Motion - Exploration class 9 


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FORCE AND PRESSURE class 8

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FORCE Q.1. Define the term force. What are its characteristics? Ans. In science, a push or a pull on an object is called a force. The fo rce always has a measure of its strength or magnitude and direction in which it is applied. So, Force is a vector quantity. The S.I. unit of Force is N (Newton). Q.2. Forces are due to an Interaction. Justify.  Ans. At least two objects must interact for a force to come into play. This means whenever a force is applied on an object, three things can be easily observed: Ø agent exerting the force Ø the object on which it acts Ø the effect of the force                                                         Q.3.  W...
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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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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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