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.

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.

Lesson Opener

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

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!

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

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

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

Unit 8, Lesson 2 – Mechanical Energy

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

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)

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

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!

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!!!!

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

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

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.

Visual Summary

Exit Question Why doesn’t a pendulum swing forever?