Kinetic and Potential Energy

After the Lesson:• You will be able to define and identify

Kinetic and Potential energy.• You will be able to give examples of

the two forms of energy.• You will be able to explain how one

can transfer to the other.

Definition of Energy…

The ability or capacity to do work.

Measured by the capability of doing work:

potential energy or

the conversion of this capability to motion:

kinetic energy.

Kinetic Energy Potential Energy

Radiant ElectricalChemical

Thermal NuclearMagnetic

Sound

Mechanical

Potential Energy…

• Energy due to position or stored energy.

Potential energy is calculated by:The object’s weight, multiplied by the earth's gravitational pull (9.8 m/sec sq), multiplied by the distance the object can fall.

Potential energy exists whenever an object which has mass has a position within a force field. The most everyday example of this is the position of objects in the earth's gravitational field. The potential energy of an object in this case is given by the relation:

PE = mgh

 PE = Energy (in Joules)

m = mass (in kilograms)

g = gravitational acceleration of the earth (9.8 m/sec2)

h = height above earth's surface (in meters)

POTENTIAL ENERGY

Examples of Potential Energy:

Stretching a rubber band.. -Stores energy

Water at the top of a waterfall.. -Stores energy

Yo–Yo in held in your hand.. -Stores energy because of position

Drawing a Bow… -Stores energy because of position

• When the position of an object is altered it, creates Potential Energy.

• A yo-yo on the table, doesn’t have energy, but when picked up, it alters its position and now it has the ability (or potential) to do work.

• A bow doesn’t have the capacity to do work, unless it’s held at an elevated position.

Definition of Kinetic Energy…

The energy of motion.

Kinetic energy is calculated by one half of the object’s mass,

multiplied by the object’s speed- squared.

The greater the mass or velocity of a moving object, the more kinetic energy it has.

Kinetic Energy Lab

KINETIC ENERGY

Examples of Kinetic Energy…

• Shooting a rubber band.

• Water falling over the fall.

• A Yo-Yo in motion.

• Releasing the arrow from the bow.

Potential Energy Converted to Kinetic

Energy…

When stored energy begins to move, the object now transfers from potential energy into kinetic energy.

Standing still Running

What happens when the cord is cut?

Potential energyis converted tokinetic energy!

•Potential Energy-–“stored” energy–related to an object’s height above the ground

–the higher something is, the more potential energy it has

•Kinetic Energy-–“energy of motion”–related to an object’s velocity–the faster something is traveling, the more kinetic energy it has

•Decide whether each slide is an example of potential or kinetic energy.

•Click on your answer to see if you are correct.

Whenever you see this picture, you will need to write the answer in your journal.

The Ball

PotentialEnergy

Kinetic Energy

The Ball

PotentialEnergy

Kinetic Energy

KineticEnergy

Potential

Energy

KineticEnergy

Potential

Energy

PotentialEnergy

Kinetic Energy

PotentialEnergy

Kinetic Energy

KineticEnergy

Potential

Energy

KineticEnergy

Potential

Energy

PotentialEnergy

Kinetic Energy

PotentialEnergy

Kinetic Energy

• Conservation of energy says that the amount of energy the coaster has will always be constant. This means the potential energy of the car plus the kinetic energy of the car must always be the same. If the potential goes up, the kinetic must come down; if the kinetic goes up, the potential must come down.

The Hill: Conservation of Energy

Why is the first hill of the roller coaster always the

highest?

At the top of the first hill:

• Kinetic Energy?– The coaster’s velocity is zero . . .– Kinetic energy = 0

• Potential Energy?– The coaster is very high . . .– Potential energy = high

• All of the coaster’s energy is in the form of potential energy.

At the bottom of the hill:

• Kinetic Energy?– The coaster is moving at a high

velocity.– Kinetic energy = high

• Potential Energy?– The height of the coaster is zero . . .– Potential energy = 0

• By the time the coaster reaches the bottom of the hill, all potential energy has been transformed to kinetic energy.

But why is the first hill highest?

• When the coaster reaches the bottom of the first hill, all its energy has been transformed from potential to kinetic energy.

• As it goes up the next hill, that kinetic energy must be transformed back into potential energy so the process can repeat.

• But don’t forget friction – the coaster is always losing energy to friction between the car and the tracks, so each time it goes up a hill it will have less kinetic energy to transform back into potential.

The first hill of a roller coaster always must be the highest, otherwise the coaster won’t have enough energy to get up the other hills.