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Main topics covered in this part of CBSE  Science, Sound: Chapter Notes, are: Sound-Production and Propagation Medium Wave and its Types Characteristics of Sound Audible Frequency Reflection of Sound and its Laws Applications of Reflection of Sound Key notes for Chapter - Sound, are: Sound Sound is a form of energy which produces a sensation of hearing in our ears. Production of Sound  Sound is produced due to the vibration of objects.  Vibration is a periodic back-and-forth motion of the particles of an elastic body or mediumkind about a central position. It is also named as oscillation.  For example: Stretched strings of a guitar vibrate to produce sound. When membrane of a table is struck, it vibrates to produce sound. Propagation of Sound The travelling of sound is called propagation of sound. Sound is propagated by the to and fro motion of particles of the medium. When an object vibrates, the particles around the medium vibr...

Friction  is a force that opposes motion between any surfaces that are touching. Friction can work for or against us. For example, putting sand on an icy sidewalk increases friction so you are less likely to slip. On the other hand, too much friction between moving parts in a car engine can cause the parts to wear out. Other examples of friction are illustrated in the two  Figures  below Friction between the graphite in a pencil and a sheet of paper leaves a mark on the paper. Friction between a bicycle brake pad and the rim of a wheel causes the wheel to stop turning. Did you ever rub your hands together to warm them up, Why does this make your hands warmer? The answer is friction. Why Friction Occurs Friction occurs because no surface is perfectly smooth. Even surfaces that look smooth to the unaided eye make look rough or bumpy when viewed under a microscope. Look at the metal surfaces in the  Figure  below. The aluminum foil is ...

FORCE AND PRESSURE Force Force plays a great role in our life as it is helpful in doing any work. Like in playing cricket and basketball. We need force to play. Force is defined as a push or a pull or we can say force is a physical quantity that can change the speed, state, direction and dimension of an object. For example, when we put the force on the door it opens. The changes that force can bring are written as follows: Change in speed If someone pushes your bicycle, it starts moving faster. In this case, the force that we apply on the bicycle changes the speed of the bicycle. Speed can be increased or decreased also. Note: Force comes into play when at least two bodies interact. Or we can say that two bodies are necessary to put force comes into play. Change in state of body In this case, the body which is at rest can be put into motion or the body in motion goes in rest. For example: If a football placed on the ground is at rest...