Motion - Exploration class 9 


New NCERT 

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Friction (part-3)

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FRICTION Q.6. What is spring balance? How does it work? Ans.  Spring balance is a device used for measuring the force acting on an object. It consists of a coiled spring which gets stretched when a force is applied to it. Stretching of the spring is measured by a pointer moving on a graduated scale. The reading on the scale gives the magnitude of the force.                                                    Q.7. What are static, sliding and rolling friction? Ans. The force required to overcome friction at the instant an object starts moving from rest is a measure of static friction . The force required to keep the object moving with the same speed is a measure of sliding friction . When a surface rolls over another, the friction which slows down the motion of rolling object is called rolling friction .     ...
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Sound (part -3) class 8

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                                                                                                   SOUND Q.6.  Draw a well labeled diagram of human ear and explain its functioning? Ans. A human ear is divided into 3 parts: 1. Outer Ear : It is the only part of the ear that is visible to us. It consists of Pinna, Ear Canal and Ear Drum. The Pinna collects the sound waves and directs them to the ear canal. At the end of ear canal, there is ear drum which is slightly stretched membrane. When the vibrations strike the ear drum, it starts vibrating and transmits the sound to the middle ear. 2. Middle Ear : The middle ear is a cavity with three tiny important ear bones. These bones are M...
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Sound (part -4) class 8

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  SOUND Characteristics of sound Q.8. Define the following terms: Frequency, time-period and amplitude. Ans. Frequency : The number of oscillations per second is called the frequency of oscillation. Frequency is expressed in hertz. Its symbol is Hz. Time-period : The time period is  the time taken by the oscillating object to complete oscillation. It is expressed in seconds.   Amplitude : the amount of maximum displacement of vibrating particles of the medium from their mean position is called the Amplitude of oscillation. It is also known as size of vibration. The SI unit of amplitude is  the meter. Q.9. A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency. Q.10. The sound from a mosquito is produced when it vibrates its wings at an average rate of 500 vibrations per second. What is the time period of the vibration? Q .11. How c an we differentiate sounds on the basis of their am...
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