Download Unit: Energy

Unit: Energy
Sections: Transfer & Conservation of Energy
Potential & Kinetic Energy
Potential Energy
Kinetic Energy
Key Words: energy, energy transfer, law of conservation of energy, work, potential energy, kinetic energy,
gravity, chemical potential energy, thermal energy, heat, temperatureradiant energy, nuclear
energy, sound, mechanical energy, friction, force, acceleration
Essential Questions (by Section):
Transfer & Conservation of Energy
- What is the Law of Conservation of Energy and where does this law apply?
- How is energy transferred in a simple system?
- Why is energy conserved as it transfers between objects in a closed system?
Potential & Kinetic Energy
- What is potential energy?
- What is kinetic energy?
- How does the law of conservation of energy apply to kinetic and potential energy?
Potential Energy
- What is potential energy and what are some examples of it?
- What are two types of potential energy?
- What is the difference between potential energy and kinetic energy?
- How does potential energy turn into kinetic energy?
Kinetic Energy
- What is kinetic energy?
- What are some examples of kinetic energy?
- How does kinetic energy turn into potential energy?
Transfer & Conservation of Energy
Law of Conservation of Energy
- energy cannot be created or destroyed
- can change form or transfer from one object or place to another
- “closed system” no energy escapes
o Total amount of energy always remains the same
o Very few systems are “closed”
o Most “leak” thermal energy
o Energy is lost due to contact or friction
o Energy input is higher than output – difference is due to loss of thermal energy
o Circuit (system)
 Chemical energy (battery) converts to electrical energy (current) to radiant energy (light
bulb)
 Some chemical energy changes to thermal energy lost by the light bulb and wires (heat)
 Radiant energy (light bulb) + thermal energy lost (light bulb & wires) = chemical energy
(battery)
 Energy is transferred and some is lost but no amount changes (no energy is created or
destroyed)
Potential & Kinetic Energy
Energy – the ability to do work or cause change
- falls under two categories:
o Potential energy
 energy an object has due to its position or chemical composition
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energy that is “stored” until it can be converted to kinetic energy
includes:
gravitational
chemical
nuclear
elastic
electric
o Kinetic energy
 energy an object has due to its motion
 includes:
heat (vibrational, rotational, translational motion of atoms)
electrical (motion of electrons)
Sound (wave motion of oscillating particles of matter)
Any motion of objects
Even when “standing still” molecular movement is still vibrating
Absolute zero – where all molecular motion stops
Temperature – a measure of kinetic energy
o Directly proportional
o Higher temps = higher KE
Law of conservation of energy
o How it applies
 Energy is continually changing from kinetic to potential and potential to kinetic
 During conversions, energy is always “lost”
Never 100% efficient
Lost as “heat” (another form of energy)
Ex. Picking up a ball from the ground
o Some energy from your body is converted to GPE (gravitational potential
energy) in the ball
o Drop the ball, as it hits the ground, KE is converted to sound and heat
o Shape of ball has PE called “elastic PE” when ball deforms from impact
o Ball springs back into shape converts EPE to KE
o Ball does not go as high on next bounce because of energy lost as sound and
heat
Potential Energy
System
- all the parts of an energy system
o uses energy
 ability to do work
o uses “forces”
 a push or pull
- has both PE and KE
- PE depends upon position and condition
o Can be CPE (chemical)
 Energy stored in chemical bonds
 Changes to heat when an object burns
o Can be GPE (gravitational)
 Skier on top of a mountain
 Bow & arrow
Kinetic Energy
KE – object has due to motion
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KE = ½ mv2
o KE = one half * mass of the object * the object’s velocity squared
o Ball is 100g (mass), moving at 25 m/s – what is the KE?
 ½ (100g)(25)2
 ½ (100g)(625)
 ½ (62500)
 KE = 31,250 J (J = Joules = Kg*m/s –> units of energy)
Energy – ability to do work
o work is applying a force to move a mass over a distance
Law of conservation of energy
o KE is transferred from one object to another
o Ex. bat hits a ball -- > the KE of swinging the bat transfers to the ball
 Ball goes flying through the air
o Ex. skier going up a lift to the top of a mountain
 the lift provides the KE
 building GPE due to height of the mountain
GPE increases as any object increases altitude
other forms of KE
o electricity
 generators move water or steam by spinning turbines
 converts mechanical energy to electrical energy