April 18, 2023

Energy Conversion and Conservation Notes

Which of the following is a measure of the ability to do work?1. Power2. Energy3. Photosynthesis4. Joules

Power

Ener

gy

Photo

synth

esis

Joule

s

0%

33%

0%

67%

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I.) Energy ConversionA) Energy Conversion

1) Energy can be converted from one form to another.

2) Can take place in a series of steps (Ex: striking a match)

B) Conservation of Energy1) The law of conservation of energy states that energy cannot be created or destroyed. (Energy lost = Energy gained)

2) The amount of energy in the beginning must be same amount at the end.

a) Example: Riding a bike1) When you stop pedaling, the

bike will eventually stop. Where does the KE go? Frictional forces act on the bike and turn KE into thermal energy

C) Energy Conversions1) Most common conversion is between PE and KE

2) The gravitational PE of an object is converted to the KE of motion as object falls. (Ex: Avalanche)

3) Energy conversions in Pendulumsa) KE and PE undergo constant conversion in a pendulum

PE is greatest

KE = 0

KE is greatest

PE = 0

PE is greatest

KE = 0

Mechanical vs Nonmechanical Energy (write somewhere on your notes- no blanks!)

1. Mechanical Energy- Energy you can

“see”

* If something has mechanical energy you can see it move (or you would see it move if it only has potential energy)

Non-mechanical Energy- energy you cannot “see”

Exs- Energy between atoms in a molecule

apples give energy when eat them*Non-mechanical energy can be heat

energy, light energy (electromagnetic), chemical energy, or nuclear energy.

*Once again, you CANNOT SEE non-mechanical energy

4) Calculations-Mechanical Energy = sum of the KE + PE in the components of a mechanical system

-Conservation of Mech. Energy:

(KE + PE)beginning = (KE + PE)end

D) Energy and Mass

E = mc2

1) Einstein’s equation, E=mc2, says that energy and mass are equivalent and can be converted into each other.

II.) Transfer of Thermal Energy

A) Conduction: the transfer of energy through direct contact of a material1) This occurs within a material or between materials that are touching2) Conduction in gases is slower than in liquids and solids because the particles collide less often in a gas

3) Thermal conductor: transfer of heat energy through a material

a) Examples: -Wire rack in hot oven- Tile floor

4) Thermal Insulator: material that is a poor conductor of heat and therefore reduces energy transfer

a) Examples: -Wooden spoon- Air- Styrofoam

B) Convection: the movement of matter due to differences in density that are caused by temperature variations1) Particles can transfer thermal energy from hot to cold area2) Example: Oven

-Temp is higher at bottom of the oven- Air at bottom heats up & is then less

dense-HOT air RISES- The air that was at the top, cools off &

is then more dense-COLD air SINKS

3) Convection current: the vertical movement of air currents due to temperature variation

a) Convection currents are important in many natural cycles, such as ocean currents, weather systems, and movements of hot rock in Earth’s interior.

C) Radiation: the energy that is transferred as electromagnetic waves, such as visible light & infrared waves1) Examples: - Sun

- Standing by grill & feel the heat- Heat lamp in restaurant

Which of the following does a flying Frisbee have the most of?

9%

77%

9%

5% 1. Mechanical potential energy2. Non-mechanical potential energy3. Mechanical kinetic energy4. Non-mechanical kinetic energy

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Which of the following best describes the motion of the atoms in a cup of hot chocolate?

58%

0%

42%

0% 1. Mechanical potential energy2. Non-mechanical potential energy3. Mechanical kinetic energy4. Non-mechanical kinetic energy

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Which of the following best describes a wound up clock spring?

5%

5%

23%

68% 1. Mechanical potential energy2. Non-mechanical potential energy3. Mechanical kinetic energy4. Non-mechanical kinetic energy

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Which of the following best describes a clock spring unwinding?

0%

92%

4%

4% 1. Mechanical potential energy2. Non-mechanical potential energy3. Mechanical kinetic energy4. Non-mechanical kinetic energy

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Which of the following best describes a skateboarder sitting at the top of a hill?

4%

0%

50%

46% 1. Mechanical potential energy2. Non-mechanical potential energy3. Mechanical kinetic energy4. Non-mechanical kinetic energy

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Which of the following best describes the energy within the bonds between the atoms in a bowl of cereal?

9%

9%

82%

0% 1. Mechanical potential energy2. Non-mechanical potential energy3. Mechanical kinetic energy4. Non-mechanical kinetic energy

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Why does a dropped tennis ball not return to its original position?

23%

36%

14%

27% 1. Energy is lost2. Nonmechanical energy is converted to

mechanical energy3. Mechanical energy is converted to

nonmechanical energy4. There is not enough potential energy

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A boulder has 600 J of PE. Ignoring air resistance, approximately how much KE does it have right before it hits the ground?