# Energy. What is energy?  Every change that occurs… big or small… requires energy.  When something is able to change its environment or itself, it has.

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Energy

What is energy?  Every change that occurs… big or small… requires energy.  When something is able to change its environment or itself, it has energy.  Energy is the ability to cause change.

Examples…  What are some examples of having or using energy?  A moving baseball  Combing your hair  Walking up the stairs

Different Forms  There are different forms of energy.  When you turn on a light, the room gets brighter.  When you turn on your stereo, you hear sound.

Think of money…  If you had \$100, you can keep it…  In your wallet  In a bank account  In travelers checks  In gold and silver coins  The same is true for energy!! It can be found in different forms.

Kinetic Energy  Kinetic energy is energy in the form of motion.  Wheels spinning  A sprinting runner  A train moving

Kinetic Energy  Kinetic energy depends on two quantities…  The mass of the moving object  The object’s velocity

Kinetic Energy  The more mass an object has, the more kinetic energy it has.  The greater an object’s velocity is, the more kinetic energy it has.

Kinetic Energy  Which one has the most kinetic energy? Velocity = 5 m/s Mass = 500 kg Velocity = 20 m/s Mass = 500 kg

Kinetic Energy  Kinetic energy is measured in joules (J)  We use the following equation to calculate how much kinetic energy an object has:  Kinetic Energy = ½ (mass) x (velocity) 2  KE = ½ m v 2  KE (joules) = ½ m (kg) x v 2 (m 2 /s 2 )

Racecar  If a racecar with a mass of 800kg is traveling at 35 m/s… how much kinetic energy does the car have?  KE = ½ mv 2  KE = ½ (800kg) x (35 m/s) 2  KE = 490000 J or 490 kJ

Potential Energy (PE)  Even motionless objects can have energy… the energy is stored in the object.  An apple hanging in a tree has potential energy because it has the ability to cause change, to fall to the ground.  Stored energy due to a position is called potential energy (PE).

Elastic Potential Energy  Elastic potential energy is energy stored by something that can stretch or compress such as a rubber band or a spring.

Chemical Potential Energy  Energy stored in chemical bonds is called chemical potential energy.  Chemical energy is stored in bonds that hold a molecule together and are released when the bond is broken.

Gravitational Potential Energy  Gravitational potential energy (GPE) is stored by objects that are above the Earth’s surface.  The amount of GPE depends on:  The mass of the object  The acceleration due to gravity  The height above the ground

Gravitational Potential Energy  To calculate the GPE of an object, we use the following equation:  GPE = mass x gravity x height  GPE = mgh  GPE (J) = m (kg) x g (m/s 2 ) x h (m)

Changing GPE  The GPE of an object can be changed by changing the height of the object.  When the height of the object is increased, the gravitational potential energy increases!!

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