ENERGY

Energy describes a system’s ability to

cause change.A system that has energy has the ability to do

work.

ENERGY IS 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!

Systems or objects with potential energy are able to exert forces

(exchange energy) as they change.

Potential energy is energy due to position.

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.

Potential Energy

Ep = mgh Height (m)

Mass (kg)

Potential Energy (joules)

Accelerationof gravity (m/sec2)

Energy of motion is called kinetic energy.

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

• 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

Kinetic Energy

EK = ½ mv2

mass of object (kg)

velocity (m/sec)

KE (joules)

• 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).

Types of energy

POTENTIALENERGY

Chemical energy is a form of energy stored in molecules.

Batteries are storage devices for chemical energy.

TYPES OF ENERGY

Elastic Energy is stored by stretching or

compressing

Electrical energy (static)comes from the build up of charges.

TYPES OF ENERGY

Gravitational Energy is stored due to an object’s

position and mass

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

atoms.

In the Sun, nuclear energy stored in the nucleus of Hydrogen

atoms and is transformed to heat

TYPES OF ENERGY

Types of Energy

KINETICENERGY

Electrical energy (current)comes from electric charge,

which is one of the fundamental properties of all matter.

TYPES OF ENERGY

Light energy is energy that is carried by

electromagnetic waves.

TYPES OF ENERGY

Motion (kinetic) is the energy caused by the movement of an

object from one place to another

TYPES OF ENERGY

Sound energy is transferred by the vibration of

an object

Thermal energy is transferred from a hot object

to a cold object

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.

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.

Kinetic energy becomes important in calculating

braking distance.

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