Energy Chap 4 Intro & Conservation. The Nature of Energy 4.1.
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Transcript of Energy Chap 4 Intro & Conservation. The Nature of Energy 4.1.
EnergyEnergy
Chap 4
Intro & Conservation
The Nature of EnergyThe Nature of Energy
4.1
What is Energy?What is Energy?
Every change that occurs (large or small) involves energy.
Changes are always taking place – light bulbs are heating the air the wind might be rustling leaves cars are driving down the road
What is Energy?What is Energy?
Energy is the ability to cause change. Anything that causes change must
have energy.The SI unit for energy is the joule
(abbreviated J)
Nature of EnergyNature of Energy
ENERGY
motion of electric charges
bonding of atoms
motion of objects
internal motion of particles
changes in the nucleus
The ability to cause change.
MECHANICAL
ELECTRICALCHEMICAL
NUCLEAR
THERMAL
joules (J)
An Energy AnalogyAn Energy Analogy
If you had $1000, you could put it in your wallet put it in the bank trade it for gold exchange it for travelers’ checks
Regardless of its form, money is money.
An Energy AnalogyAn Energy Analogy
In the same way, energy is energy – regardless of its form. Energy from the Sun that warms
you and energy from the food that you eat are only different forms of the same thing.
Nature of EnergyNature of Energy
Kinetic Energy (KE) energy a moving object has because
of its motion depends on mass and velocity
Nature of EnergyNature of Energy
KE = ½ mv2
KE increases as mass increases KE increases as speed increases
80 km/h
50 km/h
80 km/h80 km/h truck
50 km/h motorcycle
• Which has the most KE?
• Which has the least KE?
Nature of EnergyNature of Energy
Potential Energy (PE) stored energy depends on position or configuration
of an object
Nature of EnergyNature of Energy
• Which boulder has greater gravitational PE?
• What other ways can an object store energy?
PE = mgh PE increases as mass increases PE increases as height increases
Potential EnergyPotential Energy
There are several types of PE: Elastic PE
•Stretched rubber band Chemical PE
•Gasoline (bonds) Gravitational PE
•anything that can fall
• increases with height and mass
KE or PE?KE or PE?
An apple in a tree has PE.
An apple falling from a tree has KE.
Conservation of EnergyConservation of Energy
4.2
Conservation of EnergyConservation of Energy
Law of Conservation of Energy Energy can change from one form to
another, but the total amount of energy never changes.
6 Forms of Energy6 Forms of Energy Mechanical Thermal Energy Chemical Energy Electrical Energy Electromagnetic Energy Nuclear Energy
Transforming EnergyTransforming Energy
Light bulbs transform electrical energy into light and heat.
Transforming EnergyTransforming Energy
An engine transforms the chemical PE stored in gasoline molecules into the kinetic energy of a moving car or bus. spark plug fires (chemical PE into
thermal energy) Hot gases expand (thermal
energy into kinetic energy)
Transforming EnergyTransforming Energy
Some energy transformations are less obvious (no visible motion, sound, heat, or light)
Green plants convert light energy from the Sun into energy stored in chemical bonds in the plant
Conservation of EnergyConservation of Energy
PE KE The form of energy changes, but
the total amount of energy remains the same.
View pendulum animation.
Conservation of EnergyConservation of Energy
If energy is conserved, why do swings eventually slow to a stop? Mechanical Thermal
View rolling ball animations.
Your Body and EnergyYour Body and Energy
Everybody, raise both hands.In terms of energy, what happened?
PEKEEvery second, chemical PE (stored
when you eat) is converted into: Heat (constant body temperature
and given off to surroundings) Other daily functions (heart beat,
digesting, walking, etc.)
Your Body and EnergyYour Body and Energy
The food Calorie (C) is a unit used to measure how much energy you get from foods. 1 C = 4184 J 1 g of fat = 9 C 1 g of carbs or
protein = 4 C
Video and VLabVideo and VLab
http://www.brainpop.com/science/energy/formsofenergy/
http://www.brainpop.com/science/energy/kineticenergy/
http://glencoe.mcgraw-hill.com/sites/0078779626/student_view0/unit1/chapter4/virtual_lab.html
Self-Check 4Self-Check 4
1. 3 gram ball on a top shelf and a 3 gram ball on a bottom shelf. Which has more PE?
2. 2 gram ball and 6 gram ball move at 3 m/s. Which has more KE?
3. Friction converts ___________ energy into _________ energy.
top
6 gmechanical
thermal