CONSERVATION OF ENERGY

KINETIC POTENTIALMECHANICAL

ENERGY

the ability to change or move matter

Law of Conservation of Energy: energy cannot be created or destroyed! (It can only change form!)

electrical heat + light

KINETIC ENERGY. . . IS MOVEMENT!

Examples:

Of electrons: ELECTRICAL ENERGY Of electromagnetic waves:

RADIANT ENERGY (x-rays, UV, radio waves, microwaves, etc.)

Of heat: THERMAL ENERGY Of a moving object: MECHANICAL ENERGY

CALCULATING KE:

EQUATION: UNITS:

KE = mv2 mass = kg 2 velocity = m/s

KE = Joules (J)

On your formula chart you will see this as :Kinetic Energy = ½ (mass × velocity2)

SAMPLE PROBLEM:

What is the [kinetic energy] of a 44 kg cheetah running at 31 m/s?

G m = 44 kg, v = 31 m/sU KE = ?E KE = (mv2)/2S KE = (44 kg)(312 m2/s2)/2S KE = 21,142 J

POTENTIAL ENERGY . . . IS STORED OR POSITIONAL!

Examples: In batteries: ELECTRICAL ENERGY In bonds: CHEMICAL ENERGY

(fossil fuels, glucose) In an atom’s nucleus:

NUCLEAR ENERGY In machines: ELASTIC ENERGY

(springs, rubber bands) Of position (height): GRAVITATIONAL

CALCULATING GPE:(Gravitational Potential Energy)

Your Formula Chart shows the formula for GPE as:Gravitational potential energy = mass x acceleration due to gravity x height

EQUATION: UNITS:GPE = mgh mass = kg

acceleration due to gravity = g = 9.8 m/s2

height = m

Weight = mg Weight = Newtons

GPE = Joules

SAMPLE PROBLEM:

What is the GPE of a 2.0 kg rock that sits on the edge of a cliff 12 m high?

G m = 2.0 kg, h = 12 mU GPE = ?E GPE = mghS GPE = (2.0 kg)(9.8 m/s2)(12 m)

S GPE = 235.2 J

MECHANICAL ENERGY

Equals the TOTAL energy in a system!

Is the sum of the PE and the KE.ME = KE + PE

Gradually decreases because of friction

(lost as heat).

Mechanical Energy in a Swinging Pendulum

MAX PE

1. At which point(s) is KE greatest? Why?

1. #3; the faster it moves, the greater its KE.2. #1, #5; the higher it is, the greater its PE.

2. At which point(s) is PE greatest? Why?

MAX PE

MAX KE

http://www.slcc.edu/schools/hum_sci/physics/tutor/2210/potential_energy/

If there is no loss of energy due to friction, the total (mechanical) energy remains the same!

The KE and PE of a roller coaster changes as it travels down the track, depending on its speed and height.

Quiz

Directions: Identify the type of energy described in each problem below. Do not solve the problem.

1. A box on the shelf 2 meters high with a mass of 20 kg.

2. A ball rolling along a shelf that has a velocity of 5 m/s and a mass of 100 g.

3. A marble with a mass of 15 g at the top of a 15 cm tall slope.

4. A weight bar and weights that have a mass of 250 kg lifted up to a height of 2.5 m.

5. An automobile with a mass of 2000 kg and a velocity of 50 m/s.

Quiz (KEY)

Directions: Identify the type of energy described in each problem below. Do not solve the problem.

1. A box on the shelf 2 meters high with a mass of 20 kg. Potential energy

2. A ball rolling along a shelf that has a velocity of 5 m/s and a mass of 100 g. Kinetic energy

3. A marble with a mass of 15 g at the top of a 15 cm tall slope. Potential energy

4. A weight bar and weights that have a mass of 250 kg lifted up to a height of 2.5 m. Potential energy

5. An automobile with a mass of 2000 kg and a velocity of 50 m/s. Kinetic energy

Part 2

Forms of Energy and

Energy Transformation

Forms of Energy

Six forms of energy are:Mechanical EnergyHeat EnergyElectromagnetic EnergyChemical EnergyRadiant EnergyNuclear Energy

Energy Transformation

Energy is always changing from one form to another. – The Sun, primary source of energy on the Earth.

– Nearly all energy comes from the sun.

– Energy cannot be created or destroyed. (AKA: Law of Conservation of Energy)

The Flow of Energy

The Sun,

Nuclear

Energy

Earth

Energy received by the Earth is converted into heat and chemical energy.

The Sun gives off Radiant energy in the form of light

The Flow of Energy

Plants convert light (radiant energy) into chemical energy (sugar or glucose) through a process called Photosynthesis.

When light from the Sun hits the Earth the radiant energy is transformed into heat energy.

Energy Transformation

There are many examples of energy transformations. Give an example for each arrow in the following diagram.

Electromagnetic Radiant

Chemical

NuclearMechanical

Heat

Energy