Post on 15-Mar-2016
description
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
KE ttp::: l n o :m r w:h g e c e cg a hll: om:s t s: l: r ::::::i c i e d f ee
:::::::::::::::::::::: 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?