Types of Energy Sections

What is energy? Energy is the ability to do work Like work, energy is measured in joules (J) Forms of energy- light, heat, sound electricity and radioactivity What are some examples of having or using energy? –A moving baseball –Combing your hair –Walking up the stairs

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 When you turn on a light, the room gets brighter. When you turn on your stereo, you hear sound..

Mechanical Energy Mechanical Energies include…. –Potential Energy –Kinetic Energy Mechanical Energy may be in the form of potential energy, kinetic energy, or a combination of both.

Potential Energy!!

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

Other Forms of Potential Energy Elastic potential Energy Chemical potential energy

Gravitational Potential Energy We focus most on gravitational potential energy. Gravitational potential energy (GPE) is stored by objects that are above the Earth’s surface affected by gravity. 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. KNOWN: m = 1 kg g = 10 m/s 2 h = 1.5 m Find PE. EQUATION: PE = m x g x h WORK: PE = 1 kg x 10 m/s 2 x 1.5 m  15 J

Another example If the PE of a ball is 30 J and it is at a height of 3 m what is the mass of the ball? KNOWN: PE=30 J g= 10 m/s 2 h=3 m Find mass EQUATION: PE = m x g x h OR m= PE/g x h WORK: 30 J = m x 10 m/s 2 x 3 m 30 J = m x 30 (divide both sides by 30) 30 J / 30 = m x 30 / 30  1m

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!!

Which has more Potential Energy Boy sitting in a tree 12 feet off the ground OR Squirrel sitting in a tree 12 feet off the ground Squirrel sitting in a tree 30 ft. in the air OR Squirrel sitting in a tree 12 ft. In the air

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? KNOW: m = 800 kg, v = 35 m/s Find KE. EQUATION: KE = ½ mv 2 WORK: KE = ½ (800kg) x (35 m/s) 2  KE = J or 490 kJ

Another Example If a racecar with a mass of 400kg is traveling with a KE of 5,000 J… What is the speed of the car? KNOW: m = 400 kg KE= 5, 000 J Find KE. EQUATION: KE = ½ mv 2 WORK: 5,000 J = ½ (400kg) x (V) 2 5,000 J / 200 kg = V 2 25 = V 2 Take the square root of 25  V = 5 m/s

Triple Check your Knowledge The amount of potential and kinetic energy in a moving swing is always ___________, whereas the amount of mechanical energy is _______________. Remember mechanical energy is the sum of the energy taking place. Changing The same

The Bouncing Ball Fill in the diagram of the bouncing ball with Kinetic and potential energy PE= 100 J KE= 0 J PE= 0 J KE= 100 J PE= 50 J KE= 50 J PE= 50 J KE= 50 J PE= 0 J KE= 100 J

SWING VIDEO Sport