# Types of Energy Sections 6.3-6.5. What is energy? Energy is the ability to do work Like work, energy is measured in joules (J) What are some examples.

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Types of Energy Sections 6.3-6.5

What is energy? Energy is the ability to do work Like work, energy is measured in joules (J) 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.

Mechanical Energy Mechanical Energies include…. –Potential Energy is energy that arises because of an object’s position –Kinetic Energy is energy of motion possessed by moving objects Mechanical Energy may be in the form of potential energy, kinetic energy, or both.

Potential Energy!!

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 The potential energy that is easiest to visualize is 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: PE = mass x gravity x height PE = mgh PE (J) = m (kg) x g (m/s 2 ) x h (m)

Gravitational Potential Energy Example What is the gravitational potential energy of a 1 kg ball as it sits at the top of a 1.5 m table? Remember gravity = 10 m/s 2. m = 1 kg, g = 10 m/s 2, h = 1.5 m Find PE. PE = m x g x h PE = 1 kg x 10 m/s 2 x 1.5 m 15 J

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!!

Kinetic Energy!!

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? m = 800 kg, v = 35 m/s Find KE. KE = ½ mv 2 KE = ½ (800kg) x (35 m/s) 2 KE = 490000 J or 490 kJ

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