Category Forces of Nature

Bats cannot see very well. To orient themselves during their night flights, they emit ultrasounds. We cannot hear these sounds. The ultrasonic waves falling on obstacles or preys get ‘reflected’ back and reach the sensitive ears of bats. Thus, they come to know what all is present around them and where their prey is. This concept is also used in shipping to determine the depth of the sea using a device called sonar. It comprises a sound transmitter, a receiver, and a clock. The time difference between sending and receiving sound waves is measured, which is used to calculate the depth of the sea. 

If you call out your name in the direction of a vertical, bare rocky wall, you will hear it again after some time. An echo comes because the sound waves are reflected back from the wall. When sound is produced in enclosed spaces, such as churches and gymnasiums, multiple reflections build up and blend together. This phenomenon is known as reverberation. 

Ultrasonic waves are those sound waves that are inaudible to our ears because they have a very high frequency. These energy-rich waves are used in many ways such as cleaning dental braces or spectacle glasses. Ultrasonic waves excite the liquid to vibrate so fast that it removes the dirt. Ultrasonic waves are also reflected from the inner organs of our body; thus, an echo is produced. This echo can be recorded and displayed by medical devices. In this way, doctors can safely monitor the development of a foetus inside the mother’s womb. 

As the police car approaches us, the pitch increases, and when it moves away from us, the pitch decreases. When the car approaches us, the sound waves of the siren are ‘compressed’ more towards us, resulting in higher pitch. When the car is moving away, the sound waves get stretched; as a result sound fades away. This effect can be noticed only by an outside observer; the driver hears the same pitch of sound at all times. This phenomenon is called the Doppler effect, which is named after its discoverer.

Jets that fly faster than sound compress the air at the front. This forms a head wave. After a certain point of time, the pressure of the air gets discharged like an explosion. As a result, a loud bang takes place and we hear a loud sound. However, ultrasonic sounds are not audible to us. Bats and other animals use ultrasonic waves for orientation. Sound always propagates in the form of waves. Because of this reason we notice a change in the pitch of the siren of the vehicle passing us.

There are two types of sensory cells present on our retina: rods and cones. At twilight more than 100 million rods permit us to distinguish between the colourless bright light and the dark. During the day around 6 million cones help us see a variety of colours. The eyes of dogs possess very few cones, which are sensitive only to blue and yellow. For this reason, dogs see the world differently from us. Even there are many people who are blind to red and green and cannot correctly distinguish between these two colours.