Ch#7 : Properties Of Matter Flashcards
Learn about Density , Pressure , Pascal's Law and Young's Modulus. Write down derivations whenever possible
What is Density? Give the Densities of Air , Ice , Water and Platinum.
Definition : Density is defined as the mass per unit volume of a substance
Formula: Density = Mass/Volume
Si Unit : kg/m³
Density of air : 1.3kg/m³
Water : 1000
Ice : 920
State and explain pressure.
Definition : Pressure is defined as the force acting normally per unit area on the surface of a body.
Formula : Pressure = Force/Area
SI Unit : N/m² or Pa
Scalar Quantity
Explain and derive the pressure in liquids.
All Liquids exert pressure. The pressure of a liquid acts in all directions. If we take a pressure sensor and put it in a liquid , we find that pressure varies with depth.
Explanation : Consider a surface of Area A in a liquid at depth h.The length of the liquid cylinder above this surface will be h.The force acting on this surface will be the weight w of the liquid.If ¶ is the density and m is the mass then ,
Derivation :
Mass m = volume X density
Force acting on area A = mg = A h ¶ g
Liquid pressure = ¶gh
Define Pascal’s law and explain the working of a Hydraulic Press.
Definition : The pressure applied at any point of a liquid is transmitted without loss to all other parts of the liquid.
Explanation : Hydraulic Press works on the principles of Pascal’s law. Consider two pistons of cross sectional area a and A.Object to be compressed is places over larger piston A.The force F1 is aplied at piston of area a.The pressure P produced transmits to the large piston and force F2 acts on A.
Derivation :
P = F1/a = F2/A
F2 = F1 X A/
Since A/a > 1 , F2 > F1
State and derive archimedes principle.
Definition : When an object is totally or partially immersed in a liquid , a upthrust acts on it equal to the weight of the liquid displaced by the object.
Explanation : Consider a solid cylinder of area A and and height h immersed in a liquid.Let h1 and h2 be the depths of the top and bottom faces of the cylinder respectively.
h = h2 - h1
If P1 and P2 are the pressures at h1 and h2 respectively and ¶ is the density then
P1 = ¶ g h1 P2 = ¶ g h2
Let F1 be exerted at the cylinder top by P1 and F2 be exerted at the bottom by P2.
F1 = P1 A F2 = P2 A
F1 and F2 are acting on opposite faces of the cylinder. The netforce F will be F2 - F1 in the direction of F2.F is the upthrust.
Upthrust = ¶ g V
How could you find the density of an object with the Archimedes Principle?
Archimedes Principle is useful ti determine the density of an object.The ratio in the weight of a body with an equal volume of liquid is the same as in thier densities.
Density of Object = D
Density of Liquid = ¶
Weight of object = w1
Weight of Equal volume of liquid = w = w1 - w2
W2 is the weight of the sold in the liquid
D/¶ = W1/W
[D = W1/W1 - W2 * ¶]
How do submarines and ships work on the principle of floatation?
Definition : A floating Object displaces fluid having weight equal to the weight of the object.
Application : Ships and Boats are designed on the principle of floatation.A ship would sink if its weight and the weight of its passengers and goods becomes greater than the upthrust of the water.
A submarine can travel over and underwater.It floats over water when the weight of water equal to its volume is greater than its weight. In this state , it is similar to a ship and remains above water level.It has a system of tanks which can be filled with seawater. When the tanks are full , the weight of the submarine increases and its weight becomes greater than the upthrust. It dives and remains underwater. To come back to the surface , air is forced into the tanks to empty them
Define Deforming Force , Elasticity , Stress and Strain.
Deforming Force : It is the applied force which changes the shape , length or volume of a substance.
Elasticity : is the property of a body ti restore to its original size and shape as the deforming force ceases to act.
Stress : It is the deforming force acting on unit area at the surface of a body.
Stress = Force/Area
Si Unit = N/m²
Strain : When stress acts on a body , it changes the length , volume or shape of the body. Comparison of the change causes by stress with the original length , volume or shape is called Strain. If stress produces change in the length of an object then it is called Tensile Strain.
Tensile Strain = change in length/original length
SI Unit : None
State and Explain Hooke’s Law.
Definition : The produced in a body by the stress applied to it is directly proportional to the stress within the elastic limit of the body.
Stress < strain
Stress = Constant X Strain
Stress/Strain = Constant.
Hooke’s law is applicable for all matter within a certain limit. This limit tells the maximun stress that can be safely applied on a body without permanent deformation in its length , volume or shape.It is a limit within which a body restores its original length , volume or shape.When stress crosses this limit , the body is permanently deformed and is unable to restore to its original state.
State and Derive Young’s Modulus. What is the Young’s Modulus of Diamond , Glass and Steel?
Definition : The ratio of stress to tensile strain is called Young’s Modulus.
Explanation : Consider a long bar of length Lo and cross sectional area A.Let an external force F equal to weight w stretch it so its length becomes L. According to Hooke’s law , the ratio of stress and tensile strain is constant
Y = Stress/Tensile Strain
Y = F/A * Lo/∆L
Y = F Lo/A ∆L
Si Unit : N/m²
Steel : 200 x 10⁹ , Glass 60 x 10⁹ , Diamond : 1120 x 10⁹
Y = stress/tensile strain
