Seals and sea lions are pinnipeds, an order of partially aquatic, flipper-footed, carnivorous mammals that also includes walruses.

Sea lion balancing a soccer ball. Image courtesy of The Huffington Post.

Essortment.com on seal v. sea lion

A calendar is a system for dividing and arranging time into periods of days, weeks, months, and years. It also refers to a table displaying these divisions used to keep track of events, such as holidays and appointments.

A calender is a set of pressure rollers through which paper or fabric is passed to make it smooth and glossy.

A clip is a device that holds multiple cartridges together to facilitate loading rounds into the magazine of a firearm. Common designs include en-bloc, stripper, and moon clips.

A magazine is a container with a spring mechanism used to store and load rounds into the chamber of a repeating firearm. Magazines may be internal or detachable, and are often shaped like a box, drum, or tube.

A clip fits inside a magazine, lacks a spring-loaded feed mechanism, and is never fixed to the weapon.

The Gun Zone on clip v. magazine

Bryce70’s clip v. magazine video

A principle is a fundamental truth, doctrine, rule of conduct, natural phenomenon, or quality.

As an adjective, principal means first, chief, or foremost. As a noun, a principal is:

• the head of a school
• a person with a leading or starring role
• the original amount of a debt, on which interest is calculated
• a person who empowers an agent to act as a representative
• someone directly responsible for committing a crime
• the main body of an estate, as distinguished from its interest or revenue

Grammar Girl on principle v. principal

Refraction

When a wave (of light, sound, water, etc.) passes from one medium (e.g., glass or air) into another, its speed will change. If the wave hits the boundary between the substances at an oblique angle, the change in speed will cause it to bend. This phenomenon is called refraction, and is described by Snell’s law. Waves bend toward the normal when they slow down, and away from the normal when they speed up.

Refraction is a key principle used in the manufacture of lenses for eyeglasses, telescopes, and cameras. It is also responsible for mirages, rainbows, and the perceived bending of straws in drinks.

Ordinary (left) and negative refraction (right). Image courtesy of Nature.com.

Diffraction

Diffraction occurs when waves bend around obstacles or spread out after passing through aperatures. This effect is most pronounced when the scale of the obstacle is about the same as the wavelength of the waves. If the wavefront passes through several closely-spaced openings, an interference pattern of light and dark regions will form.

Diffraction causes the edges of shadows to blur, and allows sound to travel around objects. The iridescent colors observed on peacock feathers, sea shells, and CDs are caused by these materials acting as diffraction gratings.

Astronomy 162 on refraction v. diffraction