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/s2) 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/s2.

• m = 1 kg, g = 10 m/s2, h = 1.5 m• Find PE.• PE = m x g x h• PE = 1 kg x 10 m/s2 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 v2

• KE (joules) = ½ m (kg) x v2 (m2/s2)

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 mv2

• KE = ½ (800kg) x (35 m/s)2

• KE = 490000 J or 490 kJ