Now , measure the length of a bench by means of the span of your hand . Ask your friends to do the same . Did each of you obtain the same measure for that bench ? What could be the reason ?

Take a long rubber band and cut it at one point . At one of its ends tie a clean washed stone or a 50g weight as shown in figure Now hold the other end of the rubber band and make a mark there . Keep the stone hanging in air and measure the length of the rubber band from the stone to the mark made earlier . now take water in a pot and hold the rubber band at such a height that the stone sinks in it . again measure the length of the rubber band up to the mark . : What could be the reason for a shorter length of the rubber band in water ? :

Apparatus: Bars of stainless steel, aluminium and copper, a candle, a burner, pins, etc. : Procedure: Take stainless steel (or iron), copper and aluminium bars, each about 30 cm long and having the same shape. Apply wax spots with the help of candle at a distance of 2 cm from each other on all the three bars. Stick a pin in each of these spots so that it is upright. Now insert the ends of all three bars into a flame at the same time. for a while. What do you see? From which bar do the pins start falling first? Why?

If ten students are asked to measure the length of a piece of cloth up to a mm, using a metre scale, do you think their answers will be identical? Give reasons.

Take a ball of string . Let one student from the class measure four hand spans of the string and cut it there . Let each of the other students in the class cut four hand-spans of the string , too . Now hold all the pieces together by one end . Are they all of the same length ?

Light a candle and stand it upright. Hold your hands on its two sides at some distance from the candle. Bring them closer. : What do you feel?

An 'app' may be available on cell-phones to measure the loudness of sound in decibel. With the help of your teacher, use the app to measure the sound level of a sound from a loudspeaker at some public place. Measure the sound level at different distances from the loudspeaker. Do you observe some relation between the distance from the loudspeaker and sound level?

Answer the following questions:Make two sufficiently long, identical tubes out of a cardboard. Arrange them on a table, in front of a wall as shown in figure . Place a clock near the end of one of the tubes and try to hear the ticking of the clock at the end of the other tube by placing your ear there. Adjust the angles of the two tubes till you can hear the sound very clearly Measure the angle of incidence theta_1 and the angle of reflection theta_2 . Try to see if they are related in any way. In the experiment, what will happen if you lift one of the tubes to some height?

What will you do? Why? Your friend has developed the hobby of snapping selfies.