Notes: Ch. 6 Energy and Power

What is energy? The ability to do work or cause change is called energy. Work can be thought of as the transfer of energy.

Kinetic Energy The energy of motion is called kinetic energy. The kinetic energy of an object depends on both its mass and its velocity. Kinetic energy increases as mass increases. Kinetic energy increases as velocity increases.

Potential Energy Energy that is stored or held in readiness is called potential energy. Ex. Food a boulder at the top of a mountain

Elastic Potential Energy The potential energy associated with objects that can be stretched or compressed is called elastic potential energy. Ex. a stretched rubber band A squished spring

Gravitational Potential Energy Potential energy that depends on height is gravitational potential energy. Ex. a book on a desk

Different Forms of Energy Mechanical energy is the energy associated with the motion or position of an object. Ex. a frog leaping a car moving

Different Forms of Energy Thermal energy is a measure of the energy of the particles in an object. Ex. ice cream melting

Different Forms of Energy Chemical energy is potential energy stored in chemical bonds that hold compounds together. Ex. the food you eat Gasoline

Different Forms of Energy Electrical energy is energy associated with moving electric charges. Ex. power in power lines

Different Forms of Energy Electromagnetic Energy is a form of radiant energy, which travels in waves. Ex. visible light Microwaves Infrared radiation Ultraviolet radiation

Nuclear energy is stored in the nucleus of an atom and is released during reactions. Ex. nuclear power in a power plant The sun and other stars

Conversions Between Forms of Energy A change from one form of energy to another is called an energy conversion. Most forms of energy can be converted into any other form. ex. a toaster converts electrical energy into thermal energy

Kinetic and Potential Energy One of the most common conversions is from kinetic to potential energy and back. Ex. Energy Conversion in an Earthquake Ex. Energy Conversion in a Waterfall Ex. Energy Conversion in a Pole Vault Ex. Energy Conversion in a Pendulum

Conservation of Energy According to the law of conservation of energy, energy cannot be created or destroyed. So what happens to the energy in a pendulum? Why does it slow down? The mechanical energy of the moving pendulum is transformed into heat energy due to friction. So, it is not lost, but converted.

A little change…. Einstein changed the law of conservation of energy with his theory of relativity. He said that energy can sometimes be created, but in order to do so, matter must be destroyed. Therefore, scientists say that energy and matter together are always conserved.

Conserving Energy Conserving energy means saving it, or not wasting it. Ex. Not wasting fossil fuels.

Photosynthesis The process through which plants make food is known as photosynthesis. Photo = “light” Synthesis = “putting together” During photosynthesis, white light (electromagnetic energy) is converted into food (chemical energy).

The Nature of Light The sun is the source of energy on Earth. There are three things that can happen to light. It can be: Transmitted (allowed to pass through) Reflected (bounced off) Absorbed (taken in)

Plants and Light Plants absorb some colors of the visible spectrum and reflect others. They have pigments that absorb different colors of light. The colors that are not absorbed (green) are reflected. This is why plants usually appear green. Chlorophyll is the pigment that gives plants their green color. It absorbs most blue and red light, and reflects the green part of the spectrum.

Energy Conversions in Photosynthesis Photosynthesis is the process through which plants convert the radiant energy of the sun into chemical energy. Capturing the Sun’s Energy Photosynthesis begins when chlorophyll and other pigments capture the sun’s radiant energy.

Using Energy to Make Food Water and Carbon dioxide are combined with the radiant energy to create a sugar that the plant uses for food. The chemical formula for this is……

Light energy carbon dioxide + water → glucose + oxygen 6CO 2 6H 2 OC 6 H 12 O 6 + O 2

Glucose and Stored Energy The breakdown of glucose in a plant, is called respiration. This is when the chemical energy is released. It is similar to digestion in humans.

Fossil Fuels A fuel is a material that releases energy when it burns. A fossil fuel is an energy-rich substance formed from the remains of organisms. This energy was stored as potential energy when the plants of that time converted the sun’s radiant energy into chemical energy.

Using Fossil Fuels The process of burning fuels is known as combustion. Today in coal burning power plants, coal is burned to heat water, which creates steam that runs turbines. These turbines are connected to generators which produce electricity.

The energy conversions look like this: Chemical energy → thermal → mechanical → electrical

Fossil Fuels