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)

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

Kinetic Energy

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

KE= ½ mv2

Step 2: Rewrite your equationStep 3: Substitute your givens for all variables

possible

Step 1: write down all of your givens(any information the problem gives you)

Step 4: Solve the algebra problem

* Don’t forget your units!!!

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?

Bowling Ball Demo. Check Your Understanding

“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

Gravitational Potential Energy

Example: a 3kg rock sits at the top of a cliff 100 meters high, how much gravitational potential energy does the rock have?

mass=3kgg= 9.8height= 100mGPE=?

GPE=mghGPE=(3)(9.8)(100)GPE=2,940Joules

PE=mgh

Step 1: write down all of your givens(any information the problem gives you)

Step 2: Rewrite your equationStep 3: Substitute your givens for all variables

possibleStep 4: Solve the algebra problem

* Don’t forget your units!!!

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?

Bowling Ball Demo.Check Your Understanding

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)

Law of Conservation of Energy

The pendulum starts at position 1, swingsto position 5 and back to position 1. 1. At position 1 GPE=10Joules, how much KE is present

at position 1? 2. At position 2 the GPE has decreased to 5 Joules, how

much KE is present at position 2? 3. At position 3 GPE has dropped to is minimum of 0

Joules, how much KE is present? 4. At position 4 KE has dropped back to 5 Joules, how

much GPE is now present?5. At position 5, KE reaches is minimum as the pendulum

prepares to swing back, how much GPE is present?

TEbefore=TEafter