CHAPTER 5 SOUND
Sound is produced by vibrating objects. When an object vibrates, the particles around the object start vibrating. This disturbance travels in the medium and sound reaches the ear. This is called a sound wave. A wave is a disturbance that moves through a medium when the particles are set in motion.
Sound needs a medium to travel as it is a mechanical wave. It travels as successive compressions and rarefactions in the medium.
Sound waves are a longitudinal wave, which means that the particles move parallel to the direction of propagation.
CHARACTERISTICS OF A SOUND WAVE
Time period (T): The time taken by the wave to complete one oscillation is called time period.
Frequency (): The number of oscillations per unit time is called the frequency. ν= 1/T
Wavelength (λ): The distance between two consecutive compressions or two rarefactions is called the wavelength.
Speed (v) = νλ
REFLECTION OF SOUND
The incident sound and the reflected sound make equal angles with the normal to the reflecting surface and the three lie in the same plane.
An echo is the reflected sound that can be heard a little later than the original sound. To hear a distinct echo, the time interval between the original sound and the reflected sound must be 0.1 second and the minimum distance of the obstacle from the sound source must be 17.2 metres.
Reverberation: The repeated reflection which results in persistence of sound is called reverberation.
Intensity: the amount of sound energy passing each second through a unit area is called the intensity of sound.
The audible range of hearing for humans is 20 Hz- 20 kHz.
Infrasonic: The sound waves with frequencies below the audible range are called infrasonic.
Ultrasonic: The sound waves with frequencies above the audible range are called ultrasonic.
APPLCATIONS OF ULTRASOUND
CHAPTER 4 WORK AND ENERGY
Work done on an object is the magnitude of the force multiplied by the distance moved by the object in the direction of the applied force.
The unit of work is joule.
1 joule= 1 newton x 1 metre
If the force does not bring about any displacement in the object, the work done is considered to be zero.
Energy is the capability to do work.
An object in motion has kinetic energy. For an object with mass m moving with velocity v,
K.E= 0.5 mv2
The energy possessed by a body due to its change in position or shape is called potential energy. The gravitational potential energy of an object of mass m, at a height h is given by mgh.
Law of conservation of energy: This law states that energy can neither be created nor destroyed. It can only be transformed from one form to another.
The sum of the kinetic and potential energy of an object is called its mechanical energy.
Power is the rate of doing work. Its SI unit is watt. 1 W = 1 J/s
The energy used in one hour at the rate of 1kW is called 1 kWh.
CHAPTER 3 GRAVITATION
All objects in the world attract each other. This force of attraction is called gravitational force.
The formula for gravitational force experienced by two bodies is:
F= G (M x m)/d^2
The acceleration during a free fall due to the gravitational force of the earth is called acceleration due to gravity. It is denoted using ‘g’. Its value is taken to be 9.8 m s-2.
The force of gravity decreases with altitude. It also varies on the surface of the earth i.e. it decreases from poles to the equator.
The weight of a body is the force with which the earth attracts it which is equal to the product of the mass and the acceleration due to gravity.
When a body is immersed in a liquid, it experiences buoyancy. If an object has less density than that of the liquid, it floats on the surface of the liquid. However, if the object is denser than the liquid, it sinks.
CHAPTER 2 FORCE AND LAWS OF MOTION
An unbalanced force is required to set an object in motion.
LAWS OF MOTION
There are three laws of motion:
Mathematical formulation of the law gives:
F=ma, where m=mass, a= acceleration and F=Force
Momentum (p): It is the product of its mass and velocity i.e. p=mv
In an isolated system, the total momentum remains conserved. This implies that during collision: m1u1 + m2u2 = m1v1 + m2v2
CHAPTER 1 MOTION
MOTION ALONG A STRAIGHT LINE
When a body moves in a straight line, it is said to exhibit motion along a straight line.
Distance: The total path length covered by an object is the distance travelled by it.
Displacement: The shortest distance measured from the starting point to the final point is called the displacement of the object. If the final position of the body is the same as the initial position, displacement is said to be zero.
If an object travels equal distances in equal intervals of time, it is said to exhibit uniform motion.
If an object travels unequal distances in equal intervals of time, it is said to be in non-uniform motion.
Speed is the rate at which the body moves i.e. how fast or slow it moves. The speed of the body is the distance travelled by it divided by the time taken to cover that distance. The SI unit of speed is metre per second.
Speed= (Distance travelled)/(Time taken)
The quantity that specifies both the speed and direction of the motion is called velocity.
Average velocity= (Initial velocity+final velocity)/2
The rate of change of velocity is called acceleration.
Acceleration (a) =(Change in velocity)/(Time taken)
The SI unit of acceleration is ms-2.
EQUATIONS OF MOTION
There are three equations of motion:
UNIFORM CIRCULAR MOTION
If an object moves in a circular path with uniform speed, its motion is called uniform circular motion. If the radius of the circle is r,
v=(2 π r)/t
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