# Investigatory Project in Physics

PROJECT 1 : THE DAMPED OSCILLATIONS

Aim:

Study of damping of a bar pendulum by fixing card board pieces of different sizes at its bottom

Materials and Apparatus:

(1) A metre scale as compound bar pendulum

(2) Card board discs (square, rectangular or circular discs) of different size

(3) Stop-watch, stand etc

Procedure:

A small hole is drilled near one of the end of the metre scale. A long needle is passed through the hole. The size of the needle should be such that the scale should oscillate freely about the needle. The needle is firmly clamped horizontally on a suitable stand. It is kept near the edge of a table so that the metre scale can oscillate infront of the edge. A card board disc of area ‘a’ is cut off. It is fixed near the bottom of the metre scale in such a way that when the scale oscillates, the plane of the disc is perpendicular to the direction of oscillation.

The equilibrium position of the scale is marked on the edge of the table. A small amplitude of oscillation is also marked. The bar pendulum is pulled upto this mark and released. Simultaneously the stop watch is started. When the pendulum comes to rest, the total time ‘t’ of oscillations is noted. The experiment is repeated a number of times and the average value of ‘t’ is taken. The experiment is repeated for card board discs of different area a keeping their centre of mass at the same position on the scale. A graph is drawn with the time ‘t’ of oscillation and the area ‘a’ of the discs.

PROJECT 2 : THE INERTIAL BALANCE

Aim:

To construct an inertial balance, calibrate and find the inertial mass of a body.

Material required:

(1) A hacksaw blade of length 30 to 50 cm

(2) A light scale pan

(3) A set of known weights and the body of unknown mass

(4) Stopwatch, knitting needle

Procedure:

The hacksaw blade is clamped horizontally with its flat sin lace vertically over table. A knitting needle is kept vertically infront of the free end of the blade. A scale pan of negligible weight is glued at the flat surface of the hack-saw blade near the free end.

A suitable mass m, say 20 g, is placed in the pan. The end of the hacksaw blade is displaced horizontally and released. The blade vibrates horizontally. So the acceleration due to gravity does not affect the oscillations. The period of oscillation T is determined. The experiment is repeated with mass 2m, 3m, ... in the pan.

T = 2π(m/k), where k is the force constant of the blade.

T2/m = a constant

A graph is drawn with T2 along the Y-axis and m along the X-axis. This is the calibration curve.

The body of unknown mass ‘x’ is placed in the pan and the period of oscillation ‘T' is determined. The inertial mass x of the body is noted from the graph. (The mass in should be selected depending on the length, width and thickness of the hacksaw blade so that the period may be determined accurately)

To find m and T2

PROJECT 3 : THE HELICAL SPRING

Aim:

To study the variation of spring constant k with its diameter by making helical springs of different diameters using thick copper or steel wire.

Materials and apparatus

(i) Thick copper or steel wire

(ii) Stand

(iii) Stopwatch

(iv) Weight hanger and slotted weights

(v) Cylindrical tubes of different diameters

Procedure

Helical springs of different diameters are made by winding the copper wire over cylindrical tubes of different diameters. The diameter D of the spring is determined by measuring the diameter of the tube using a vernier calipers. The spring constant k is determined by load - extension method. The reading are tabulated. A graph is drawn connecting k and D.

PROJECT 4 : THE CLEANSING EFFECT OF DETERGENT

Aim:

To study the comparative cleansing effect of different detergents by the study of capillary rise

Materials and apparatus:

(1) A capillary tube of uniform bore

(2) Beaker

(3) Stand

(4) Common balance

(5) Different detergents

(6) One holed cork

(7) Divider, scale etc

Theory

For a give capillary tube, the capillary rise of liquid in the tube is directly proportional to the surface tension of the liquid. The presence of the detergent in water reduces surface tension. For equally concentrated solution of different detergent in water, capillary rise is Minimum for the best detergent and maximum lot worst detergent.

Procedure

Equal masses of different detergents are taken by finding the mass of the detergent using physical balance. Equal volumes of distilled water are taken in different beakers. The detergents are dissolved in water. Thus different beakers contain different detergents having the same concentration. The beakers are labelled as A, B, C,…..

The capillary tube is cleaned first with an acid, then with an alkali and finally with water. It is then passed through a hole in a cork and is arranged vertically by suitable stand with its lower end dipping in the solution contained in the beaker marked A. The solution rises in the capillary tube up to certain height. Using a divider and a metre scale, the height h of the solution in the tube from the surface of the solution in the beaker is measured. The experiment is repeated with the other solutions also. The capillary tube should be thoroughly cleaned and rinsed in distilled water before dipping in fresh detergent solutions.

Observation

Result

The different detergents in the order of cleaning power are as follows.

(1)..... (2)..... (3)..... (4).....

PROJECT 5 : THE COEFFICIENT OF FRICTION

Aim:

To find the relationship between forces of static friction and normal reaction by plotting a suitable graph and to find the coefficient of friction between a wooden block and horizontal surface

Materials and Apparatus

A wooden block, a smooth frictionless pulley, a table with a smooth horizontal top surface, scale pan, weight box, string etc

Procedure

The weight of the wooden block and that of the scale pan are determined using a spring balance. One end of a light inextensible string is tied to the hook fixed to the wooden block. The other end of the string passes over the pulley and carries the scale pan which hangs freely in air. Ensure that the string between the block and the pulley is horizontal.

Some weights are placed in the scale pan. The weight in scale pan is so adjusted that on gently tapping the table, the wooden block just begins to slide. The weight of the scale pan together with the weight in the pan gives the force of limiting friction Fms. The normal reaction R is given by the weight W of the wooden block. The coefficient of static friction is calculated by the equation,

µ = Fms/W

A known weight P is placed on the wooden block. Now the normal reaction R becomes (W + P). The limiting friction Fms, is determined as explained above. The co-efficient of static friction is calculated by the equation,

µ = Fms /(W + P)

The experiment is repeated for different weights on the block. The mean value of coefficient of friction µ is calculated. A graph is drawn with limiting friction Fms along the y-axis and normal reaction R along the x-axis. The graph is a straight line. The slope of line is a measure of the coefficient of friction between the surfaces of the block and the table.

Observation

Weight of the block = W = ……g

Weight of the scale pan = w = ……g

Results

(i) The graph connecting limiting friction and the normal reaction is a straight line.

(ii) Coefficient of static friction µ between the block and the table

(a) by calculation, µ = ….

(b) from the graph µ = ….

Note: Effect of lubricants on friction can be studied by performing the above experiment with lubricant between the surface of the block and the table in contact.