Specific Gravity - Definition of Specific Gravity

Specific Gravity - Definition of Specific Gravity The specific gravity of a substance is the ratio of its density to a specified reference substance. This ratio is a pure number, containing no units. If the specific gravity ratio for a given substance is less than 1, that means the material will float in the reference substance. When the specific gravity ratio for a given material is greater than 1, that means the material will sink in the reference substance. This is related to the concept of buoyancy. The iceberg floats in the ocean (as in the picture) because its specific gravity in reference to the water is less than 1. This rising vs. sinking phenomenon is the reason that the term specific gravity is applied, although gravity itself plays no significant role in this process. Even in a substantially different gravitational field, the density relationships would be unchanged. For this reason, it would be far better to apply the term relative density between two substances, but for historical reasons, the term specific gravity has stuck around. Specific Gravity for Fluids For fluids, the reference substance is usually the water, with a density of  1.00 x 103 kg/m3  at 4 degrees Celsius (waters densest temperature), used to determine whether or not the fluid will sink or float in water. In homework, this is usually assumed to be the reference substance when working with liquids. Specific Gravity for Gases For gases, the reference substance is usually normal air at room temperature, which has a density of approximately 1.20 kg/m3. In homework, if the reference substance is not specified for a specific gravity problem, it is usually safe to assume that you are using this as your reference substance. Equations for Specific Gravity The specific gravity (SG) is a ratio of the density of the substance of interest (Ï i) to the density of the reference substance (Ï r). (Note: The Greek symbol rho, Ï , is commonly used to represent density.) That can be determined using the following formula: SG Ï i à · Ï r Ï i / Ï r Now, considering that the density is calculated from mass and volume through the equation Ï  m/V, this means that if you took two substances of the same volume, the SG could be rewritten as a ratio of their individual masses: SG Ï i / Ï rSG mi/V / mr/VSG mi / mr And, since the weight W mg, that leads to a formula written as a ratio of weights: SG mi / mrSG mig / mrgSG Wi / Wr It is important to remember that this equation only works with our earlier assumption that the volume of the two substances is equal, so when we talk about the weights of the two substances in this last equation, it is the weight of equal volumes of the two substances. So if we wanted to find out the specific gravity of ethanol to water, and we know the weight of one gallon of water, then we would need to know the weight of one gallon of ethanol to complete the calculation. Or, alternately, if we knew the specific gravity of ethanol to water, and knew the weight of one gallon of water, we could use this last formula to find the weight of one gallon of ethanol. (And, knowing that, we could use it to find the weight of another volume of ethanol by converting. These are the sorts of tricks that you may well find among homework problems that incorporate these concepts.) Applications of Specific Gravity Specific gravity is a concept that shows up in a variety of industrial applications, particularly as it relates to fluid dynamics. For example, if youve ever taken your car in for service and the mechanic showed you how small plastic balls floated in your transmission fluid, youve seen specific gravity in action. Depending on the specific application in question, those industries may use the concept with a different reference substance than water or air. The earlier assumptions applied only to homework. When you are working on a real project, you should know for sure what your specific gravity is in reference to, and shouldnt have to make assumptions about it.

How to French Interrogative Pronouns Qui and Que

How to French Interrogative Pronouns Qui and Que French has three interrogative pronouns: qui  que, and lequel, which are used to ask questions. They all have differences in meaning and usage. Note that lequel  is a more complicated case and, as such, is addressed separately. Also, while qui and que are also  relative pronouns,  we are only discussing them here in their function as interrogative pronouns. How to Use Qui   Qui  means  who  or  whom; it is used when asking about people. When  who  is the  subject  of the question, you can use either  qui  or  qui est-ce qui. The word order cannot be inverted, and the verb is always third person singular. Qui veut le faire  ? / Qui est-ce qui veut le faire  ?   Who wants to do it?Qui parle  ? / Qui est-ce qui parle  ?   Who is speaking? When whom is the object of the question, qui can be followed by either est-ce que or inversion, as in: Qui est-ce que vous aimez  ? / Qui aimez-vous ?   Whom do you love?Qui est-ce que tu vois  ? / Qui vois-tu  ?   Whom do you see? Qui can also follow a preposition. qui est-ce que tu parles  ? / qui parles-tu  ?   To whom are you speaking?De qui est-ce que tu dà ©pends  ? / De qui dà ©pends-tu  ?   Upon whom do you depend? How to Use Que Que means what and is used to refer to ideas or things. When  what  is the subject of the question, you must use  quest-ce qui  followed by a verb in the third person singular, with no inversion. Quest-ce qui se passe  ?   Whats happening?Quest-ce qui est tombà © sur la terre  ?   What fell on the ground? When what is the object of the question, it can be followed by est-ce que or inversion. Quest-ce quil veut  ? / Que veut-il  ?   What does he want?Quest-ce que tu penses de mon idà ©e  ? / Que penses-tu de mon idà ©e  ?   What do you think of my idea?Quest-ce que cest (que cela)  ?   What is that? Que to Quoi After a preposition, que changes to quoi. De quoi est-ce que vous parlez  ? / De quoi parlez-vous ?   What are you talking about? quoi est-ce quil travaille  ? / quoi travaille-t-il  ?   Whats he working on? More Examples of the Interrogative  Qui and Que Qui donc ta frappà ©Ã‚  ?   Who hit you? Qui est-ce qui en veut  ?   Who wants some ? Qui cherchez-vous  ?   Who are you looking for? Cest qui  ?  Ã‚  Whose is it,  to whom does it belong? qui le tour  ?   Whose turn (is it) ? De qui parles-tu  ?   Who  (ou  whom) are you talking about? Qui est-ce que tu connais ici  ?   Who do you know around here? qui est-ce que je dois de largent  ?   Who do I owe money to ?,  to whom do I owe money?  (soutenu) Quy a-t-il  ?   Whats the matter ? Que devient-elle  ?   Whats become of her? Quest-ce que je vois / jentends  ? What is this I see / hear ? Quest-ce qui tarrive  ?   Whats the matter with you? Quest-ce que la libertà ©Ã‚  ?   What is freedom? Summary of French Interrogative Pronouns Subject of question Object of question After preposition People quiqui est-ce qui quiqui est-ce que qui Things quest-ce qui quequest-ce que quoi