Download Section 3 What is energy? Energy “Ability to do work” Anything that

Section 3
What is energy?
Energy
 “Ability to do work”
 Anything that causes change must have energy.
 SI unit for all energies
 Joules (J)
Potential Energy
 Even motionless objects can have energy
 Stored energy due to position, shape, or condition
 Energy of Position
Elastic PE
 Energy stored by something that can stretch or compress
 Ex: rubber band, spring, bungee cord
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Gravitational PE
Energy stored by objects due to their position above Earth’s surface
Anything that can fall has stored energy
Increased by increasing its height
If two objects = height, larger mass more GPE
GPE
 GPE (J) =mass (kg) x gravity (m/s2) x height (m)
 GPE =mgh
• Gravity=9.8 m/s2
Mechanical energy
 ME= PE + KE
 Chemical PE
 Formation and breaking of bonds
 Match releases energy as light and heat
Kinetic energy
 The energy of an object due to its motion
 Depends on
 mass and speed
 Equation
 KE(J)=1/2 x mass(kg)x speed2(m/s)2
 KE=1/2mv2
Radiant energy
 Energy from the Sun
 warms the planet
 provides energy to plants
 Perform photosynthesis
Nuclear
 Fusion (sun)
 Atomic nuclei combine to form heavier nucleus
 Fission
 Single larger nucleus splits into 2 or more smaller nuclei
 Lightning
 Electrons moving through the air between the ground and a cloud
 Electrical energy
Energy in Plants
 Calorie
 Food energy
 1C=4,186 J
 Biofuel
 Ethanol and methane
Conservation of energy
Section 4
Roller coasters
 Propelling
 GPE, KE, heat
 Locations of KE/GPE
 Lowest PE/Highest KE: bottom of lowest hill
 Highest PE/Lowest KE: top of highest hill
Energy
 Law of conservation of energy
 Energy cannot be created nor destroyed
 A.k.a. 1st law of thermodynamics
 Lost energy
 Energy is lost as heat, sound, or vibrations
Types of systems
 Closed
 Energy but not matter exchanged
 Open
 Energy and matter are exchanged with the surroundings
 Isolated
 Neither energy nor matter are exchanged
Efficiency
 How much useful work a machine can do
 Equation
 Efficiency=useful work output/work input
 Unit %
 Why not 100% efficiency
 Every machine has some friction