1. Learning Objectives
I can describe a potential energy (PE) to kinetic energy (KE) transfer and KE to PE transformation in relation to mechanical energy.
I can explain the transformation of PE into KE in a functional pendulum system.
I can identify what forms of energy are transferred when work takes place.
I can explain how energy is different than work.

2. Ohio New Learning Standards for Science
Ohio 7th Grade, Physical Science #2 (7.PS.2) – Energy can be transformed or transferred but is never lost.
Ohio 7th Grade, Physical Science #3 (7.PS.3) – Energy can be transferred through a variety of ways.
Ohio 7th Grade, Science Inquiry & Application #3 (7.SIA.3) – Use appropriate mathematics, tools and techniques to gather data and information.

3. Lesson Opener

4. Unit 8, Lesson 2 – Mechanical Energy
What is mechanical energy?
- an object has mechanical energy if it is moving, if it is positioned above Earth’s surface, or both!
- kinetic energy is the energy of an object due to the object’s motion
- potential energy is the energy that an object has because of its position, shape, or chemical composition

5. Unit 8, Lesson 2 – Mechanical Energy
- objects interact with one another and can influence the types of energy other objects have
- the bow & bowstring have elastic potential energy (PE) because their shape changes
- the potential energy of the string transforms to the kinetic energy (KE) of the moving arrow
- the bowstring transfers mechanical energy to the arrow when it is released!

6. Unit 8, Lesson 2 – Mechanical Energy
- the total energy an object has because of its motion, change of position, or its shape is its mechanical energy
- mechanical energy is the sum of an object’s kinetic & potential energy

7. Unit 8, Lesson 2 – Mechanical Energy
How is energy conserved when mechanical energy transforms?
- an energy transformation occurs when energy changes from one form to another in a closed system
- pendulums stop moving because their energy transformations are not always 100% efficient!
- energy leaves the system through air resistance adding energy to the air molecules around it

8. Unit 8, Lesson 2 – Mechanical Energy
Newton’s Cradle
Complete #6, #7, #8, pg.551

9. Unit 8, Lesson 2 – Mechanical Energy

10. Unit 8, Lesson 2 – Mechanical Energy
When is mechanical energy transferred?
- mechanical energy is transferred when a force acts between objects and one of the objects moves some distance either with or against the force
- a force is a push or a pull exerted on an object in order to change the motion of the object
- forces have size, direction, and they transfer energy

11. Unit 8, Lesson 2 – Mechanical Energy
How are force and energy related to work?
- work is the use of force to move an object some distance and is measured by the following equation:
Work = Force x Distance
- force is measured in Newtons (N) & distance is measured in meters (m)

12. Unit 8, Lesson 1 – Mechanical Energy
- when you multiply Newtons by meters, the product is the joule
- therefore, work is measured in joules & mechanical energy is transferred when work is carried out!
- however, work can only be accomplished if the force is able to move the object in the direction of the force

13. Unit 8, Lesson 1 – Mechanical Energy
Test Yourself: What type of energy did the woman transfer to the apple by lifting it off the table & was work carried out?
Answer: mechanical energy & yes!

14. Unit 8, Lesson 2 – Mechanical Energy
How is energy different from work?
- energy is the ability to do work & work is a measure of how much energy a force transfers when it acts on a moving object
- work is NOT accomplished if the force is unable to move the object in the direction of the force because no mechanical energy has been transferred!!!!

15. Unit 8, Lesson 2 – Mechanical Energy
- if the men below carried the boxes, instead of pushing/pulling, work would not be done on the boxes
- carrying them would not place a force on the boxes because the upward lifting force is not in the same direction of the forward movement

16. Unit 8, Lesson 2 – Mechanical Energy
Complete #11 on page 553 and identify how much energy Trudy transfers to the puppy.

17. Unit 8, Lesson 2 – Mechanical Energy
distance = 1.2m; force = 44N
The amount of energy transferred (the work done).
work = force X distance
work = 44N X 1.2m
work = 52.8 J
N X m = J (Joules is the unit for energy & also for work.)
Trudy transfers 52.8 J of energy to the puppy.

18. Visual Summary

19. Exit Question
Why doesn’t a pendulum swing forever?