![Example: Ptolemy[edit]](https://www.universator.com//img/scientific_theory_wikipedia_the_free.jpg)

- The theory of relativity: that the laws of physics are the same for all observers
- The theory of evolution by natural selection: that the observed changes in species occur due to selection of well adapted specimens over less well adapted specimens.
- Big Bang theory: that the universe began as an infinitely small point that underwent expansion to form the universe as we know it today.
Define scientific theory for the students. A good definition could be like, "A scientific theory is a general statement intending to explain nature that is confirmed by all available evidence such that it can be used to predict new, as yet unobserved phenomena." Importantly, a theory is worth very little if it doesn't correctly predict all known evidence. Very importantly, theories are subject to changes as new evidence becomes available. Most theories that you will discuss in a high school science class are well-confirmed and are unlikely to be revised in any significant sense. Theories that are less confirmed are abundant in fields like theoretical physics and cosmology, such as String Theory.
Ask the students if they can think of some more theories in the context of this definition. You will likely have to help.
- The germ theory of illness: that some illnesses are caused by microscopic organisms.
- The heliocentric solar system: that the planets in our solar system orbit around the sun.
- The round Earth theory: that the Earth is round, and not flat, or some other shape.
- The atomic theory of matter: that all matter is made up of atoms.
Ask the students why they don't think of these as theories. Students tend to not think of these as theories because they consider them facts. Indeed, they are facts, but they still fit into the definition of theory because they intend to explain.
5Define a scientific fact. A fact is an objective, verifiable observation. It is the same everywhere. It can be, and has been, verified many times. For example, we know that the germ theory of illness is a fact because we can take bacteria from someone suffering from an illness, look at that bacteria under a microscope, and then inject that bacteria into another individual-who will then get that same illness. We know that the Earth is round because we can travel due west and eventually end up where we started from.
6Ask how a theory can be transformed into a fact. Most theories cannot ever be transformed into fact. No amount of facts supporting such theories makes this so. Remember, a theory is a general statement intended to explain facts. For example, the ancient peoples noticed peculiar points of light that wandered amongst their background. We now know these to be the planets. They wandered because they, like the Earth, were orbiting around the sun, each at different speeds, different distances from the Sun. Nicolaus Copernicus is generally considered to be the first to propose this, and support his theory with hard evidence, but ancient cultures stumbled upon this through speculation. We now consider this a fact because we have sent many craft to these planets and can predict their motions to a very high precision. Of course, our predictions come from the theory (and the laws underlying it).

- Newton's Law of heating and cooling: the change in temperature of two bodies in thermal contact is proportional to their difference in temperature.
- Newton's Laws of motion: statements about how large objects made of atoms behave when moving at low speeds relative to each other.
- The Laws of Thermodynamics: statements about entropy, temperature, and thermal equilibrium.
- Ohm's Law: the voltage across a purely resistive element is equal to the current through the element times its resistance.



