ENERGY

Essential Question: What is Energy?

AIM: SWBAT define the word “energy” and describe examples of energy.

What is Energy?• Most central concept underlying science• Comes in many forms• Transforms from one form to another• Difficult to describe• Defined as the ability to do work• Like work, it is measured in Joules

When something or somebody moves or jumps or falls or explodes or breathes or thinks or dances or does anything, it's because energy is being transformed.

Work is the transfer of energy through motion. In order for work to take place, a force must be exerted through a distance. The amount of work done depends on two things: the amount of force exerted and the distance over which the force is applied. There are two factors to keep in mind when deciding when work is being done: something has to move and the motion must be in the direction of the applied force. Work can be calculated by using the following formula: Work=force x distance

Work

Kinetic Energy: 1. the energy contained in a moving mass or in a moving particle

2. The conversion of this capability to motion

Potential Energy is 1.stored energy or energy waiting to happen.

2. The capability of doing work.

Types of Energy

Radiant energy is also called electromagnetic energy. Radiant energy is the movement of photons. All life on earth is dependent on radiant energy from the sun. Examples of radiant energy include radio waves (AM, FM, TV), microwaves, X-rays, and plant growth.

Forms of Energy

Radiant Energy

Chemical energy is the energy stored in the bonds of atoms and molecules. This a form of potential energy until the bonds are broken. Fossil fuels and biomass store chemical energy. Products that contain chemical energy include: TNT, baking soda, and a match. Biomass, petroleum, natural gas, propane and coal are examples of stored chemical energy.

Forms of Energy

Chemical Energy

Electrical energy is the movement of elections. Lightning and static electricity are examples of electrical energy that occur naturally. Electric energy can also be stored in man-made sources like batteries.

Forms of Energy

Electrical Energy

Nuclear energy is the energy stored in the nucleus of an atom. Nuclear energy is unusual in that it can give off energy in the form of light or heat, but it is the change in the atom's makeup that produces the energy. Submarines, power plants, and smoke detectors all use nuclear energy.

Forms of Energy

Nuclear Energy

Thermal energy or heat energy is the internal energy in substances. Heat or thermal energy comes from the vibration and movement of atoms and molecules within substance.

Examples; Boiling water, burning wood, and rubbing your hands together really fast.

Forms of Energy

Thermal Energy

Mechanical energy is the movement of machine parts. Mechanical energy is also the total amount of kinetic and potential energy in a system.

Examples: Wind-up toys and grandfather clocks.

Potential energy + Kinetic energy = Mechanical energy

Mechanical Energy

Revisit: Potential Energy• Stored energy - the potential for doing work• Depend on the position and condition of the object.• Think of a stretch rubber band on a slingshot, it has

potential energy due to his position. If the rubber band was placed in a slingshot, it is capable of doing work.

Gravitational Potential Energy• Potential Energy due to elevated positions• GPE of an object is equal to the work done against gravity

in lifting it.• Gravitational potential energy = weight times the height

GPE = mgh

Calculating GPE

• Calculate the change in potential energy of 8 million kg of water dropping 50 m over Niagara Falls.

Calculating GPE• Given: m= 8 million

h = 50 m

g = 9.8 m/s2

• Image:

• Relationship: GPE = mgh• Looking For: Gravitational Potential energy in Joules• Solution: GPE = mgh

=(8,000,000 kg)(9.8 m/s2)(50 m)

= 3,920,000,000 J or 3.92 x109 J

Revisit: Kinetic Energy

• Energy of motion• Depends on the mass and velocity of the object• A moving object is capable of doing work• Kinetic energy = 1/2 mass times the velocity squared.

KE = 1/2 mv2

• KE = to the work required to bring the object to that speed from rest, or the work the object can do while being brought to rest

Fd = 1/2 mv2

Calculating KE• Calculate the kinetic energy of a 3-kg toy cart that

moves at 4m/s.

Calculating KE• Given : m = 3kg v = 4 m/s• Image:

• Relationship: KE = 1/2 mv2

• Looking for: KE in Joules• Solution: KE = 1/2 mv2

= 1/2 (3-kg)(4 m/s)2

= 1/2 (3-kg)(16 m2/s2)

= 1/2 (48 kg.m2/s2)

= 24 kg.m2/s2 or 24 Joules

Law of Conservation of Energy• It states that: Energy cannot be created or destroyed. It

is transformed from one form into another, but the total amount to energy never changes.

• Example - When gasoline combines with oxygen in a car’s engine, the chemical PE stored in the fuel is converted to Molecular KE, or thermal energy. Some of this energy is transferred to the piston and some if this energy causes the motion of the car.

Works Cited• Maslow, G.(2011). Energy [PowerPoint slides]. Retrieved

from http://www.dropbox.com/