Unit B ReviewScience 24

October 28, 2015

Where does the body get it’s energy??

-The human body converts stored

(potential energy) in food into other

forms of energy

-Exercise speeds up the release of

chemical energy from food stored in the

muscles

-Sleep gives the body’s cells a chance to

clear waste products and renew stores of

energy

Using Energy to Do Work

Potential energy becomes useful

energy when:

-electric energy is converted into

light energy to light your room

-the stored energy in food is

converted to kinetic energy as you

walk out the door

Many Forms of Energy

-Solar energy

-Thermal energy

-Wind energy

-Geothermal energy

Energy Conversions

-energy that enters the system is

called input energy

-The system that changes energy

from one form to another is

called a converter

-The energy that leaves the

system is called output energy

Potential energy from food is

converted to kinetic energy for

muscles to move.

Potential energy from food is

converted to thermal energy

to keep you warm.

Thermal energy can be wasted!

-Think of when a person is

drilling into metal or another

hard material. What happens if

he drills for long periods of

time without stopping?

Conservation of Energy

The Law of Conservation of Energy

states that energy cannot be created

or destroyed. Energy can only be

changed from one form to another.

Input Energy = Output Energy

Energy Conversion Systems

If you touched a light bulb after it has been on for a

while, what would you feel?

A hood on a vehicle feels warm after it has been running

for a while. Why is that? A vehicle is built to get you from

one location to another, not to heat up the hood. So why

is this?

The gas in the tank of a vehicle is full of potential energy.

So why will only a third of it actually be used to move the

vehicle? Where does the rest of the energy go??

Input Energy = useful output energy + waste output

energy

Chapter

6:Electric Energy

at Home

In the early 1800’s, Michael

Faraday discovered that when you

pass a magnet through a coil of

wire, you generate electricity.

Using these observations, he made

the first generator.

A Generator

Input energy converter

output energy

Kinetic energy generator

electric energy

http://www.whatisnuclear.com/articles/nucreactor.html

Electric Energy and Power

Energy is the ability to do work.

Work is defined as force multiplied by

distance.

Work=force x distance

Force is measured in Newtons

1N•m= 1 joule

Power is the rate at which energy is

transferred. Energy= power x time

1 watt= 1 joule of energy per second

Kilowatt hours

Since the watt is a small amount of energy, the

utility companies use a unit of energy 1000x

greater.

One kilowatt hour (kW•h) is equal to 1000 watt

hours.

One appliance that uses 1000 watts in 1 hour uses

the same as a 1 watt light bulb that is on for 1000

hours.

Both use 1kW•h

Efficiency is a measure of how completely

input energy is converted to accomplish the

desired output energy.

Efficiency can be expressed as a percentage.

For example, if a motor is 80% efficient, 80

percent of the input energy is converted to do

the intended job. The other 20% is wasted.

Percent efficiency of an electric device:

useful energy output

total electric energy input X 100

Chapter 7: Energy for Life

-How plants capture energy from

the Sun

-How animals use their food for

energy

-How carbs, fats, and proteins are

used as a source of energy