Energy Section 14.3 Energy

Potential and Kinetic Energy

Energy All Energy Potential Energy Kinetic Energy Gravitational Elastic Chemical

Energy The basic motion of energy is stored work. A tankful of gas, a heavy truck moving at speed, and a charged automobile battery all possess energy. The energy associated with a mass in motion is called kinetic energy The energy that is stored is called potential energy.

Potential Energy Potential Energy Energy that is stored and waiting to be used later

Gravitational Potential Energy Potential energy due to an object’s position above the surface. Formula PE = m∙g·h m = mass (kg) g = acceleration of gravity (9.8 m/s2) h = vertical component of displacement height (meters) (Note: m∙g = Newtons) Units: Joules (J)

Gravitational Potential Energy Example 1: A crate of mass 5,000 kg is raised slowly to a height of 12 m above its original position. What is the potential energy at the height of 12m? PE = m∙g·h PE = 5000 kg x 9.8 x 12 m PE = 588,000 J

Gravitational Potential Energy Thinker Question A baby carriage weighs 12 N. What is the potential energy if the carriage is sitting on a hill 21 m high? PE = m∙g·h (Remember m∙9.8 = Newton’s) PE = 12 N x 21 m PE = 252 J

Elastic Potential Energy Potential energy due to compression or expansion of a spring or an elastic object. Bow and Arrow Springs Stretched Rubber band

Chemical Potential Energy Potential energy stored within the chemical bonds of an object

Kinetic Energy Energy an object due to its motion Kinetic energy exists whenever an object which has mass is in motion with some velocity. The greater the mass or velocity of a moving object, the more kinetic energy it has.

Kinetic Energy Kinetic Energy Formula: KE = ½ mv2 m = mass (kg) V = Velocity (m/s) Units: Joules (J)

Kinetic Energy Example #2: What is the Kinetic Energy of a 1,000 kg car moving at 30 m/s? KE = ½ mv2 KE = ½ (1,000 kg) (30 m/s)2 KE = 450,000 J

Kinetic Energy Example #3: What is the Kinetic Energy of a 20,000 kg freight car moving at 25 m/s? KE = ½ mv2 KE = ½ (20,000 kg) (25 m/s)2 KE = 6,250,000 J

Kinetic Energy Example #4: What is the Kinetic Energy of a 0.00004 kg BB traveling 200 m/s? KE = ½ mv2 KE = ½ (.00004 kg) (200 m/s)2 KE = 0.8 J

Kinetic Energy Example #5: A pitcher throws a 0.145 kg baseball at a velocity of 30 m/s. How much kinetic energy does the ball have? KE = ½ mv2 KE = ½ (0.145 kg)(30 m/s)2 KE = 65.25 J