Energy Transfer and Electrical Circuits Week 4 Vocabulary

1. Electricity Brain pop The presence or movement of electrons which are tiny, negatively charged particles in an atom. An electrical force is the pushing and pulling of moving electrons

2. Current In order for electricity to be useful in our homes and devices, there needs to be a steady flow of electrons called a current.

3. Circuit The complete loop through which an electrical current can pass.

4. A Complete Circuit In a complete circuit, energy starts at a power source (for example a battery), moves through a conductor (for example, a metal wire), passes through a load (a device that uses electricity such as a light bulb or toaster) and returns back to the power source.

5. Batteries and Circuits Batteries use “energy transformation” to produce electricity. They work by changing stored chemical energy into electrical energy. A chemical reaction inside a battery creates electrons. These electrons are stored in the negative terminal (-) of the battery. When a battery is part of a complete circuit, the negative terminal pushes the electrons out. The electrons travel from the negative terminal, through the circuit to the positive terminal (+). The positive side of the battery pulls the electrons in.

6. Primary Energy Energy sources found in nature that have not been subjected to any conversion or transformation process. Examples: Sunlight, Coal, Natural Gas, wood, oil

7. Secondary Energy Energy which has been transformed from another source. Examples: electricity and gasoline –Electricity is generated by primary sources such as wind, solar, or water –Gasoline is obtained from crude oil

Think about it! *How does energy transformation relate to batteries? *What is the difference between primary and secondary energy? *Why should we use green energy? * How can electric energy be transformed into light energy?

Simple Machines make work easier for us by allowing us to push or pull over increased distances – they allow us to use a lesser force when doing work 7 simple machines –Wheel and axel –Wedge –Inclined plane –Pulley –Gears –Screw –Lever

Mechanical Advantage The difference between the applied force and the work accomplished. Mechanical Advantage = output force input force Example: What is the mechanical advantage if 200J are put in and 50J are produced 50J = J

Work When work is done energy is transferred from one place to another Work is done when the force is applied in the same direction of the motion –Example: Lifting a box is work, pushing a box down the hall is work –carrying a box is NOT work Work = force x distance Work is measured in joules (Joule = Newton x meter or J=1Nm)

Power Power is measured in watts –(1 watt= 1 joule/second) Power = work divided by time (work/time) 1 horsepower = 750 watts Example: A squirrel does 0.50 Joule of work in 2.0 seconds. The power rating of this squirrel is found by: Power = work (.50 J) / time (2 seconds) Power =.25 watts

Efficiency The effectiveness of the machine's performance. The efficiency of a machine is always less than 100% Efficiency = output/input x 100 Example: You do 1200J of work with gears, If the gears do 1000J of work what is the efficiency? 1000/1200 = 0.83 x 100 = 83% efficient A higher efficiency rating is GOOD!!

Formulas Power = work/time Work = force x distance Mechanical advantage = output/input Efficiency = output/input x 100