Transcript Kinetic vs. Potential Energy

Unit 7: Energy. Bell Ringer.
What is the Law of Conservation of
mass? Give an example
What are four signs of a chemical
change?
Unit 7: Describing Matter.
Law of Conservation of Mass.
Law of Conservation of Mass
Mass is neither created nor destroyed in a
chemical reaction.
Example: Burning a piece of paper.
It seems that the mass shrinks as the paper
burns.
Unit 7: Energy.
Energy: the ability to do work
When an object does work on another, energy is transferred
Unit 7: Energy.
Units for energy are Joules!
Unit 7: Energy.
Two types of energy….
- Kinetic Energy (KE): energy of motion
- Potential Energy (PE): of position or shape
Unit 7: Energy.
𝑚𝑎𝑠𝑠 × 𝑠𝑝𝑒𝑒𝑑 2
K𝑖𝑛𝑒𝑡𝑖𝑐 𝐸𝑛𝑒𝑟𝑔𝑦 =
2
𝑚𝑣 2
K𝐸 =
2
Unit 7: Energy.
Let’s Try: What is the KE of the
2,000 kg red car?
What is the KE of the
2,000 kg green car?
The red car has more KE than the green car because the red car is moving faster
Unit 7: Energy.
Let’s Try: What is the KE of the
10,000 kg truck?
The truck has more KE than the red car because the truck is more massive!
Unit 7: Energy.
𝑃𝑜𝑡𝑒𝑛𝑡𝑖𝑎𝑙 𝐸𝑛𝑒𝑟𝑔𝑦 = 𝑤𝑒𝑖𝑔ℎ𝑡 × ℎ𝑒𝑖𝑔ℎ𝑡
𝑃𝐸 = 𝑤ℎ
Sometimes PE is referred to as
“Gravitational Potential Energy!”
Same Thing
Unit 7: Energy.
Height and weight affect PE
Circle who has
greater PE for each
Unit 7: Energy.
Let’s Try: If you lift a 50 N watermelon to the top
of a 2 m refrigerator, how much PE do you give
the watermelon?
Unit 7: Energy.
Putting it all together
Where
does the
pendulum
have the
greatest
PE?
Where
does the
pendulum
have the
greatest
KE?
Unit 7: Energy.
Mechanical Energy (ME): the total energy
of motion and position of an object.
ME can be all PE, all KE, or some of both!
Unit 7: Energy.
𝑀𝐸 = 𝑃𝐸 + 𝐾𝐸
Unit 7: Energy.
Bell Ringer: You are on a roller coaster 92
meters above the ground traveling at 14 m/s.
You weigh 400 N (or approximately 40.8 kg).
What is your mechanical energy? Show your
work and include your units!