Transcript Thursday, February 16th

Thursday, February 16th
Mechanical Energy
Today’s Goals
• Goal 1: SWBAT use the Law of Conservation of
Energy to explain why a situation in which
mechanical energy is lost cannot be possible.
• Goal 2: SWBAT determine points of high KE or
PE and low KE or PE in real-life situations.
• Law of Conservation of Energy
– energy cannot be created or
destroyed; total amount of
energy in the universe does
not change
• What else have you learned is
always conserved?
What Else is Conserved?
• Momentum
• Mass
Law of Conservation Example
Car Vibrates =
Kinetic Energy
Chemical Energy in Gasoline
Car heats up =
heat energy
Your Heater or AC =
energy not going to
moving forward
Mechanical Energy
• Mechanical Energy – total amount of
potential and kinetic energy in a system
• So, ME = Kinetic E + Potential E
• Remember there are 3 different types of
Potential Energy!
• So, Mechanical E depends on the motion of an
object (kinetic) and the position of the object
(potential)
Golf Swing Example
Sling Shot Example
Bungee Jump Example
Question 1
• Which of the following examples has
kinetic energy converting into
potential energy?
• A) A boulder rolls down a hill
• B) A ball is thrown upward
• C) A swing comes to a stop
• D) A bowling ball rolls horizontally
B!
Question 2
• The Gravitational Potential Energy of
an object changes when which of the
following changes?
• A) The object’s speed
• B) The object’s mass
• C) The object’s temperature
• D) The object’s length
B! (GPE = mgh)
Question 3
• The Kinetic energy of an object changes when
which of the following changes?
• A) The object’s chemical potential energy
• B) The object’s volume
• C) The object’s direction of motion
• D) The object’s velocity
D! (KE = ½
2
mv )
Question 4
• When an energy transformation occurs, which
of the following is true?
• A) Mechanical energy doesn’t change.
• B) Mechanical energy is lost.
• C) The total energy doesn’t change.
• D) Mass is converted into energy.
C!
As a group:
• Turn to page 150 in your text books.
• Complete questions #1-9 on separate piece
of paper. EACH PERSON NEEDS OWN PAPER
• Things that will HELP YOU:
–Gravity = 9.8 m/s/s
–K E = ½ mv2
–GPE = mgh (and m = PE/gh)
–For #8: The baseball’s velocity slows as it
goes UP, and speeds up as it goes DOWN