What is Energy?

1. What is Energy? Chapter 9 Section 1

2. Energy and Work: Working Together • The ability to do work or cause change is energy. • You can think of work as the transfer of energy. • Anytime a change occurs, energy is transferred from place to place. Ex: hearing footsteps, moving leaves • Both energy and work are expressed in joules(J). • Kinetic Energy • The two kinds of energy are kinetic energy and potential energy. • The energy of motion is kinetic energy. • Kinetic Energy Depends on Mass and Speed • The kinetic energy of an object depends on both its mass and its velocity (speed). Kinetic energy increases as mass and/or velocity increases. • Kinetic Energy = mass x velocity2 2

3. Math Focus p.241 • Kinetic Energy = mass x velocity2 2 Kinetic Energy = 2400 kg x (20 m/s)2 2 Kinetic Energy = 2400 kg x 400 m2/s2 2 Kinetic Energy = 960000 kg x m2/s2 2 Kinetic Energy = 480000 J or 480 kJ This car has twice the kinetic energy of the 1200kg car in the example.

4. Math Focus p.241 • Kinetic Energy = mass x velocity2 2 Kinetic Energy = 4000 kg x (2 m/s)24000 kg x (4 m/s)2 2 2 Kinetic Energy = 4000 kg x 4 m2/s24000 kg x 16 m2/s2 2 2 Kinetic Energy = 16000 kg x m2/s264000 kg x m2/s2 2 2 Kinetic Energy = 8000 J or 8 kJ 32000 J or 32 kJ The elephant has 4 times as much kinetic energy of the running only twice as fast.

5. Math Focus p.241 • Kinetic Energy = mass x velocity2 2 Kinetic Energy = 2000 kg x (30 m/s)2 2 Kinetic Energy = 2000 kg x 900 m2/s2 2 Kinetic Energy = 1,800,000 kg x m2/s2 2 Kinetic Energy = 900,000J or 900 kJ

6. Math Focus p.241 • Kinetic Energy = mass x velocity2 2 Kinetic Energy = 3000 kg x (20 m/s)2 2 Kinetic Energy = 3000 kg x 400 m2/s2 2 Kinetic Energy = 1,200,000 kg x m2/s2 2 Kinetic Energy = 600000 J or 600 kJ

7. Potential Energy (A,B,C together) • Energy that is stored is potential energy. • Ex: a wound spring, an object that has been lifted into the air or to the top of a hill • The potential energy associated with objects that can be stretched or compressed is called elastic potential energy. • Potential energy that depends on height is gravitational potential energy. • Gravitational potential energy is equal to the work done on an object to lift it. • Gravitational potential energy = weight x height • Unit of energy is the joule (J).

8. Math Focus p.242 • Gravitational Potential Energy = weight x height GPE = 40 N x .8 m GPE = 32 J • GPE = weight x height GPE = 500 N x 10 m GPE = 5000 J • GPE = weight x height GPE = 600 N x 8 m GPE = 4800 J

9. Mechanical Energy • Mechanical energy is the total energy associated with the motion and/or position of an object. • Mechanical energy = kinetic energy + potential energy • Mechanical Energy in a Juggler’s Pin • An object’s potential energy can change to kinetic and vice versa, but the mechanical energy of an object will not change (unless some energy is transferred to another object). • As an object is thrown up, its kinetic energy changes to potential until it reaches its highest point. As it starts to descend, the potential energy changes back into kinetic.

10. Other Forms of Energy • Some of the major forms of energy are mechanical, thermal, chemical, electrical, sound, electromagnetic (radiant), and nuclear energy. • Thermal Energy • Thermal energy is the total energy of the particles of a substance or material. • Chemical Energy • Chemical energy is the energy stored in chemical bonds that hold compounds together. • Electrical Energy • Moving electric charges produce electricity and the energy they carry is called electrical energy.

11. Sound Energy • The energy carried by waves of vibrating particles is sound energy. • Ex: speakers, a plucked guitar string • Electromagnetic (radiant or light) Energy • Energy that travels in waves (of electrically charged particles) is known as electromagnetic energy -- includes all waves in the EM spectrum. • Nuclear Energy • Nuclear energy is the energy stored in the nucleus of an atom and is released during nuclear reactions. • 2 types - fusion and fission