Energy

• Please take out your notebook, formula sheet and calculator.

Energy

Def: the ability to cause change

Kinetic Energy

• Def: The energy of motion • Equation to calculate Kinetic energy

– KE = ½ mv2

• The units for energy are Joules (J).

KE Videos

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:::::::::::::::::::::: tmlh

Relationships

• The more speed an object has, the more KE it will also have

• ↑ speed ↑ KE

10 m/s 20 m/s

VS

• The more mass an object has, the more KE it will also have

• ↑ mass ↑ KE

VS1000 kg 100 kg

Math Practice

• What is the KE of a baseball moving at a speed of 40m/s if the baseball has a mass of .15kg?

• KE = ½ mv2

• KE = ½ (.15kg)(402 m/s)• KE = 120 J

• What is the KE of a 1000 kg car moving at a speed of 10 m/s?

• KE = ½ mv2

• KE = ½ (1000kg)(10m/s)2

• KE = 50,000 J

• PE http://glencoe.mcgraw-hill.com/sites/dl/free/0078600510/160350/00035807.html

Potential Energy

• Def: stored energy.– Chemical potential energy – gas, food– Elastic potential energy – compressed spring,

stretched rubber band– Gravitational potential energy – anything that

can fall

GPE

• GPE can be calculated. • Mass x gravity x height• GPE = mgh• Lets practice some math!

– Get out your calculators!

Relationships

• The higher an object is, the more GPE it will also have

• ↑ height ↑ GPE

Relationships

• The more weight an object has, the more GPE it will also have

• ↑ weight ↑ GPE

More Practice

• Find the GPE of a coffee mug with a mass of .3kg on a 1m high counter top.

• GPE = mgh• GPE = (.3kg)(9.8m/s/s)(1m)• GPE = 2.94 J

More Practice

• Find the GPE of a 8000 N roller coaster car 45 m off the ground.

• GPE = mgh = wt*h• GPE = (8000N)(45m)• GPE = 360,000 J

Video

Conservation of Energy

• Energy can be neither created nor destroyed.

• It CAN be changed, or converted.• KE to GPE and back is only one example!

Forms of Energy

• Chemical – charcoal, gas, batteries• Electromagnetic – electricity, magnetism

– Light – x-rays, gamma rays, visible light• Mechanical – moving objects, KE+GPE• Nuclear – fission and fusion• Thermal or Heat – internal motion of

molecules

Examples

• Rub your hands together. What does this do?

• Is there a conversion taking place here? What is it?

• Mechanical Thermal

More Conversions

• What conversions happen in a car engine?• Chemical mechanical electromagnetic• Chemical thermal• What about a light bulb?• Electromagnetic electromagnetic and

thermal– Electricity Light

• What conversions happen when you eat?