Download Law of Conservation of Energy

Law of Conservation of Energy
Bowling Ball Demonstration
*Google Physics Bowling Ball Demonstration and watch a video that shows this
demonstration (Contact Ms. K. if you aren’t sure you have the right one)
Kinetic Energy
 Energy due to an objects motion
 KE= ½mv2
 Kinetic Energy = ½ (mass) X (velocity)2
 Velocity is the ONLY number that is squared
 Energy is measured in Joules
KE= ½ mv2
Example: If mass of an object is 10kg and velocity is 5 m/s, what is the
kinetic energy of the object?
 Mass= 10kg
 Velocity= 5m/s
 KE= ?
KE= ½ mv2
KE = ½ (10)(5)2
KE= 125 Joules
Step 1: write down all of your givens
(any information the problem gives you)
Step 2: Rewrite your equation
Step 3: Substitute your givens for all variables possible
Step 4: Solve the algebra problem
* Don’t forget your units!!!
Bowling Ball Demo.
Check Your Understanding
1. Where during the demonstration did you see kinetic energy?
2. Where do you think kinetic energy was greatest?
3. If the mass of the bowling ball is 5kg and the highest velocity it
reached was 20m/s, what is the greatest Kinetic Energy the
bowling ball reached?
Gravitational Potential Energy
 “Stored” energy due to an object’s position
 GPE= mgh
 Gravitational Potential Energy= (mass)X(9.8)X(height)
 g is always 9.8
 Again, energy is measured in Joules
PE=mgh
Example: a 3kg rock sits at the top of a cliff 100 meters high, how
much gravitational potential energy does the rock have?
mass=3kg
g= 9.8
height= 100m
GPE=?
Step 1: write down all of your givens
(any information the problem gives you)
GPE=mgh
Step 2: Rewrite your equation
Step 3: Substitute your givens for all variables possible
GPE=(3)(9.8)(100)
Step 4: Solve the algebra problem
GPE=2,940Joules
* Don’t forget your units!!!
Bowling Ball Demo.
Check Your Understanding
1. During the bowling ball demonstration, where did the ball
have gravitational potential energy?
2. During the bowling ball demonstration, where was
gravitational potential energy greatest?
3. When the bowling ball had the greatest gravitational potential
energy, did it have any kinetic energy?
4. If the height of an object was 2m and the mass was 0.5kg,
what is the gravitational potential energy of the object?
Law of Conservation of Energy
Energy is neither created nor destroyed, it is
transferred from one type to another
Total Energy= Kinetic Energy + Gravitational Potential Energy
TE= KE + GPE
The total energy in the system before an event equals the
total energy after an event. (TE stays the same in the
isolated system)
TEbefore=TEafter
The pendulum starts at position 1, swings
to position 5 and back to position 1.
1. At position 1 GPE=10Joules, how much KE is present
at position 1?
1. At position 2 the GPE has decreased to 5 Joules, how much KE is
present at position 2?
2. At position 3 GPE has dropped to is minimum of 0 Joules, how
much KE is present?
3. At position 4 KE has dropped back to 5 Joules, how much GPE is
now present?
4. At position 5, KE reaches is minimum as the pendulum prepares
to swing back, how much GPE is present?