1. Energy and Forces in Motion Unit 1 Physical Science HS Credit Mrs. Rubel

2. Work, by definition, is the product of the force exerted on an object and the distance the object moves in the direction of the force. W = F·d

3. What is Energy? Energy is the ability to do work. The Law of Conservation of Energy says: Energy cannot be created or destroyed, it can only change form. Change requires energy. Energy comes in many forms: Energy comes in many forms: mechanical, electrical, magnetic, solar, mechanical, electrical, magnetic, solar, thermal, chemical, etc... thermal, chemical, etc...

4. Nuclear Energy Nuclear Fusion occurs when the nuclei of 2 or more atoms fuse together Example: The Sun (2 hydrogen become helium) Nuclear Fission occurs when the nuclei of an atom is split apart (atomic bomb)

5. The SI unit of work is the Joule, named in honor of James Prescott Joule James Prescott Joule James Prescott Joule James Prescott Joule. One Joule, J, of work is the work done when 1.0 N of force is applied through a distance of 1.0 m.

6. Potential Energy Potential Energy is the energy an object has because of its position or shape. The object is ready to move, but not yet in motion. Examples: A stretched rubber band, a wind-up toy.

7. Potential Energy Due to Gravity Gravitational Potential Energy occurs when gravity is the force used to create the potential energy. The more force you build UP against gravity, the greater the GPE. Examples: the low dive vs. the high dive at a swimming pool. Throwing a penny off a chair vs. the Empire State Building!

8. GPE Equation What is the gpe of an object that has a mass of 9.0 kg and is 3.0 m above the ground? GPE = mgh ( g =acceleration of gravity = 9.8 m/s 2 ) GPE = (9.0)(9.8)(3.0) = 264.6 J J = Joules, the SI unit for work and energy

9. Potential Energy energy of position or condition elastic potential energy (like the stretched rubber band) (like the stretched rubber band) PE e = ½ kx 2 k – elastic constant in N/m k – elastic constant in N/m x - elongation or compression in m x - elongation or compression in m PE e – elastic potential energy in J PE e – elastic potential energy in J Click here to investigate elastic constants. here

10. Chemical Potential Energy Remember that a chemical change occurs when 2 or more different elements are combined to create a new substance. Chemical potential energy is greatest just before the actual chemical change. Example: The side of the marshmallow is completely brown just before it begins burning!

11. Kinetic Energy Kinetic energy is the energy of motion. All moving objects have kinetic energy. Kinetic energy depends on speed and mass. The faster the object is moving, the more kinetic energy. Kinetic energy increases as the mass of the object increases.

12. Kinetic Energy Equation A baseball with a mass of 3.0 kg is moving at a speed of 6.0 m/s. What is its kinetic energy? KE = ½ mv 2 KE = ½ (3.0)(36.0) = 54 J

13. From Potential to Kinetic An object’s greatest potential energy is just before it begins to move (ex: winding up a toy) Once the object begins moving, it has kinetic energy. The object has it’s greatest kinetic energy just before it begins to slow down or stop.

14. Conversions between Kinetic and Potential Energy Mechanical energy is the total amount of potential and kinetic energy in a system and can be expressed as Me = pe + ke

15. Potential vs Kinetic http://www.youtube.com/watch?v=Jnj8m c04r9E&safety_mode=true&persist_safety _mode=1&safe=active And the day he was caught…. https://www.youtube.com/watch?v=KJJW 7EF5aVk