ENERGY

Energy describes a system’s ability to

cause change.

A system that has energy has the ability to do work.

Mechanical energy is the energy possessed by an object due to its

motion or its position.

Potential energy and kinetic energy are both forms of mechanical energy.

Chemical energy is a form of energy stored in molecules.

Batteries are storage devices for chemical energy.

Electrical energy comes from electric charge,

which is one of the fundamental properties of all matter.

Nuclear energy is a form of energy stored in the nuclei of

atoms.

In the Sun, nuclear energy is transformed

to heat that eventually escapes

the sun as radiant energy.

Radiant energy is energy that is carried by electromagnetic waves.

Light is one form of radiant energy.

The electromagnetic spectrum includes visible light, infrared radiation (heat), and

ultraviolet light.

Light energy and heat energy are included in the electromagnetic spectrum.

The workings of the universe can be viewed as energy flowing from one place to another and changing back and forth from one form to another.

Potential Energy

• Objects that have potential energy do not use the energy until they move.

• An object’s potential energy comes from the gravity of Earth.

• Technically, energy from height is called gravitational potential energy.

• Other forms of potential energy also exist, such as potential energy stored in springs.

Potential Energy

Ep = mgh Height (m)

Mass (kg)

Potential Energy (joules)

Accelerationof gravity (m/sec2)

Systems or objects with potential energy are able to exert forces

(exchange energy) as they change.

Potential energy is energy due to position.

• Energy of motion is called kinetic energy. • The kinetic energy of a moving object

depends on two things: mass and speed.• Kinetic energy is proportional to mass.

Kinetic Energy

• Mathematically, kinetic energy increases as the square of speed.

• If the speed of an object doubles, its kinetic energy increases four times (mass is constant).

Kinetic Energy

EK = ½ mv2

mass of object (kg)

velocity (m/sec)

KE (joules)

Energy of motion is called kinetic energy.

A moving cart has kinetic energy because it can hit another object (like clay) and cause change.

Kinetic energy becomes important in calculating

braking distance.

Pushing a 1-kilogram object with a force of one newton for a distance of one

meter uses one joule of energy.

A joule (J) is the S.I. unit of

measurement for energy.

One joule is a pretty small amount of energy.

An ordinary 100 watt electric light bulb uses 100 joules of energy every second!

Sources of energyThe chemical potential energy stored in the

food you eat is converted into simple sugars that are burned as your muscles

work against gravity as you move.

Systems change as energy flows and changes from one part of the system to another.

Each change transfers energy or transforms energy from one form to another.

As energy takes different forms and changes things by doing work,

nature keeps perfect track of the total.

No new energy is created and

no existing energy is destroyed.

Conservation of EnergyThe idea that energy transforms

from one form into another without a change in the total amount is

called the

law of conservation of energy.

The law of energy conservation says the total energy before the change

equals the total energy after it.

The conservation of energy is most useful when it is applied to a closed system.

Because of the conservation of energy, the total amount of matter and energy in your system stays the same forever.

How can we predict how energy will

change?

One thing we can always be sure of is that systems tend

to move from higher to lower

energy.

• The total energy in the system is the potential energy of the ball at the start.

• Later, the ball is at a lower height (h) moving with speed (v) and has both potential and kinetic energy.

When you throw a ball in the air, the energy transforms

from kinetic to potential and then

back to kinetic.

The word work has a very specific meaning.

Work is the transfer of energy that results from applying a force over a

distance.

Work (joules) = Force (newtons) distance

(meters)W = F d

Regular (incandescent) light bulbs convert

only 10% of electrical energy to

light.

That means 90% of the energy is released

as wasted heat.

Flow of Energy