Post on 02-Jan-2016
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 = .25
200J
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