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What type of quantity weight is - explain.

 Weight is a force that is a vector. So, it has a magnitude and direction. However, mass is a scalar. Weight and mass are related to one another, but they are not the same quantity. Mass is multiplied by the acceleration due to gravity to calculate the weight of an object. Acceleration due to gravity is directed vertically downward.  So, weight is also vertically downward. 

The acceleration of a body is 5 ms-2. What does it mean?

 If the acceleration of a body 5 ms -2  it means that the body is moving with a uniform velocity of 5 ms -1  each second; that is, its velocity is increasing every second at a rate of 5 ms -1 .

A body moving with uniform velocity doesn't have acceleration-explain.

 The rate of change of velocity with the time that is the change of velocity is known as acceleration. It means to be accelerated, the magnitude or direction of the speed of a body must be changed. But if the magnitude of the velocity of a moving body remains unchanged, then the velocity of the body is called uniform or equal velocity.  So, a body moving with uniform velocity doesn't have acceleration.

All rest and motion of this universe is relative. No rest or motion is absolute.

A body is said to be in absolute rest when it is in rest with respect to an absolute rest object. Similarly, absolute motion of a body is its motion with respect to a reference object absolutely at rest. But in this universe, it is not possible to get a reference object which is at absolute rest. Since the earth is continuously moving around the sun, while the sun itself is moving along the galaxy with its planets and satellites. Thus when we say that a body is at rest or in motion, we mean it is to be so with respect to a body apparently at rest. So we can say that in this universe all rest and all motion are relative. No rest or no motion is absolute. 

Ultrasound Images : about various ultrasound images for diagnostics.

Ultrasound Images: about various ultrasound images for diagnostics. X-rays Modern medicine relies heavily on a variety of imaging techniques. They generate pictures of the interior of the human body for diagnostic purposes. The oldest of these imaging techniques is radiography. It generates pictures by irradiating the body with X-rays and recording the shadows of the internal anatomical structures. X-rays give us sharp and clear shadows of the bones, but they are not very well suited for imaging the soft tissues of the body. X-rays cannot discriminate between tissues of approximately equal densities. For instance, when they pass through the heart, X-rays do not discriminate between the heart muscle and the blood filling the heart cavities - an X-ray picture of the heart is merely a blob, which does not reveal the details of the heart’s anatomy. Ultrasound Imaging Several of the newer imaging techniques generate better pictures of soft tissues. Among these newer techniques is ultrasound

Intensity of Sound

A sound wave is intense and loud if it has a large amplitude. However, the amplitude of a sound wave is hard to measure directly, and it is more convenient to reckon the intensity of a sound wave by the energy it carries.  The intensity of a sound wave is defined as the energy per second transported by this wave per square meter of the wavefront, that is, the power transported by this wave per square meter.  Thus, to measure the intensity, we have to erect an area facing the wave, and we have to check how much energy the wave delivers in this area per second. It can be shown that the intensity of a sound wave is proportional to the square of the pressure disturbance it produces in the air; equivalently, the intensity is proportional to the square of the density disturbance. The unit of intensity is the watt per meter squared (W/m 2 ). At a frequency of 1000 Hz, the minimum intensity audible to the human ear is about 2.5 × 10 -12  W/m 2 . This intensity is called the threshold of hearin

Inner Ear

The inner ear is a complex system of fluid-filled cavities in the temporal bone. Among these cavities are the three semicircular canals, whose function is not hearing, but rather the detection of movements of the head. The organ of the inner ear concerned with hearing is the cochlea, a tube of about 3.5 cm coiled in a tight spiral. The tube is divided lengthwise into three adjoining ducts, separated by two membranes, Reissner’s membrane, and the basilar membrane. The sensory receptor of the inner ear is the organ of Corti, consisting of thousands of hair cells, which sit on the basilar membrane. The vibrations of the oval window excite a wave motion in the fluid of the cochlea, which shakes the basilar membrane. The hair cells detect this motion of the basilar membrane and convert the mechanical energy into electric nerve impulses. The basilar membrane is stiff at the end near the oval window, and soft at the distant end. Because of this, the near part of the membrane responds most rea

Middle Ear

The middle ear is an air-filled cavity in the temporal bone of the skull. The cavity is connected to the nasopharynx by the Eustachian tube; this tube permits equalization of the air pressure in the middle ear with the external atmospheric pressure. The middle ear contains three small bones or oscines: the hammer, the anvil, and the stirrup (malleus, incus, and stapes). These ossicles are arranged in a chain from the eardrum to the oval window of the inner ear. The chain of ossicles to the oval window transmits the vibrations generated by a sound wave striking the eardrum. Since the oval window has a much smaller area than the eardrum (about 1/25), the transmission of sound energy from the eardrum to the oval window results in a significant concentration of the energy, with a consequent increase of the amplitude of vibration. Besides transmitting the vibrations from the eardrum to the oval window, the middle ear plays a crucial role in accommodating the ear to very loud sounds. In resp

How Ear Converts Sounds Into Electric Nerve Pulses

The ear performs the task of converting the mechanical oscillations of a sound wave into electric nerve impulses. Thus, it is similar to a microphone, which also converts the mechanical oscillations of sound into electric signals. However, the ear is unmatched in its ability to accommodate a wide range of intensities of sound. The human ear has three main parts: the outer ear, the middle ear, and the inner ear. The outer ear consists of the auricle and the ear canal. The auricle serves to funnel sound waves into the ear, especially waves arriving from the front of the listener. The ear canal is a tube, about 2.7 cm long, closed off at the inner end by the eardrum, or tympanum. The ear canal guides sound waves toward the eardrum, and also enhances sound waves of a frequency of a few thousand hertz, which are in resonance with the standing-wave modes of the air column in the canal.

What is sound wave?

A sound wave in air consists of alternating zones of low and high density. The vibrating diaphragm of a loudspeaker generates such zones of alternating density. The alternating zones of low density and high-density travel to the right away from the source. However, although these density disturbances travel, the air as a whole does not travel, the air molecules merely oscillate back and forth. The pushes of the loudspeaker or of the tuning fork on the air are longitudinal, and the sound wave itself is also longitudinal. The air molecules oscillate back and forth along the direction of propagation of the sound wave. The restoring force that drives these oscillations is the pressure of air. Wherever the density of molecules is higher than normal, the pressure also is higher than normal and pushes the molecules apart; wherever the density of molecules is lower than normal, the pressure also is lower than normal, and therefore the higher pressure of the adjacent regions pushes these molecu

What is Work?

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To introduce the definition of work done by a force, we begin with the simple case of motion along a straight line, with the force along the line of motion, Consider a particle moving along a straight line, say, the x-axis, and suppose that a constant force F, directed along the same straight line, acts on the particle. For example, the particle might be a stalled automobile that you are pushing along a road.  Then the work done by the force F on the particle as it moves some given distance S is defined as the product of the force and the displacement, W = F. S =FSCos α where α is the angle between the force F and the displacement S. Work is a scalar quantity. The unit of work is [W] = [F] [S] In metric system, unit of work is Joule. [W] = 1 Joule = 1 N.m In CGS system, unit of work is erg. Relation between the units of work is 1 Joule = 1 N.m = 10 5 D. 10 2  cm = 10 7  ergs.

Newton’s Laws of Motion

Newton’s Laws of Motion Learning Objectives On completion of this lesson, you will be able to learn- Newton’s first law of motion Newton’s second law of motion Newton’s third law of motion. Newton's three laws of motion give the fundamental properties of force and the relationship between force and acceleration. The first of these laws describe the natural state of motion of a body on which no external forces are acting, whereas the other two laws deal with the behavior of bodies under the influence of external forces. Newton’s First Law Newton’s First Law summarizes experiments and observations on the motion of bodies on which no external forces are acting, thus the first law is - A body at rest remains at rest, and a body in motion continues to move at a constant velocity unless acted upon by an external force.  The tendency of a body to continue in its initial state of motion (a state of rest or a state of uniform velocity) is called its inertia.  Accordingly, the First Law is o

What is mass?

Mass is defined by the quantity of matter of a substance. In general, weight is used to measure an object. It is not correct, weight is the gravitational pull of the earth on the body. The mass of a body remains it everywhere, but the weight may vary. For example, the weights of a body become one-sixth of its value on the moon, since moon’s gravitation is one-sixth of the earth. But mass of the body is same.

What is velocity?

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Velocity is defined as the rate of change of distance moved with time in a particular direction e.g. Velocity is a vector quantity. By vector we mean a quantity, which has both the magnitude and the direction. In metric system, the unit of velocity is same as speed-metre per second (m/s).

What is speed?

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Speed is defined as the rate of change of distance moved with time e.g. Speed is a scalar quantity. By scalar, we mean a quantity, which has only magnitude but no proper direction. For example, movement of the body, movement of substances, movement of medicine, or radioisotopes through a body, all refer to some speed. In the metric system, the unit of speed is meter per second (m/s).

The acceleration of falling body is uniform acceleration.

 Freefall is a special case of motion with constant acceleration because the acceleration due to gravity is always constant and downward. This is true even when an object is thrown upward or has zero velocity. Therefore, the acceleration of a freely falling body is not absolutely uniform, it's rather constant, due to the acceleration due to gravity. 

The position of an object with respect of a point can be changed without changing its distance.

Even if the distance of a body doesn't change with respect to a point but the position of the body might change. For example, the distance with respect to the center from a body revolving in a circular path doesn't change. The value of the position vector of the body changes when the direction of the point changes. So, position changes. 

Differences between Balanced Force and Unbalanced Force

Differences between Balanced Force and Unbalanced Force. No. Balanced Force Unbalanced Force 1 The forces that act on a body and create equilibrium are called balanced force. The forces that act on a body but don't create equilibrium are called unbalanced force.  2 In this case, the resultant of the active forces is zero. In this case, the resultant of the active forces is not zero.

Why is walking hard on a muddy road?

We can easily walk on the road due to the frictional force between the road and the bottom of our feet. But the frictional force between the road and the bottom of our feet decreases in muddy roads. This is why we slip on those roads. So, it is hard to walk on muddy roads. 

Although the speed of the earth around the sun is a periodic motion but not rotational motion

 If the motion of a moving object is such that it passes repeatedly through a definite point in the same direction in the same manner in a definite interval of time, then this motion is called a periodic motion. Earth revolves around the Sun in the same direction in a parabolic path in every 1 year or 365 days, so the motion of Earth is periodic motion. Again, when a body rotates about a particular point or a line, keeping the distance of the particles of the body unchanged, it is called circular motion. Since orbit of Earth is parabolic, so the distance between Earth and Sun isn't always same, this distance is different at different times of the period. So, motion of Earth is not circular motion.

About Me





Md. Saifur Rahman


B.Sc (Honors), M.Sc (Chemistry)

Former Principal of South Point School and College, Dinajpur.

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