Potential and Kinetic Energy

• Energy is the ability to do work
• We can see energy as light and hear it as sound

Forms Of Energy

• There are two main forms of energy: potential and kinetic
• Potential energy is the energy possessed by an object because of its position, or vertical separation from the ground
• The amount of potential energy depends on the height of an object relative to a reference point
• Potential energy value can be negative, positive, or zero
• Examples of potential energy: a stretched bow, a golf ball sitting on a tee, and a hockey puck sitting on the ice
• Kinetic energy is the energy an object possesses due to its motion
• If an object moves faster, it has more kinetic energy
• The amount of kinetic energy depends on the object's mass and speed
• Kinetic energy has only two values: zero when the object is not moving, and positive when the object is moving
• Examples of kinetic energy include a basketball thrown in the air, a bicycle in motion, and a moving volleyball during a game
• A stationary bike on top of the hill has stored potential energy
• When the bike starts moving downhill, its potential energy transforms into kinetic energy

Potential Energy Types

• Gravitational energy is the energy stored in an object's position, and its amount depends on its height and mass
• Dams accumulating water from rivers to reservoirs are an example of hydropower, which is gravitational energy
• Chemical energy is the energy stored in the bonds of atoms and molecules
• Examples of chemical energy are ordinary batteries, biomass, petroleum, and natural gas
• Burning wood or gasoline converts chemical energy to thermal energy
• Nuclear energy is the energy that holds the nucleus together and is stored in the nucleus of an atom
• When nuclei combine (fusion) or split apart (fission), large amounts of energy are released
• Nuclear power plants use uranium fission, and the sun uses hydrogen fusion to generate electricity
• Mechanical (elastic) energy is possessed by objects under tension, like compressed springs and stretched rubber bands
• Elastic energy stored in a bow is transferred to the arrow upon release, converting it to kinetic energy

Kinetic Energy Types

• Motion energy is energy stored in the movement of objects, affected by the object's speed and mass
• Wind is an example of motion energy
• Heat (thermal) energy is due to the vibration and movement of atoms and molecules within substances
• Heating an object increases the motion and collision of its atoms and molecules
• Earth's thermal energy can be harnessed by geothermal power plants
• Radiant energy is electromagnetic energy that travels in transverse waves
• Types of radiant energy include visible light, X-rays, gamma rays, and radio waves
• Sound energy is the movement of energy through substances in longitudinal waves, produced when force causes vibration
• Electrical energy is delivered by tiny charged particles called electrons moving through a wire
• Lightning is a natural example of electrical energy

Energy Transformation Examples

• Talking on a phone transforms electrical energy to sound energy
• Eating transforms chemical energy to thermal energy
• A bike moving downhill, transforms potential energy into kinetic energy

Law of Conservation of Energy

• Energy transforms from one form to another, but is neither created nor destroyed; it has always existed in one form or another
• Energy before = energy after
• mgh = 1/2mv²

Example Problems

• A 0.5 kg ball is tossed upward with a kinetic energy of 100 J. How high does the ball travel?
• The kinetic energy is 200 J at the bottom of its motion, what will be its maximum height if it weighs 4 kg?
• A 1 kg ball falls from a height of 5 meters, what is its kinetic energy just before hitting the ground?
• A 500 kg roller coaster starts from rest at the top of an 80 m hill assuming the track is frictionless, what is the roller coaster's velocity at the bottom of the hill?
• A 400 kg bike starts from rest at the top of a 90 m hill, what is the bike's velocity at the bottom of the hill?