Burette

Burette

A burette is a vertical cylindrical piece of laboratory glassware with a volumetric graduation on its full length and a precision tap, or stopcock, on the bottom. It is used to dispense known amounts of a liquid reagent in experiments for which such precision is necessary, such as a titration experiment(a common laboratory method of quantitive chemical analysis that is used to determine the unknown concentration of a known reactant).Burettes measure from the top since they are used to measure liquids dispensed out the bottom. The difference between starting and final volume is the amount dispensed

Pipette

Pipette

Pipettes are commonly used in molecular biology as well as medical tests. Pipettes come in several designs for various purposes with differing levels of accuracy and precision, from single piece glass pipettes to more complex adjustable or electronic pipettes. Many pipettes types work by creating a partial vacuum above the liquid-holding chamber and selectively releasing this vacuum to draw up and dispense.

Measuring Cylinders

Measuring Cylinder

A measuring cylinder, also known as a graduated cylinder is a piece of laboratory equipment used to accurately measure the volume of an object. Water displacement can be used to find out the volume of an object. Measuring cylinders are generally more accurate and precise for this purpose than flasks and beakers.

Surface Tension

Surface tension is a property of the surface of a liquid. It is what causes the surface portion of liquid to be attracted to another surface, such as that of another portion of liquid. Surface tension is caused by cohesion (the attraction of molecules to like molecules). Since the molecules on the surface of the liquid are not surrounded by like molecules on all sides, they are more attracted to their neighbors on the surface.

Examples of Surface Tension

Water beading on a leaf

• Beading of rain water on the surface of a waxed automobile. Water adheres weakly to wax and strongly to itself, so water clusters into drops. Surface tension gives them their near-spherical shape, because a sphere has the smallest possible surface area to volume ratio.

Source:http://en.wikipedia.org/wiki/Surface_tension

Why is yawning contagious?

Why is yawning contagious?

Today we know that a yawn is a reflex of inhalation and exhalation that draws more oxygen into the bloodstream. A reflex is a built-in physical reaction that people often do not have control over. A yawn is often associated with a person being tired, but this is not always the cause for a yawn. People yawn for many reasons including stress, boredom, emotion and over-work.

If one person yawns, this appears to cause another person to yawn. Researchers have found that 40-60% of people who see a picture of someone yawning will yawn themselves. Even reading the word YAWN can make people yawn.

Although this “contagious” yawning behavior is not understood, it has been suggested that this could be the result of an unconscious herding behavior — a subtle way to communicate group behavior, such as when a birds follow the behavior of one bird, and all rise together as a whole flock.

Maybe a yawn is a signal to the group that it’s time to go to sleep. Or if someone yawns when they’re bored, it may be a sign to change the topic of conversation. Yawning is not limited to humans. Animals of all types yawn.

Some of the more scientific explanations of why we yawn are caused by physical needs. One likely explanation is that the yawning reflex is triggered when our blood needs more oxygen. The deep breath helps replenish the levels of oxygen in our blood. Another common theory is that the yawn help regulate our body temperature. Other hypotheses suggest that the same chemicals in our brain that affect our moods and emotions cause us to yawn.

Source:http://www.chevroncars.com/learn/wondrous-world/yawn-contagious