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Energy. Kinetic and potential. ENERGY. Standard: S8P2 a.Explain energy transformation in terms of the Law of Conservation of Energy. b. Explain the relationship between potential and kinetic energy. Energy can be classified as potential or kinetic. Potential energy: energy of position.

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Energy

Energy

Kinetic and potential


Energy1

ENERGY

Standard: S8P2

a.Explain energy transformation in terms of the Law of Conservation of Energy.

b. Explain the relationship between potential and kinetic energy.


Energy can be classified as potential or kinetic

Energy can be classified as potential or kinetic

  • Potential energy: energy of position

The boulder has

more gravitational

potential energy when

measured from point A

compared to B.

PE = mgh


Pe mgh

PE = mgh

  • m = mass in kilograms

  • g = acceleration due to gravity

    (9.8 m/s2)

  • h = height in meters

  • Potential Energy is measured in

    kg • m/s2• m =

    newton meter =

    Joules


Example 1

Example 1:

  • If the boulder has a mass of 8kg, and distance B is 10m, what is the potential energy of the boulder relative to the plateau?

8kg

10m


Answer

Answer:

  • PE = mgh

  • = 8kg • 9.8m/s2 • 10m

  • =784 J

8kg

10m


Example 2

Example 2:

  • If distance A is 20m, what is the potential energy of the boulder relative to the bottom?

8kg

20m


Answer1

Answer:

  • PE = mgh

  • = 8kg • 9.8m/s2 • 20m

  • = 1568 J

8kg

20m


Example 3

Example 3

  • When work is done to stretch something, it is called elastic potential energy.

Find the elastic potential energy stored in a drawn bow if it takes an average force of 100N to pull the arrow back a distance of 0.5 meters.


Answer2

Answer:

  • PE = mgh = Fd

Fxd = 100N x 0.5m

= 50J


Kinetic energy

Kinetic energy

  • Energy of motion

  • KE = ½ mv2


Ke 1 2mv 2

KE = 1/2mv2

  • m = mass in kilograms

  • v = velocity in meters/sec

  • Kinetic energy is measured in

  • kg • m/s • m/s =

  • kg m/s2 • m =

  • newton meter =

  • Joules


Example 4

Example 4

  • The bird has a mass of 2 kg. It is flying at a speed of 5 m/s. Find its kinetic energy.

  • KE = ½ mv2

  • = ½ • 2kg • (5m/s)2

  • = ½ • 2kg • 25 m2/s2

  • = 25 joules


Kinetic and potential energy conversions

Kinetic and potential energy conversions

  • Describe the energy conversions in this picture:

  • At the top:

  • ¼ of the way down:

  • ½ way down:

  • ¾ down

  • At the bottom:

  • Is the sum of KE + PE a constant?

All PE, no KE

3/4 PE, 1/4 KE

1/2 PE, 1/2 KE

1/4 PE, 3/4 KE

No PE, All KE

Yes! It’s always

10,000 J in this case.


Where are pe and ke maximums in this picture

Where are PE and KE maximums in this picture?

PE

and KE

Max PE

no KE

Max KE

No PE

Max PE

No KE


Energy

What happens when the cord is cut?

Potential energy

is converted to

kinetic energy!


Kinetic and potential energy convert to one another

Kinetic and potential energy convert to one another

PE max

PE max

no KE

no KE

KE max

KE max

no PE

no PE


How is mass related to energy

How is mass related to energy?

  • Albert gave us the answer!

E=mc2


E mc 2

E=mc2

  • E = energy in joules

  • m = mass in kilograms

  • c = speed of light

  • (3 x 108 m/s)


A small mass gives a great amount of energy

A small mass gives a great amount of energy


Nuclear energy clean power for the world

Nuclear energy- clean power for the world?


Example

Example:

  • How much energy can be given off by 5 grams of mass? ( 10 paper clips = 5 g)

  • 5g = 0.005 kg

  • E=mc2

  • = 0.005kg x (3 x 108 m/s)2

  • = 0.005 kg x 9 x 1016 m2/s2

  • = 0.045 x 1016

  • = 450,000,000,000,000 J


Energy

WOW!!!

  • 450,000,000,000,000 J is the amount of energy in 3 million gallons of gasoline!


Energy

Einstein's theories of

relativity have been

proved during solar eclipses.

Light is bent by

gravity


Energy

See ya!

The End


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