HONORS

Law of Conservation of Energy

• Because of this, it is important to understand all of the different forms energy can take.

• Law of Conservation of Energy: energy can never be created or destroyed, it can only change forms.

Forms of Energy

• Radiant: light that comes from the sun and lightbulbs; used to see and as a power source.
• Also referred to as: solar energy or light energy.
• Thermal: heat that comes from fire, sun, etc.; used to heat objects

Forms of Energy

• Electrical: comes from outlets and power plants; used to power electrical devices.

• Nuclear: comes from releasing energy from the nucleus of an atom; used in nuclear power plants.

• Sound: comes from a variety of sources; used most often for communication

Forms of Energy

• Electromagnetic: form of energy that is reflected or emitted in the form of electrical and magnetic waves that can travel through space.
• Examples: Cell phone, radio, satellite, etc.

Energy Transfers

What are some examples of energy transfers/conversions?

Chemical 🡪 light/thermal/sound

Electrical🡪 Light

Solar 🡪 Electrical

Energy Transfers

What are some examples of energy transfers/conversions?

Electrical 🡪 electromagnetic

(and light and sound)

Kinetic 🡪 Sound

Solar 🡪 Chemical

Photosynthesis

Energy Transfers

• Mechanical energy: the total amount of kinetic and potential energy in a system.
• In a falling object, GPE converts to KE as the object falls.

Mechanical energy remains constant in this system, due to the Law of Conservation of Energy

We can use this idea to do some calculations.

Example #1

Thomas is playing baseball with Matt. Thomas hits the 0.14 kg baseball and it moves with a velocity of 50 m/s. Assuming all energy is conserved, what is the height the ball could reach if hit straight upwards?

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1. What can we find with mass and velocity?
• Start by finding KE of the ball.

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• If all energy is conserved, that means no energy is “lost”, so KE will eventually equal GPE at the peak of the ball’s height. What does this mean we can do?
• Substitute KE for GPE. Then we can rearrange and solve for height.

Example #1

Thomas is playing baseball with Matt. Thomas hits the 0.14 kg baseball and it moves with a velocity of 50 m/s. Assuming all energy is conserved, what is the height the ball could reach if hit straight upwards?

h = ?

m = 0.14 kg

v = 50 m/s

a = 9.8 m/s²

KE = ½ mv²

GPE = ham

am

am

h = GPE

am

KE = ½ (.14)(50)²

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KE = (.07)(2,500)

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KE = 175 J

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Therefore…

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GPE = 175 J

(since all energy is conserved)

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h = 175

(9.8)(.14)

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h = 175

1.372

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h = 127.6 m