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