Energy- Topic14(I.) Forms of energy (see video “forms of energy” on my website) kinetic energy- the energy of motion thermal energy- all objects store thermal energy the higher the temperature, the more thermal energy light energy sound energy elastic potential energy- when a springy material stretches or compresses (a bungee cord, bow and arrow nuclear energy- energy stored in the nucleus of an atom (this powers the sun, nuclear power plants, bombs)gravitational potential energy- objects gain gravitational potential energy when lifted above the ground chemical energy- stored in the bonds of chemicals (ex. Food, fuel like coal) electrical energy – electrons flowing thru a wire

Energy- Topic14(I.) Forms of energy (see video “forms of energy” on my website) kinetic energy- thermal energy-

light energy sound energy elastic potential energy-

nuclear energy-

gravitational potential energy-

chemical energy-

electrical energy –

Energy Demos- Notes Topic14Alka Seltzer demo:

2 beaker demo:

Raquetball demo:

Wymhurst Machine:

Mass suspended from the ceiling:

Silently Read Pages (172 - 178 ) of text

• Fill out concept chart

Topic 14- Energy formulas

• The two main types of energy we will need to be able to calculate are kinetic energy and gravitational potential energy

Kinetic Energy

Equation Units

KE = ½mv2

The Energy of Motion

KE = ½(mass)x(velocity)2

Joules (J)

kgm2/s2

If the object is moving it has Kinetic Energy Ask … “Is it moving?”

Potential Energy

Equation

The Energy of Position

PEg = mgh

PEg=(mass)x(gravity)x(height)

Units

Joules (J)

kgm2/s2

If the object is above the ground it has Potential Energy Ask … “Is it above the ground?”

Notes topic 15

• Energy can change form

Wiley coyote

• http://bit.ly/pY8h6o• http://www.wimp.com/gomachine/

• http://www.tokyomango.com/tokyo_mango/2007/05/rube_goldberg_m.html

• http://bit.ly/pY8h6o• http://www.wimp.com/gomachine/

• http://www.tokyomango.com/tokyo_mango/2007/05/rube_goldberg_m.html

• http://bit.ly/pY8h6o• http://www.wimp.com/gomachine/

• http://www.tokyomango.com/tokyo_mango/2007/05/rube_goldberg_m.html

http://www.physicsclassroom.com/

mmedia/energy/ce.cfm• What do you notice about the green bar?

“The Conservation of Energy”

The Conservation of Mechanical Energy

Kinetic and Potential Energy

To identify each type of Mechanical Energy ask the following questions:

• Kinetic Energy: (KE)– Is the object moving?

• Gravitational Potential Energy: (PEg)– Is the object above the ground?

• Elastic Potential Energy: (PEe)– Is a spring compressed or an elastic stretched out?

Note: Point 1 is the highest and Point 2 and 4 are “on the ground”

Look at the rollercoaster below.- Question 1 Identify if the rollercoaster car has Gravitational Potential Energy, Kinetic Energy or both at each point.

Note: Point 1 is the highest and Point 2 and 4 are “on the ground”

Look at the rollercoaster below. Identify if the rollercoaster car has Gravitational Potential Energy, Kinetic Energy or both at each point. Fill in the table identifying the amount of kinetic and potential energy for each point.

PEg

KE

KE + PEg

KE

KE + PEg

Point 1 Point 2 Point 3 Point 4 Point 5

PEg 750 J 600 J

KE 400 J

ME

Question2

Point 1 Point 2 Point 3 Point 4 Point 5

PEg 750 J 600 J

KE 400 J

ME

0 J

750 J 750 J 750 J 750 J 750 J

150 J

350 J0 J

750 J

0 J

750 J

Quick Video Clip

• http://www.teachersdomain.org/asset/mck05_int_rollercoaster/

The Law of the Conservation of Mechanical Energy – Topic 15 states that Energy can convert

from one form to another form but in the absence of friction total ME stays same!

Identify the types of Mechanical Energy the object has at each point.

Identify the types of Mechanical Energy the object has at each point.

PEg (above the ground)

KE(moving)

PEg (above the ground)

KE(moving) KE

(moving)

Conservation of Mechanical Energy

• In the absence of friction, in a closed system the total mechanical energy (sum of the potential and kinetic energy) remains constant.

Energy transformation of a downhill skier

• http://www.physicsclassroom.com/mmedia/energy/se.cfm

Problem #4 An 18 kg rock falls from a height of 5.0 m. What is the gravitational potential energy it has initially?

Problem #5 Assignment #13An 18 kg rock falls from a height of 5.0 m. What is the gravitational potential energy and the kinetic energy when it is 2.5m above the ground?

Problem #6The same 18 kg rock falls from a height of 5.0 m. What is the kinetic energy it has as it hits the ground?

The Law of the

Conservation of Mechanical Energy

Pendulum

“bob”

http://www.physicsclassroom.com/mmedia/energy/pe.cfmAnimation of a pendulum

The Law of the

Conservation of Mechanical Energy

Pendulum

“bob”

Mechanical Energy is conserved when no dissipative forces are present.

Total mechanical energy stays the same as long as there is no friction!

PEg

KEKE + PEg

PEg = 500J

= 500J = 500J

= 500J

Pendulum animated

• http://www.physicsclassroom.com/mmedia/energy/pe.cfm

Problem #1 Calculate the potential energy of the 10kg rock at the top of a 20m high cliff.What is the kinetic energy of the rock at the bottom of the cliff?

Problem #1 Calculate the potential energy of the 10kg rock at the top of a 20m high cliff.What is the kinetic energy of the rock at the bottom of the cliff right before it hits the ground?

PE = ?m = 50kgh = 30mPE

KE

PE = mghPE = (10kg)(9.8m/s2)(20m)

PE = 1960 J

MEtop = MEbottom

PEtop = KEbottom

1960J = KE

=1960J

=1960J

Problem #2Calculate the kinetic energy of the 10kg person moving at 5m/s at the bottom of a hill.What is the potential energy of the person at the top of the hill?

Problem #2Calculate the kinetic energy of the 10kg person moving at 5m/s at the bottom of a hill.What is the potential energy of the person when they come to rest at the top of the hill?

KE

PE

KE = ?m = 10kgv = 5m/s

KE = ½mv2

KE = ½ (10kg)(5m/s)2

KE = 125 J

MEtop = MEbottom

KEbottom = PEtop

125J = PE=125J

=125J

Law of conservation of mechanical energy

In the absence of friction, in a closed system the total mechanical energy (sum of the potential and kinetic energy) remains constant.