15.2 Energy Conversion and Conservation 15.2 Key Concepts Can energy be converted from one form to...

15.2 Energy Conversion and Conservation

15.2 Key Concepts

• Can energy be converted

from one form to another?

• What is the law of

conservation of energy?

• What energy conversion

takes place as an object

falls toward Earth?


The movement of a meteor represents what type of energy?

Some of this kinetic energy is converted into heat and light, or _______________ and ___________________ energy

thermalradiant

kinetic


Upon impact, much of the meteor's remaining kinetic energy went into _________________ the rear of this car in Peekskill, New York.

Energy can be converted from one form to another!

crushing


The process of changing energy from one form to another is energy ________________.

Energy Conversion

The striking of a match is a good example.

• Muscles use _______________ energy to move the match.

• Friction between the match and the matchbox converts kinetic energy into _____________ energy.

conversion

chemical

thermal


The thermal energy triggers a chemical reaction on the match tip, releasing some of the match’s ________ chemical energy

This stored chemical energy is converted into ______________ and __________________ energy in the flame

Energy Conversion

stored

thermalradiant


Conservation of Energy

The law of conservation of energy states that energy ______________ be created or destroyed.

It can only change ____________

cannot

form


For example, the work down by friction changes ______________ energy into ______________ energy

Rub your hands against each other for a few seconds…what do you feel?

Recall that friction within machinery ____________ efficiency


kinetic thermal

Heat!

reduces


Even these skaters are subject to friction…they are slowed down by friction with the _________ and the _______________ of the ice.


air surface


Energy Conversions

As an object falls, its _____________ _____________ energy is converted to the ____________ energy of motion. .

Gravitational potential energy

Kinetic energy

gravitational potential

kinetic


One of the most common energy conversions is between potential energy and kinetic energy.

• Example: A coiled spring has

____________ potential energy

when it is compressed

• When the spring expands, it is converted into ______________ energy

Energy Conversions

elastic

kinetic


Some gulls use energy conversion to obtain _______while dropping oysters onto rocks.

The kinetic energy causes the shell to __________ on collision with the rock.

Energy Conversions

food

crack


A pendulum consists of a weight _____________ back and forth from a rope or a string

Pendulum clocks use pendulums to maintain ______________ time.

The time it takes for a pendulum to swing back and forth once is precisely related to its _________.

Energy Conversions

swinging

accurate

length


Where does the pendulum have the greatest potential energy?

Where does the pendulum have the greatest kinetic energy?

Energy Conversions

Highest point of swing

Bottom of swing


Energy Conversion and the Pole VaultIn the pole vault, an athlete uses a flexible pole to propel himself over a high bar.

As the pole bends, some

of the kinetic energy

is converted into

____________

____________ energy

Energy Conversions

elastic

potential


The pole springs back into shape, propelling the pole-vaulter _______________.

• As the pole-vaulter rises, his kinetic energy ______________ while he _________ gravitational potential energy.

• What type of energy

does the pole-vaulter

have at his highest point?

Energy Conversions

upward

decreasesgains

Gravitational p. e.


As he falls, what type of energy does he have?

Energy Conversions

Kinetic energy


Energy Conversion Calculations

Recall that mechanical energy is the __________ kinetic and potential energy of an object

Mechanical energy = KE + PE

When friction is small enough to be ___________, and ______ mechanical energy is added to a system, then the system’s mechanical energy does ______ change.

Energy Conversions

total

ignoredno

NOT


The law of conservation of energy applies to any mechanical process.

If friction can be neglected, the total mechanical energy remains _______________.

Energy Conversions

constant


Conservation of Mechanical EnergyAt a construction site, a 1.50-kg brick is dropped from rest and hits the ground at a speed of 26.0 m/s. Assuming air resistance can be ignored, calculate the gravitational potential energy of the brick before it was dropped.

Mass =

Speed =

Is the brick initially moving?

Energy Conversions

=

1.50 kg

26.0 m/s

noPE = 1/2 (1.50 kg) (26.0 m/s)2

= 507 J


A pendulum with a 1.0-kg weight is set in motion from a position 0.04 m above the lowest point on the path of the weight. What is the kinetic energy of the pendulum at the lowest point? (Hint: Assume there is no friction.)

Mass =

Height =

Energy Conversions

(PE)beginning = mgh = (KE)

1.0 kg

0.04 m

(1.0 kg)(9.8 m/s2)(0.04m) = KE

0.4 J = KE


Energy and Mass

Einstein’s equation,

E = mc2, says that energy and mass are ________________ and can be ____________ into each other.

equivalentconverted


Albert Einstein developed his special theory of __________________ in 1905. This theory included the now-famous equation E = mc2.

• E is _______________• m is _____________ • c is the ________________________ = 3.0 × 108 m/s

A __________ amount of matter can produce

an _____________ amount of energy.

Energy and Mass

relativity

energy

mass

speed of light

small

enormous


Assessment Questions

1. What energy conversion occurs as a result of friction? (think of rubbing your hands)a. chemical energy to thermal energy

b. kinetic energy to potential energy

c. kinetic energy to thermal energy

d. potential energy to thermal energy



2. At what point in a pendulum’s swing does it have maximum kinetic energy?a. the highest point of the swingb. the lowest point of the swingc. halfway between the lowest and highest pointd. same at all positions of the swing



3. According to the law of conservation of mass, energy can be converted from one from to another but not created or destroyed.

TrueFalse

15.2 Energy Conversion and Conservation 15.2 Key Concepts Can energy be converted from one form to...

Documents

Transcript of 15.2 Energy Conversion and Conservation 15.2 Key Concepts Can energy be converted from one form to...