1. Unit 7: Energy. Bell Ringer.
What is the Law of Conservation of mass? Give an example
What are four signs of a chemical change?

2. Mass is neither created nor destroyed in a chemical reaction.
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.

3. Unit 7: Energy. Energy: the ability to do work
When an object does work on another, energy is transferred

4. Units for energy are Joules!
Unit 7: Energy.
Units for energy are Joules!

5. Unit 7: Energy. Two types of energy….
Kinetic Energy (KE): energy of motion
Potential Energy (PE): of position or shape

6. K𝑖𝑛𝑒𝑡𝑖𝑐 𝐸𝑛𝑒𝑟𝑔𝑦= 𝑚𝑎𝑠𝑠 × 𝑠𝑝𝑒𝑒𝑑 2 2
Unit 7: Energy.
K𝑖𝑛𝑒𝑡𝑖𝑐 𝐸𝑛𝑒𝑟𝑔𝑦= 𝑚𝑎𝑠𝑠 × 𝑠𝑝𝑒𝑒𝑑 2 2
K𝐸= 𝑚 𝑣 2 2

7. Let’s Try: What is the KE of the
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

8. Let’s Try: What is the KE of the
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!

9. Unit 7: Energy. 𝑃𝑜𝑡𝑒𝑛𝑡𝑖𝑎𝑙 𝐸𝑛𝑒𝑟𝑔𝑦=𝑤𝑒𝑖𝑔ℎ𝑡 ×ℎ𝑒𝑖𝑔ℎ𝑡 𝑃𝐸 =𝑤ℎ
Sometimes PE is referred to as “Gravitational Potential Energy!”
Same Thing

10. Unit 7: Energy. Height and weight affect PE
Circle who has greater PE for each

11. 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?

12. Unit 7: Energy. Putting it all together
Where does the pendulum have the greatest PE?
Where does the pendulum have the greatest KE?

13. ME can be all PE, all KE, or some of both!
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!

14. Unit 7: Energy.
𝑀𝐸=𝑃𝐸+𝐾𝐸

15. 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!