energy

ENERGY

Potential energy is energy due to position.

Systems or objects with potential energy are able to exert forces

(exchange energy) as they change.

Energy of motion is called kinetic energy.

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

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.

Energy describes a system’s ability to

cause change.

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

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!

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 is energy of position

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

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

• 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)

• 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 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)

Kinetic energy becomes important in calculating

braking distance.

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.

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.

LAW OF CONSERVATION OF ENERGY

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.

Energy in a closed system

• 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.

Conservation of EnergySystems 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.

How can we predict how energy will

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

to move from higher to lower

energy.

Flow of Energy

The 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.

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

from kinetic to potential and then

back to kinetic.

Regular (incandescent) light bulbs convert

only 10% of electrical energy to

light.

That means 90% of the energy is released

as wasted heat.