Forms of energy (a) Radiant energy (b) Thermal energy 1. Radiant — energy in light, microwaves, and radio waves 2. Thermal — results from atomic and molecular motion – Temperature of an object is a measure of the thermal energy content 3. Chemical — results from the particular arrangement of atoms in a chemical compound; heat and light produced in this reaction due to energy released during the breaking and reforming of chemical bonds 4. Nuclear — released when particles in the nucleus of the atoms are rearranged 5. Electrical — due to the flow of electrically charged particles (c) Chemical energy (d) Nuclear energy (e) Electrical energy Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

Potential energy kinetic energy kinetic energy Energy in Energy out The energy something possesses due to its motion, depending on mass and velocity.

Energy KE = ½ m v 2 Kinetic Energy – energy of motion A C B Kinetic Energy – energy of motion KE = ½ m v 2 mass velocity (speed) Potential energy – Energy stored in an object because of the relative positions or orientations of its components Kinetic energy – Energy due to the motion of an object Kinetic energy, KE, of an object is related to its mass, m, and velocity v: KE = ½ mv2 Potential energy is equivalent to work: PE = Fd = mad = mgh m = mass, g = gravity (9.81 m/s2) and h = height Potential Energy – stored energy Batteries (chemical potential energy) Spring in a watch (mechanical potential energy) Water trapped above a dam (gravitational potential energy)

School Bus or Bullet? Which has more kinetic energy; a slow moving school bus or a fast moving bullet? Recall: KE = ½ m v 2 BUS BULLET KE = ½ m v 2 KE = ½ m v 2 Work – One definition of energy is the capacity to do work. – Easiest form of work to visualize is mechanical work, which is the energy required to move an object a distance d when opposed by a force F: work = force  distance or w = Fd – Because F, the force that opposes the action, is equal to the mass of the object times its acceleration, the preceding equation becomes work = mass  acceleration  distance or w = mad. KE(bus) = ½ (10,000 lbs) (0.5 mph)2 KE(bullet) = ½ (0.002 lbs) (240 mph)2 Either may have more KE, it depends on the mass of the bus and the velocity of the bullet. Which is a more important factor: mass or velocity? Why? (Velocity)2

Kinetic Energy and Reaction Rate lower temperature higher temperature minimum energy for reaction Fractions of particles Kinetic energy

Kinetic Energy and Reaction Rate lower temperature higher temperature minimum energy for reaction Fractions of particles Kinetic energy

Hot vs. Cold Tea Low temperature (iced tea) Many molecules have an intermediate kinetic energy High temperature (hot tea) Few molecules have a very high kinetic energy Percent of molecules Kinetic energy