Bellwork– Take out a sheet of paper and work on this!!! What is the law of conservation of energy?

Video: https://www.youtube.com/watch?v=FX7T-QYTPho&t=17s

Energy Transfers and Transformations 6.2 Textbook pages 256-269

Law of conservation of Energy Energy can be transformed from one form to another but it cannot be created nor destroyed. Think about turning on a flash light. Within the flashlight you have a battery, an on/off switch, a bulb and a contact strip (usually copper or brass– carries current from the battery. Chemical potential energy is stored in the batteries, that chemical potential energy is transformed into electric energy. Electric energy moves through the contact strip to the bulb, that electric energy is transformed into radiant energy and thermal energy which shines out of the bulb. The amount of radiant energy that shines out of the flashlight cannot be more than the potential chemical energy that is stored in the batteries.

Law of conservation of Energy The amount of radiant energy given off by the flash light is less than the chemical potential energy stored in the batteries. In every energy transformation some energy transfers to the environment. When energy moves from one object to another without change of form it is considered an Energy Transfer. When one form of energy is converted to another form of energy it is considered an Energy Transformation. Think about swinging a tennis racket..When the mechanical energy of the racket changes the movement of the ball there is a transfer of energy (the balls mechanical energy increases as it is being hit!) NOW– think about where the mechanical energy from the racket comes from..

Laws of Conservation of Energy The chemical energy stored in your arm muscles (or the tennis players) transforms into mechanical energy in order to swing the racket. Identify an energy transfer and an energy transformation that occurs when someone plays the guitar. In the tennis racket example, why does the mechanical energy of the ball increase when it is hit?

Energy and Work The transfer of energy that occurs when a force makes an object move in the direction of the force is what we consider work. Work is only being done while the force is acting on the object. Think of the tennis player again, if they are standing still before the serve and using their muscles to hold the ball, they are not necessarily doing work on the ball. WHY? Because the ball is not moooooving. Once the tennis player hits the ball there is a force acting upon it, the ball is traveling a certain distance and we can calculate the work. Work is measured in Joules (J)

How to calculate work—you need to know how to calculate work! Use the formula W=Fxd W=Work F=Force applied to the object d= distance the force moved the object EXAMPLE: Student slides a book across a table and pushed that book with a Force of 8.5 newtons (N) and it travels a distance of 0.3m W=Fxd W=8.5x0.3 W=2.55  round up 2.6 J

Calculate Work—Practice A student lifts a backpack straight up with a force of 53.5 N for a distance of 0.6 m how much work is done on the backpack? A child pushes a toy truck 2.5m across the floor with a constant force of 22 N. How much work does the child do on the toy truck? These practice problems can be found on PG 260 of your text book.

Energy transformations and inefficiency Sometimes while energy is being transferred or transformed it is not completely efficient and all the energy doesn’t go where it is intended to go. Tennis racket example, your mechanical energy is being transferred to the ball but not ALL of it.. sometimes your hear that ball hit the racket (sound energy) some of that energy is also transformed to thermal energy.. Remember: Any time energy is transformed or transferred some energy ends up turning into thermal energy.. Think about the flashlight again.. Chemical energy from batteries is transformed into radiant energy and (wow you guessed it thermal energy)— some flashlights become warm to the touch. Even when the electric energy is moving through the circuit to become the radiant energy some of it is transforming into thermal energy.

Energy transformations and inefficiency Recall the law of conservation of energy Energy cannot be created nor destroyed When scientist say that energy transformations are inefficient, they DO NOT mean that energy is destroyed.. Energy transformations are inefficient because not all the energy being transformed ends up as energy that is usable! How is work the transfer of energy?

Open and Closed Systems Think of a car, it is a system.. Chemical potential energy (fuel) is transformed into mechanical energy (how it moves). Since we know that energy transformations are inefficient some of that chemical potential energy transforms into thermal energy and sound energy. (we can feel the warmth of the engine and hear the sounds of a running car, these are types of energy being released into the environment). An open system, such as a car engine is a system that exchanges matter or energy with the environment. A closed system is a system in which there are no matter or energy exchanges with the environment. In reality there are no closed systems because every physical system transfers some energy to its environment.

Renewable Energy Resources 264-266 A renewable energy resource is one that is replaced as fast or faster than it is used. Solar Wind Hydroelectric Geothermal Biomass

Non-renewable energy resources 268 Energy resources that are available is limited amounts or that are used faster than they are replaced in nature. Nuclear Energy- Comes from uranium which is only available in limited quanities Fossil Fuels- These are typically used faster than they can be replaced. Petroleum, natural gas, propane and coal are examples of fossil fuels.