick

Pulleys Modified Lever grooved wheel with a rope or chain running along the groove Single, fixed pulley has an MA of 1

Pulley Moving Pulley- has an MA of 2 Block and Tackle Pulley- multiple pulleys put together. Increases MA

Wheel and Axle Lever family 2 wheels of different sizes that rotate together Smaller wheel is called the axle

Inclined Plane Inclined Plane- a sloping surface used to raise objects (such as a ramp) you exert less input force over a greater distance

Screw and Wedge Screw- inclined plane wrapped in a spiral around a cylindrical post Ex: Wedge- inclined plane with one or two sloping slides Ex: Chisel, knives, ax blade

COMPOUND MACHINES Compound Machine- a combination of two or more simple machines Examples: Bicycle (2 wheel and axle), the axle (wedge and lever)

Efficiency in Machines With machines, not all work is useful Some lost as heat, through friction, Efficiency- measure of how much useful work a machine can do Efficiency= useful work output work input

Efficiency Problem Work input= 180 J Useful work output= 140 J