Unit 1 Physics On The Go Notes 1s4xh

Unit 1 physics on the go Physical quantities It is a quantity that can be measured. All physical quantities can be expressed with a magnitude and a unit. Without the correct unit any physical quantity is meaningless. Physical quatities split into two that is basic and derived Basic quantities There are six basic quantities. These quantities cannot be measured using any other quantity. Below is the list of basic quantities. Mass, length, time, temperature, electric current and amount of substance Derived qunatities These are physical quantities derived out from basic quantities Homogenous equation The SI base units of each term of the equation are same those equations are said to be homogenous equations Experimental physics for unit 3b Accuracy: getting all the readings correct Precision: means getting all the readings close together A good experimenter will have high precision but if his instruments are not good it will lead in poor accuracy this leads to systemetic error, this is the error due to intruments. A poor experimenter will have less precision and the reading will be scattered resulting random errors, this the error due to experimenter or human error. Systemetic errors can be minimised by taking sensible precautions, such as checking for zero erros, avoiding parallax errors and by drawing suitable graphs. Random errors can be minimised by taking a number of repeated readings and taking the average and by drawing a graph that in effect averages the number of values Uncertainity Metre rule: 1mm Vernier calliper: 0.1mm Micrometer screw guage: 0.01mm

%uncertainity = For multiple readings %uncertainity =

Micrometer screw guage Reading = Main scale + (rotating scale x 0.01) reading will be on mm. To check for zero error the studs anvil and spindle with no object in between. If the zero of rotating scale coincides with mainscale then instrument do not have zero error. If the zero on the rotating scale lies above the mainscale then the zero error have to be added to the reading and if the the zero on the rotating scale lies below the mainscale then the zero error have to be subtracted. Vernier calliper Reading = Main scale + (vernier scale x 0.01) Reading will be on cm To check for zero error the sections A and B if zeros in both scale coincides then it has no zero error. If vernier scale zero is more to right then the zero error have to be subtracted. If vernier scale zero is more to left then the zero error have to be added to the reading. Percentage difference 1) %Difference = 2) %Difference = This is used to confirm relationships, to check whether the materials are made of same or not, or to check whether the readings are accurate or not compared with the standard value If % difference is less than total % uncertainity then both are made of same material or relationship is confirmed If total % uncertainity is not given then compare % difference with 10% Mechanics Scalar quantity: physical quantity that has only magnitude Vector quantity: physical quantity that have both magnitude and direction. Rectilinear motion Distance: length of the path travelled by and object Displacement: shortest distance between two points in a specific direction Speed: Distance travelled in unit time Average Speed: Total distance travelled over total time taken Velocity: rate of change of displacement Uniform velocity: equal displacement in equal intervals of time Instantaneous velocity: velocity at a particular instant Acceleration: rate of change of velocity Uniform acceleration: equal change in velocity in equal intervals of time

Motion graphs Displacement time graphs: gradient gives velocity Velocity time graphs: gradient gives acceleration, area under graph gives displacement Acceleration time graphs: acceleration patterns can be read from it Equations of motion v = u+at These equations are only applicable if the acceleration s = (u+v) t is uniform s = ut + ½ at2 v2 = u2 + 2as Free Fall Falling under the influence of gravitational force only and no other forces like air resistance acts on it. Projectile motion already covered in M1 Forces A force is a push or a pull exerted on an object. There are two types of forces forces and non forces. forces include friction, normal reaction etc. non forces include gravitational force, magnetic force and nuclear force. Equilibrium: when number of forces act on a body and the vector sum of all these forces add up to zero then the object is said to be in equilibrium. If object is in equilibrium then the line of action of all the forces acting on the object will through one point. Newton’s first law of motion An object will remain in a state of rest or continue to move with a constant velocity unless acted upon by a resultant external force Newton’s second law of motion Acceleration of a body of constant mass is directly proportional to the resultant force applied to it and it acts in the direction of the resultant force. Newton’s third law of motion If body A exerts a force on body B, body B will exert an equal and opposite force on body A. Newton’s third law pairs must always     

Act on two separate bodies Be of the same type Act along the same line Be equal in magnitude Act in opposite directions

Energy and Power Work: it is the product of force and distance moved in the direction of force W = F x s

Power: rate of work done in unit time P =

or P = F x v

Energy: the ability to do work Potential energy: the energy present in an object due to its position E p = mgh Kinetic energy: the energy present in an object due to its motion or vibration E k = ½ mv2 Law of conservation of energy Energy can never be created nor destroyed but it can be transformed from one form to the other. In short total energy of the system is constant Fluid dynamics A substance which can flow is known as a fluid. All liquids and gases are fluids Floatation: when up thrust is exactly equal to the weight of the object. Viscosity: it is the nature of the fluid which offers resistance to flow.  P = in case of fluids P = gh Up thrust is the force that helps object to float in water. The pressure of the liquid causes force at the top and bottom of the object So U = F2 – F1 Up thrust equals weight of fluid the object displaces Derivation U = F 2 – F1 F1 = P1 A = gh1A U = gA (h2h1) If height is known then area becomes volume So U = Vg =mg Note V is mass of fluid

F2 = P2 A = gh2A

Sinking An object will sink in a fluid if it’s up thrust is less than its weight, so the resultant would act downwards resulting it to accelerate downwards.

Stokes law Viscous drag experienced by a spherical object is directly proportional to the radius (r), velocity (v) and coefficient of viscosity (n) F  nrv Terminal velocity is the constant maximum of object through fluid. At terminal velocity W = U+F For spherical object

v=

(s - f)

Unit of coefficient of viscosity is Pas Stream line: represents the velocity of a fluid at each point within it. Laminar flow Flow lines are parallel to each other, velocity at a point on a stream line is equal. No eddies vortices formed Turbulent flow Eddies and vortices whirl pools formed. Velocities varies lines cross over each other no definite stream lines

Strength of materials Hooke’s law Extension is directly proportional to the force applied within the proportionality limit. Proportionality limit: this is the point up to which the material obeys Hooke’s law. In this region extension is directly proportional to force Elastic limit: it is the maximum force at which the material regains original shape when the force is removed. Yield point: the point at which material behavior changes from elastic to plastic, for a given force a large extension is produced beyond this point. So the material deforms permanently. Breaking point: the point at which the material breaks is known as the breaking point this point always occurs beyond elastic limit. Elastic deformation: A material undergoing elastic deformation will return to its original dimensions when the deforming force is removed. Plastic deformation: A material undergoing plastic deformation will remain deformed when the deforming force is removed and it will not gain its original dimensions. Properties of solid materials Hardness: the harder the material the more difficult it is to indent or scratch the material Stiffness: A stiff material will have a high Young’s Modulus Toughness: a tough material is able to absorb energy from impacts or shocks without breaking. Tough materials are able to undergo considerable plastic deformation. A tough material has a large area under stress strain graph that is energy stored per unit volume by the material Brittleness: brittle material will shatter or crack when subjected to large forces. A brittle material undergo no or very little plastic deformation before breaking Ultimate tensile strength: this is the strength of the material. It is the maximum stress it can withstand before breaking. Malleability: ability of material which can be hammered out into thin sheets. Shows large plastic deformation in stress strain graph Ductile: ability of material which can be drawn into thin wires. Shows large plastic deformation in stress strain graph Hooke’s Law applications F=kx

E=

W= ½ kx

E/V = ½ 

W= ½ kx2 Macroscopic level

Microscopic level

Elastic deformation Shows change in shape when the force is applied regains its original dimension when force is removed When force is experienced distance between atoms increases so the bonds between atoms is stretched without breaking once the force is removed atoms come to original position

Plastic deformation Material produces permanent extension. Remains deformed even when force is removed Distance between atoms increases and the bonds between them are broken, when force is removed atoms cannot gain its initial position.

Note: Difference between stress strain graph and force extension graph The stress strain graph represents properties of the material, which means the stress strain graph for a material is always the same. Whereas the force extension graphs depends on the dimensions of the sample used. Hysteresis Rubber absorbs energy during each cycle of loading and unloading this is known as hysteresis.

    

The arrows indicating loading and unloading of the rubber band. Area under the loading curve indicates work done per unit volume on the band. Area under the unloading curve indicates work done per unit volume by the band as it relaxes. The shaded region is the Hysteresis loop. The Hysteresis loop for stress strain graph indicates the energy per unit volume transferred to internal energy for each cycle.

MICROSCOPIC EXPLANATION FOR RUBBER In rubber molecular chains are coiled up. When rubber is stretched molecular chains straighten up. When it is relaxed molecular chains recoil backs to original length, but the manner by which it does this is very different to a metal. This shows that energy is absorbed during each cycle which is dissipated in the form of heat. When rubber band is repeatedly stretched and relaxed in a short time, it will become warm. The rubber with small hysteresis loop is more resilient and is used in car tires The rubber with large hysteresis loop is less resilient and is used in shock absorbers