Transcript The nature of Energy

Extra Credit
Poster presentation (full poster)
Pick a topic – projectile motion, newton’s
laws, or Work and Power
Must include:
Picture
Title
10 vocabulary words
3 higher level questions and answers
5 key points
Work cited
How will this extra credit help?
Replace a minor grade
Or
Up to 20 points added to a major grade
When is this due?
No later than Thursday the 5th at 5pm.
The Nature of
Energy
Energy
The ability to cause change or the
ability to do work
Unit for Energy – Joule (J)
Energy
 Two main types of energy:
Kinetic
Potential
 Other types of energy include…
 Thermal
 Light
 Sound
 Electrical
 Chemical
 Nuclear
Kinetic energy
Energy in the form of motion
Kinetic energy = ½ x mass x velocity2
KE =
2
½mv
Potential Energy
Energy stored in a motionless
object, giving it the potential to
cause change
3 Types of Potential Energy
 Elastic Potential Energy – Energy stored by
things that stretch or compress (springs,
elastic, rubberbands)
Chemical Potential Energy - energy
stored in chemical bonds between atoms
(Snickers bar, food, even gasoline)
Gravitational Potential Energy – energy
stored by things that are above Earth
(book sitting on shelf, person standing on
a cliff, rollercoaster perched at the top of a
hill)
Gravitational Potential Energy
PE = mass x acceleration due to gravity
x height
PE = mgh
Law of Conservation of Energy
Energy cannot be created or
destroyed, only change form.
MEi = MEf or…
KEi + PEi = KEf + PEf
Law of Conservation of Energy (example)
 Fuels store energy in the form of chemical
potential energy.
 This energy is transformed into heat energy,
which is then transformed into kinetic energy.
Ex: 1…gasoline put into your car (chem. Pot.
Energy)…it is heated/combusted and a chemical
reaction occurs so that the energy stored in the
bonds can be released in the form of heat.
Then, the heat energy is used to move parts like
pistons, etc (kinetic energy) …which eventually
moves your car!
Ex: 2…Candy bar has chemical potential
energy…you eat it…your body digests it,
meaning it breaks down the food – even
breaking the bonds and releasing energy.
Your body uses the energy to move
(kinetic energy)!
Example Problem 1
A 50 kg boy and his 100 kg father went
jogging. Both ran at a rate of 5 m/s. Who
had more kinetic energy? Show your work
and explain.
Example Problem - answer
KE = ½mv2
Boy…
KE = ½(50 kg)(5 m/s)2
KE = 625 J
Dad…
KE = ½(100 kg)(5 m/s)2
KE = 1250 J
had more Kinetic energy because his mass was
Dad
greater.
Example Problem 2
What is the potential energy of a 10 N
book that is placed on a shelf that is 2.5
meters high?
Example Problem 2 - answer
GPE = mgh
GPE = (10 N) (2.5m)
GPE = 25 J
Remember that weight = mg
and that the force provided is
weight.
NOTE: you may want to change
your variable for weight to Fg.