Results

Introduction to cell theory--the idea that 1) all living things are made of one or more cells, 2) cells are the basic unit of life and 3) all cells come from other cells. Explore the roles that Hooke, Leeuwenhoek and others played in developing cell theory.

Hooke and Leeuwenhoek were two of the first scientists to use microscopes to study the microscopic world of cells. Hooke coined the term "cell" after observing the tiny compartments in cork, while Leeuwenhoek discovered a variety of living creatures in pond water, blood, and other samples. They contributed to the cell theory by suggesting that cells are the fundamental units of life and structure, and that all living things consist of one or more cells that originate from other cells by division. 

All living things are made up of cells, which is the smallest unit that can be said to be alive. An organism may consist of one single cell (unicellular) or many different numbers and types of cells (multicellular).

• Determine the variables that affect how charged bodies interact.
• Predict how charged bodies will interact.
• Describe the strength and direction of the electric field around a charged body.
• Use free-body diagrams and vector addition to help explain the interactions.

Introduction to the cell.

Even though molecules, proteins, viruses, and cells are all tiny, there are significant size differences between them. The diameter of a water molecule is roughly 0.28 nanometers. The diameter of the protein hemoglobin is roughly 5 nanometers. The diameter of the HIV virus is roughly 120 nanometers. A red blood cell is 6-8 micrometers.

In this lesson you will learn that:

• Static electricity is a build-up of charge in an object.
• The build-up pf charge is caused by insulating materials rub against each other.
• The motion of these charges causes small shocks, lightening and sparks.
• These charges can be detected. 
• Certain materials can be classified as insulators, and others as conductors.
• Capacitors are small devices in circuits which can store charge.
• Lightning rods are used to allow charges from strikes to travel safely and dissipate in the Earth

Electric charge comes in two varieties, which we call positive and negative. Like charges repel each other, and unlike charges attract each other. Thus, two positive charges repel each other, as do two negative charges. A positive charge and a negative charge attract each other.

How do we know there are two types of electric charge? When various materials are rubbed together in controlled ways, certain combinations of materials always result in a net charge of one type on one material and a net charge of the opposite type on the other material. By convention, we call one type of charge positive and the other type negative.

This short online resource elaborates on the difference between climate and weather and why understanding the climate is important.

This short online tutorial highlights the difference between weather and climate.