Conservation of Energy – Energy Conversion 15.2 – Energy Conservation Conservation of Energy – Energy Conversion

Learning Objectives Section 15.1 Describe conversion of energy from one form to another. State and apply the Law of Conservation of Energy. Analyze how energy is conserved in conversions between kinetic and potential energy and solve equation that equates initial energy to final energy. Describe the relationship between energy and mass and calculate how much energy is equivalent to given mass.

Can energy be converted from one form to another? Yes!!!!!!!!! The process of changing energy from one form to another is energy conversion. The striking of a match is a good example. Muscles use chemical energy to move the match. Friction between the match and the matchbox converts kinetic energy into thermal energy. Chemical energy is converted into thermal energy and electromagnetic energy in the flame.

What is the Law of Conservation of Energy? The law of conservation of energy states that energy cannot be created or destroyed. When energy changes from one form to another, the total energy remains unchanged, even though many energy conversions may occur. In a closed system, the amount of energy present at the beginning of a process is the same as the amount of energy at the end.

More on Conservation of Energy The work done by friction changes kinetic energy into thermal energy. Friction within machinery reduces efficiency. Friction is a major cause of energy consumption in cars and factories. In many cases, most of a falling object’s potential energy is converted into thermal energy because of air resistance.

What energy conversion takes place object falls towards Earth? The gravitational potential energy of an object is converted to the kinetic energy of motion as the object falls. One of the most common energy conversions is between potential energy and kinetic energy. An avalanche brings tons of snow from the top of a mountain to the valley floor. The elastic potential energy of a compressed spring is converted into kinetic energy as the spring expands. Energy conversions can go from kinetic to potential energy or from potential to kinetic energy

The Energy Conversion In Pendulums A pendulum consists of a weight swinging back and forth from a rope or string. At the highest point in its swing, the pendulum has zero kinetic energy and maximum potential energy. As the pendulum swings downward, potential energy is converted to kinetic energy. At the bottom of the swing, the pendulum has maximum kinetic energy and zero potential energy. .

Energy Conversion and the Pole Vault In the pole vault, an athlete uses a flexible pole to propel himself over a high bar. Some of the pole-vaulter’s kinetic energy is converted into elastic potential energy as the pole bends. The pole springs back into shape, propelling the pole-vaulter upward. As the pole-vaulter rises, his kinetic energy decreases while he gains gravitational potential energy. Once the highest point has been reached, his gravitational potential energy begins to convert back to kinetic energy.

Energy Conversion Calculations When friction is small enough to be ignored, and no mechanical energy is added to a system, then the system’s mechanical energy does not change. Mechanical energy = KE + PE The law of conservation of energy applies to any mechanical process. If friction can be neglected, the total mechanical energy remains constant.

Practice Problem Conservation of Energy At a construction site, a 1.50-kg brick is dropped from rest and hits the ground at a speed of 26.0 m/s. Assuming air resistance can be ignored, calculate the gravitational potential energy of the brick before it was dropped.

How are energy and mass related? Einstein’s equation, E = mc2, says that energy and mass are equivalent and can be converted into each other. Albert Einstein developed his special theory of relativity in 1905. This theory included the now-famous equation E = mc2. E is energy, m is mass, and c is the speed of light. The speed of light is an extremely large number, 3.0 × 108 meters per second. A tiny amount of matter can produce an enormous amount of energy. .

Example of Energy and Mass Suppose 1 gram of matter were entirely converted into energy. E = mc2 = (10–3 kg) × (3 × 108 m/s) × (3 × 108 m/s) = 9 × 1013 kg•m2/s2 = 9 × 1013 J 1 gram of TNT produces only 2931 joules of energy.

More on Energy and Mass In nuclear fission and fusion reactions, however, large amounts of energy are released by the destruction of very small amounts of matter. The law of conservation of energy has been modified to say that mass and energy together are always conserved.