Unit 2 Unit 2 Chapter 6Chapter 6

Section 1 : Energy Section 1 : Energy ChangesChanges

What is Energy?What is Energy? The word The word energyenergy comes from the comes from the

Greek word “EnergosGreek word “Energos” which ” which means means activeactive

EnergyEnergy is the ability to is the ability to cause cause changechange

•For example:

•Energy can change the temperature of water.

•Energy can change the direction and speed of a baseball .

•The energy in a thunderstorm produces lightening that lighten up the skies and thunder that rattle windows

Forms of energy Forms of energy Energy comes in different forms Energy comes in different forms

from many sources.from many sources.

Food provides energy in the form of Food provides energy in the form of chemical energy.chemical energy.

Your body Your body convertsconverts the the chemical chemical energyenergy in the food you eat in the food you eat into the into the energy it needs to moveenergy it needs to move

Energy Energy TransformationsTransformations

•Energy Transformation occurs if energy changes from one form to another .

•When the car sits in sunlight all day the energy in sunlight changes to heat energy that warms the inside of the car

•Chemical energy is stored inside your muscles.

•When you push down on a bicycle pedal , chemical energy is used to make your legs move.

•The chemical energy stored in your muscles is transformed to energy of motion

During energy transformation the During energy transformation the total amount of energy remains the total amount of energy remains the same.same.

Energy is never lost or gained it only Energy is never lost or gained it only changes formchanges form

Using energy transformation

An electric current that flows in a wire carries electrical energy that can be used in several

ways A hair dryer converts electrical energy into heat energy.

A light bulb converts electrical energy into heat and light energy

Kinetic energy:Kinetic energy:

It’s the energy an object has due It’s the energy an object has due to motionto motion

Example:Example:

A moving bowling ball has energy A moving bowling ball has energy that causes the pins to fall .that causes the pins to fall .

This energy is called kinetic This energy is called kinetic energy.energy.

Kinetic Energy

The sky diver has kinetic energyA ball kicked by a football player has a kinetic energy

Mass, Speed and Kinetic Mass, Speed and Kinetic EnergyEnergy All moving objects have kinetic All moving objects have kinetic

energy.energy.

Not all moving objects have the Not all moving objects have the same amount of kinetic energy.same amount of kinetic energy.

The The amountamount of of kinetic energykinetic energy an an object has depends on the object has depends on the massmass and the and the speed speed of the objectof the object

Imagine those two rocks are rolling down the hillside with the same speed.Which one will have more kinetic energy?

Which one will cause more damage if they hit something at the bottom?

The larger rock could cause more damage because it has larger mass and has more kinetic energy than the smaller rock

Kinetic energy also depends on speed .The faster object has more speed and has more kinetic energy

Transferring kinetic energyTransferring kinetic energyKinetic energy could be transferred from one object to another when they collide .

•The bowling ball does not touch all the pins but it can knock them down with one roll .

•The bowling ball transfer kinetic energy to few pins.

•The pins will transfer this kinetic energy to each other and knock them down

•A transfer of kinetic energy takes place when dominos fall.

•When you tap the first domino you give it a kinetic energy

•Then the domino will fall into the next one and the kinetic energy will be transferred from one domino to another

This skater has no kinetic energy as she’s standing at the top of the hill and not moving.

As the skater moves down , she is moving faster and her kinetic energy increases.

Remember:Energy can not be created nor destroyed, so where does this kinetic energy come from?

Gravity pulls the skater Gravity pulls the skater down the hill.down the hill.

If the skater was standing If the skater was standing at the bottom of the hill, at the bottom of the hill, gravity wouldn’t start her gravity wouldn’t start her moving.moving.

When the skater is at the When the skater is at the top of the hill, she has a top of the hill, she has a form of energy calledform of energy calledPotential energyPotential energy

Potential EnergyPotential Energy It’s the energy that is stored because It’s the energy that is stored because

of an object’s position.of an object’s position.

The Higher an object is lifted above The Higher an object is lifted above earth, the greater is it’s potential earth, the greater is it’s potential energyenergy

Converting potential and Converting potential and kinetic energykinetic energy

When you throw a ball upwards it is moving the fastest so it has maximum kinetic energy

As the ball moves upward , it slows down and stops for an instant

As the ball moves downward it speeds up and the potential energy is transferred into kinetic energy

Energy changes in falling Energy changes in falling waterwater

Is converted to

Water at the top of the dam has potential energy.

When water falls downwards the potential energy changes into kinetic energy

The kinetic energy in the moving water spins the generators and that’ll produce electrical energy

Law of conservation of Law of conservation of energyenergy

“Energy cannot be created or destroyedit only can be transformed from one form into another”

So, The total amount of So, The total amount of energy never changesenergy never changes, it only changes form, it only changes form