Chapter 9Energy and Energy Resources Section 1 What is Energy?
Energy and Work- Working together What is energy? Energy is the ability to do work What is work? Work occurs when a force causes an object to move in the direction of the force. (Work transfers energy)
Kinetic Energy is Energy of Motion • An object which has motion-whether it be vertical or horizontal motion- has kinetic energy (KE) • Three forms of KE are vibrational, rotational, and translational • To keep it simple, we will focus on translational KE or the energy due to motion from one location to another
Potential Energy Is Energy of Position • Potential energy is the energy an object has because of its position or shape.
Potential Energy Is Energy of Position • When in their resting position, they have no energy. The potential energy comes from the change in shape or position from it’s usual shape
Potential Energy Is Energy of Position • A rubber band is another good example of potential energy. No energy potential energy
Gravitational potential energy is the energy stored in an object as the result of its vertical position or height. • The gravitational potential energy of the massive ball of a demolition machine is dependent on two variables - the mass of the ball and the height to which it is raised.
There is a direct relation between gravitational potential energy and the mass of an object. • More massive objects have greater gravitational potential energy. • There is also a direct relation between gravitational potential energy and the height of an object. • The higher that an object is elevated, the greater the gravitational potential energy.
To determine the gravitational potential energy of an object, a zero height position must first be arbitrarily assigned. Typically, the ground is considered to be a position of zero height. In the lab, the desk could be zero height. Since the gravitational potential energy of an object is directly proportional to its height above the zero position, a doubling of the height will result in a doubling of the gravitational potential energy. A tripling of the height will result in a tripling of the gravitational potential energy.
Forms of Energy: Thermal Energy • All energy involves either motion or position • Thermal energy: all particles of matter are in constant motion so they have kinetic energy. Particles also have energy because of molecular arrangement • Thermal energy is the total energy of the particles that make up an object
Forms of Energy: Chemical Energy • Chemical energy is the energy of a compound that changes as its atoms are rearranged to form new compounds • Chemical energy is a form of potential energy • When compounds, like sugar in some foods are formed, work is done to bond the atoms to form molecules
Forms of Energy:Electrical Energy • Electrical Energy is the energy of moving electrons • When an electric appliance is plugged in to an outlet, the electrons in the wires move back and forth transferring energy and producing the work of the stereo which is to produce sound. • Electrical energy can be a form of potential energy
Forms of Energy:Sound Energy • Sound is created by the movement of air past the vocal cords making them vibrate • Sound energy is caused by an objects vibrations • Sound energy is a form of potential and kinetic energy
Forms of Energy:Light Energy • Light energy is produced by the vibrations of electrically charged particles
Forms of Energy:Nuclear Energy • Nuclear energy is formed by fusing nuclei or splitting them… fusion or fission
Energy and Machines • You transfer energy to the nutcracker and it transfers energy to the walnut • The nutcracker will not transfer more energy to the walnut than you transfer to the nutcracker
Energy and Machines • Machines are energy converters • When machines transfer energy, energy conversions can often result
Let’s summarize • What determines an objects thermal energy? An objects thermal energy depends on its temperature, the arrangement of its particles, and the number of particles in the object
Let’s summarize • Describe why chemical energy is a form of potential energy. When a substance forms, work is done to bond particles of matter together. The energy that creates the new bonds is stored in the substance as potential energy
Let’s summarize • When you hit a nail into a board using a hammer, the head of the nail gets warm. IN TERMS OF KINETIC AND POTENTIAL ENERGY, DESCRIBE WHY THIS HAPPENS. The kinetic energy of the moving hammer is transferred to the head of the nail, causing particle sin the nail to move faster. The faster the particles move, the greater their thermal energy.
EQ #1 Explain the relationship between energy and work • Energy is the ability to do work. Work cannot occur without energy
Let’s Review When you bounce a basketball, you give it kinetic energy. At the moment the ball hits the ground, its kinetic, its kinetic energy energy is greatest and its potential energy is zero. At that moment, the change in the shape that occurs when it hits the ground gives the ball potential energy that is used when the ball moves back upward. When the ball bounces back up toward your hand , its kinetic energy is converted into potential energy because the position changes. At the moment the ball is at the top of its bounce, its kinetic energy is zero.
Why energy conversions are important • They make energy useful by converting energy to a form of energy we can use • Energy efficiency is a comparison to the amount of energy before a conversion with the amount of useful energy after a conversion…efficiency means less waste • Work input is always greater than work output