Energy

What is Energy? Energy is the ability to do work. Work occurs when a force causes an object to move in the direction of the force. When work is done, energy is given by one object to another. Work and energy are expressed in the unit joules (J). Remember…1 joule = 1 Newton-meter

Kinetic Energy Kinetic Energy is the energy of motion. K.E.= mv2/2 m= mass v=velocity Velocity- the speed of an object in a particular direction Speed has a greater impact on Kinetic Energy than mass because it is squared.

Potential Energy Potential Energy- the energy an object has because of its position or shape. Examples: a diver on top of a platform a stretched bow books on a bookshelf The objects are not moving but have ‘stored’ energy because work has been done to move it into position It has “potential” to move!

Gravitational Potential Energy The diver on the platform has a specific kind of potential energy known as gravitational potential energy…gravity opposes the work done to keep the diver on the platform. G.P.E=weight x height Example: a 25N object (2500g) at a height of 3m has a potential energy of what? Don’t forget units! 75J

Try These! What is the kinetic energy of a 4,000 kg elephant running at 3 m/s? If you lift a 50 N watermelon to the top of a 2 m refrigerator, how much gravitational potential energy do you give the watermelon?

Mechanical Energy The total energy of motion and position of an object Mechanical Energy = potential energy + kinetic energy (M.E =P.E.+K.E.) Since the Law of Conservation of Energy tells us that energy cannot be created or destroyed, only transferred, we can assume that M.E. remains constant. Therefore, as potential energy increases, kinetic energy decreases and vice versa.

Forms of Energy: Thermal Energy Chemical Energy Electrical Energy Sound Energy Light Energy Nuclear Energy

Thermal Energy The total energy of the particles that make up an object. At higher temperatures, particles move faster. The faster the particles move, the more kinetic energy they have and the greater the object’s thermal energy is. Particles of a substance that are farther apart have more energy than particles of the same substance that are closer together.

Chemical Energy The energy of a compound that changes as its atoms are rearranged to form new compounds. Chemical energy is a form of POTENTIAL ENERGY

Electrical Energy Energy of moving electrons. Electrical energy available to your home is produced at power plants. Huge generators rotate magnets within coils of wire to produce electrical energy. Is a form of potential energy

Sound Energy Caused by an objects vibrations. Form of potential and kinetic energy

Light Energy Produced by the vibrations of electrically charged particles. Cause energy to be transmitted

Nuclear Energy Energy associated with changes in the nucleus of an atom. Formed when 2 things happen: 2 or more nuclei join together Nucleus of an atom splits apart

Energy Conversions Energy conversion: a change from one form of energy into another. Any form of energy can be converted into any other form of energy, and often one form of energy is converted into more than one other form.

From Kinetic to Potential and back Example: Jumping on a trampoline- You are in motion when you jump…K.E. Each time you jump, you change your position with respect to the ground, which is potential energy. The trampoline also stretches when you jump on it which is potential energy. Using a pendulum as an example, explain the P.E. and K.E.

Conversions involving Chemical Energy List the energy conversions during the process of photosynthesis… What do you start with? What does it go to?

Conversions Involving Electrical Energy Example: Hair Dryer Electrical Energy enters through the cord and is converted into kinetic energy as a small electric motor spins a fan blade. Electrical Energy is also converted into thermal energy as a grid of wires heats up.

The Law of Conservation of Energy This Law applies to a ‘closed system’ The Law of Conservation of Energy states that energy cannot be created or destroyed, only transferred (converted). Explain the Law of Conservation of Energy using a roller coaster as an example. Keep in mind that friction (oppositional force) converts kinetic energy into thermal energy and sound energy.

No conversions without Thermal Energy Any time one form of energy is converted into another form, some energy is converted into thermal energy (heat). This simply means that heat is either taken in, or given off.