Download Unit 4: Energy

Unit 4:
Energy
Kinetic &
Potential
Energy
Students will be able to (SWBAT)
• Describe
different
types of
potential
and kinetic
energy.
Date:


Energy is a quantity that measures the
ability to cause change in a physical
system.
Some things that have energy…
— Wind (moves things)
— You (move)
— Batteries (can make things move)
— Gasoline (burns to move a car)
— A ball at the top of a hill (moves)

The unit for
energy is the
joule (J).

1 calorie =
4187 J
• Energy an object has due to its
condition or position (stored energy).
• Example
– Snow blower filled with gasoline
– Car at the top of a hill
– Soccer ball on a table
– Spring that is compressed
– Stretched rubber band
• Energy an object has due to
motion.
• Examples
– Ball rolling off a table
– Throwing a ball
– Gas molecules bouncing around a room
– Skydiver jumping out of a plane
Where is the
energy
coming
from?
1.Gravitational Potential
Energy: energy stored in
an object because of where
it is placed. It is found in
object some height off the
ground.
Where is the
energy
coming
from?
2. Mechanical Potential
Energy: energy that is
stored by the forces within
tension, such as in a
rubber band or spring.
Where is the
energy
coming
from?
3.Chemical Potential Energy:
energy is stored in the
bonds between atoms and
molecules, such as in
photosynthesis.
Where is the
energy
coming
from?
4. Nuclear Energy : energy
stored in the nucleus of an atom.
Ex: used in Nuclear power plants
Bryon Power
Plant near NIU
Where is
the energy
coming
from?
1.Radiant Energy :
electromagnetic
energy that travels in
waves. Ex: x-rays,
sunlight
Where is
the energy
coming
from?
2. Thermal Energy: vibration
and movement of the atoms
and molecules within
substances. Ex: heat
Where is
the energy
coming
from?
3. Motion Energy: energy
stored in the movement of
objects. The faster they move,
the more energy is stored.
Where is
the energy
coming
from?
4.Sound Energy: movement of
energy in waves and
produced when a force causes
an object or substance to
vibrate.
Where is
the energy
coming
from?
5. Electrical Energy: delivered
by tiny charged particles called
electrons. EX: Lightning
Unit 4
Pre-test
Review
Students will be able to (SWBAT)
• Solve for kinetic
energy.
• Solve for potential
energy.
• Solve problems
using conservation
of energy.
Date:
Energy Formulas
Solve for Potential and Kinetic Energy
A 2-kg rock falls off a 20 m cliff. When
it is halfway down, it is traveling at 14
m/s.
Kinetic energy and potential energy at the
top: _______________
Potential Energy half way: ___________
Kinetic energy and potential energy at the
bottom: _________________
Potential and kinetic energy
Solution:

Kinetic energy at the top:
0J

Potential energy at the top:
Ep= (2 kg)(9.8 N/kg)(20 m) = 392 J

Potential energy halfway down:
Ep= (2 kg)(9.8 N/kg)(10 m) = 196 J

Kinetic energy at the bottom:
392 J

Potential energy at the bottom:
0J
• Energy cannot be created
or destroyed
• It can only be transformed
(changed) from one form
to another.
• The total amount of energy
in the universe never
changes.
Using and conserving energy
 When
you “use” energy by turning on a light, you
are really converting energy from one form
(electricity) to other forms (light and heat).
 In
the “physics” sense, the energy is not “used up”
but converted into other forms of energy.
 The
total amount of energy
stays constant.
Objective Review:
Solve kinetic and potential energy using
conservation of energy.
• What is the potential energy of a 2 kg potted
plant that is on a 1 m high plant stand?
Ep = mgh
2kg x 9.8m/s 2 x 1m = 19.6 J
• What is the kinetic energy of a 3 kg ball that is
rolling at 2 m/s?
Ek = ½ mv2
0.5 x 3kg x (2m/s)2 = 6 J