Energy and Energy Resources

Chapter 5 Sections 1-3

pages 124-141

Energy and Work

• Energy: the ability to do work

• Work is done when a force causes an object to move in the direction of the force

• Energy can be transferred

• Expressed in the unit of Joules (J)

Kinetic Energy

• Kinetic Energy- energy of motion

• All moving objects have kinetic energy

• Used to do work• Find with the equation:KE = mv²

2• KE Mass (m), Speed (v²)

Math Focus KE = mv² 2

• 1. {2400 kg x (20 m/s)²}2

• KE= 480,000 J it has twice the KE• 2. {4000 kg x (2 m/s)²}

2• KE = 8,000 J• {4000 kg x (4 m/s)²}

2• KE = 32,000 J

• 3. {2000 kg x (30 m/s)²}2

• KE= 900,000 J• 4. {3000 kg x (20

m/s)²}2

• KE= 600,000 J

Potential Energy

• Potential energy is the energy an object has because of its position

• The amount of gravitational potential energy that an object has depends on its weight and its height

Gravitational Potential Energy

• Depends on weight and height

• Formula:Gravitational Potential energy = Weight (N) x height (m)• Units- either N/m or Joules• The height you use to

calculate is the measure of how far an object has to fall

Math Focus pg 126

• 1. 40 N x 0.8 m = • 32 J• 2. 500 N x 10 m• 5000 J• 3. 600 N x 8 m• 4800 J

Mechanical Energy

• The total energy of motion and position of an object. (potential and kinetic are examples)

• Mechanical energy = potential + kinetic

• Mechanical energy of an object remains the same unless it transfers some of its energy to another object.

Other forms of Energy

• Thermal Energy is all kinetic energy due to random motion of the particles that make up an object. Fast movement, a lot of energy (steam).

• Chemical Energy is the energy of a compound that changes as its atoms are rearranged. Chemical energy is a form of potential energy because it depends on the position and arrangement of the atoms in a compound. Food

• Electrical Energy is the energy of moving electrons. Negatively charged particles move around to produce energy when plugged in, so it is potential energy until used.

• Sound Energy is caused by an object’s vibrations. These vibrations are carried through the air. The potential energy of the strings is turned into kinetic energy when you strum the string.

Other forms of Energy

• Light Energy is produced by the vibrations of electrically charged particles. This causes energy to be transmitted.

• Nuclear energy is the energy that comes from changes in the nucleus of an atom. Atoms have a lot of potential energy, when their nucleus splits (fission) or combines (fusion) then a lot of energy is given off as kinetic energy.

Energy Conversions

• An energy conversion is the change from one form of energy to another.

• Most times one form of energy changes into more than one form.

Kinetic and Potential Energy

• Figure 1- the conversion of potential to kinetic and back again. Skateboarder on the ramp/using a pendulum

• Elastic potential energy: stored energy that is released when the rubber band goes back to its original shape.

Conversions involving Chemical Energy

• Chemical energy of food is converted into kinetic energy when you are active, it is converted to thermal energy to maintain body temperature.

• Photosynthesis uses light energy to make new substances that have chemical energy.

The Process Continues

• Plants change light energy into chemical energy

• That chemical energy in the food you eat changes into another kind of chemical energy

• Your body uses this chemical energy into kinetic energy

Why energy conversions are important..

Alarm Clock Electrical Energy → Light Energy and Sound Energy

Battery Chemical Energy → Electrical Energy

Light Bulb Electrical Energy → Light Energy and Thermal Energy

Blender Electrical Energy → Kinetic Energy and Sound Energy

Energy and Machines

• A machine can make work easier by changing the size or direction (or both) of the force needed to do work.

• Example is a radiometer can convert light energy into kinetic energy.

Conservation of Energy

• Roller coaster cars go up and down the hills converting some potential into some kinetic energy.

• No energy is lost, it is only converted.• The energy must overcome the friction.• Some kinetic energy is converted to thermal energy

is a result of the friction.

Energy is Conserved within a Closed System

• A closed system is a group of objects that transfer energy only to each other.

• Even though some other energy sources are involved like mechanical (the sum of PE and KE) and sound energy are produced, you end up with the original amount of potential energy.

• Energy is conserved not lost.

Law of Conservation of Energy

• Energy is conserved in all cases, because there no exception to this rule has been found, this rule is described as law.

• The law states energy cannot be created or destroyed, in a closed system.

No Conversions without Thermal Energy

• Any time one form of energy is converted into another, some of its original energy gets converted into thermal energy.

• Perpetual motion is impossible because energy conversions always result in the production of waste thermal energy. (ex. The drinking bird)

• Energy efficient- depends on the ratio of energy input to energy output