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When you try to get down from a moving train why do you fall in the forward direction?

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Why need to try to get down from a moving train we get the phone in the forward direction because of the inertia of motion. The full body of us remains in dynamic condition inside the moving train. But when we try to get down from the moving train, below the parts of our body become static. Fore inertia of moving parts of the upper body is dynamic. That's why when we try to get down from a moving train, we fall in the forward direction.

State the relation between the impulse of Force and the change of momentum.

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The relation between the impulse of Force and change of momentum: Change of momentum = force x time. The product of force and time is defined as the impulse of force. Therefore, the impulse of force = the change of momentum.

Explain how the concept of inertia is obtained from Newton's first law of motion.

From Newton's first law of motion, we observe that body cannot change its state by itself. If the body is at rest, it tends to remain at rest forever, and if it is in motion it tends to remain in motion with uniform speed forever. This property of a body is called inertia. Thus, from Newton's first law of motion, we get the concept of inertia.

Explain the impulse of Force.

The impulse of Force is the multiplication of applied force to a body and the application time. If a force F on a body is applied taking a time t then the impulse of Force is F x t. It is generally the change in momentum minus the initial momentum.

How the skydivers descend safely to the ground with the help of a parachute?

A parachute works by harnessing the air resistance. Air resistance is a type of frictional force that works against the force of gravity on Earth. As an open parachute has a large surface area, it helps provide enough air resistance. As a result, the skydivers falling speed is decreased mostly. So, the skydiver will then be able to descend slowly and safely.

If a stationary bus suddenly starts moving, the passengers lean backward - why?

If a stationary bus starts moving, the passengers inside the bus lean backward because the passengers wish to remain in their initial state of rest. This is known as inertia. As the bus starts to move, the passengers who are initially at rest will continue to remain at rest and So, they lean backward for an instance of time.

Explain how we walk.

In our daily life, you walk or run on the ground. When we walk on the ground, we accept a backward force on the ground by the leg behind obliquely. This is the action force. According to the third law, a reaction force is produced opposite to this. We are able to walk on the road due to this reaction force.

When a shot is fired from a gun, the gun pushes backward why?

When a shot is fired from a gun the gun is pushed backward at the time. In this case, the action and reaction force off the bullet and the gun exist at the same time.  According to Newton's second law of motion, the bullet and the gun equal and opposite momentum. As a result, the bullet moves forward with a particular momentum and the gun moves backward with a momentum of the same magnitude but opposite in direction. Due to this, the person will feel a backward thrust. The backward velocity of the gun will be smaller in compression to that of the bullet is the mass of the gun is large.

Write down the advantages of friction.

Though fiction has many advantages it is considered a necessary evil. We cannot do anything without the force of friction. If there was no friction, the motion of a body would not cases at all and continue perpetually. Due to friction, a nail is fixed in a wall. It became possible to construct buildings and houses because of friction. We can work as there is friction between our shoes and the ground. We can change the direction of motion of a car owing to fiction. Using a parachute it is possible to descend safely to the ground by Honey Singh the resistance. So, we can say that friction has so many advantages in our daily life.

Why does deceleration occur when a moving car is suddenly braked?

Velocity of a car decreases when it is suddenly braked, as a result deceleration occurs. In this case, the velocity is decreased by applying force opposite to the motion of the car. Deceleration is the decreasing rate of velocity with time. This is why deceleration occurs when a moving car is suddenly braked . 

What is inertia of motion?

When a body tends to remain in motion because of velocity then it is called inertia of motion. So, the characteristic of a body in motion wanting to keep its motion is called the inertia of motion . The inertia of the motion of a body depends on its momentum. When a moving bus is suddenly stopped, people bend forwards due to the inertia of motion . 

How to get the concept of inertia from Newton's first law?

 According to Newton's law, a stationary object will remain stationary and an object in uniform motion will continue its uniform motion. From Newton's first law, a force should be applied to change the stationary and motion state of a body. The characteristics of a body to keep its safe is called inertia.

Explain Pascal's law.

Pascal's law is a principle in fluid mechanics given by Balise Pascal that states that a pressure change at any point in a confined incompressible fluid is transmitted throughout the fluid such that the same change occurs everywhere. 

What is called pressre?

 Pressure is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. 

Friction is a necessary evil - give an argument in favor of it.

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Friction is a necessary evil - give an argument in favor of it. Friction is considered a necessary evil. We cannot do anything without the force of friction. If there was no friction, the motion of a body would not cease at all and continue perpetually. Friction has made it possible to write on paper with a pencil or a pen. We can walk as there is friction between our shoes and the ground. To make life and works easier we need friction.  When an object moves or tends to move over another object, this resistance is known as friction. Friction is called a necessary evil on the ground that it is necessary in spite of having certain disadvantages. To speak about the necessity of friction, what comes first is that the motion of a body would never cease but would continue perpetually if there were nothing to be friction. It plays a vital role in our practical life. It makes contracting buildings, houses, and bridges possible. We could not even fix a nail if there were no friction. Friction h

Why cooking at the top of hill is difficult?

At higher altitudes, like hills, cooking food is difficult. Higher altitudes mean lower atmospheric pressure. The boiling point decreases if the pressure is low. So, at the top of the hill cooking takes a long time because due to lower pressure water starts to boil at comparatively lower temperatures. As the temperature cannot be increased, so it takes a longer time to cook. 

The velocity of a body moving with uniform speed may not be uniform.

 We know, velocity is a vector. It has both value and direction. So, change in direction or value will result in change of vector. So, if direction of an object going at uniform velocity changes, velocity will also change. Meaning, uniform speed does not always mean uniform velocity.

Applications of UV and IR Light

Ultraviolet light produces reactions in the skin then visible light. Some of these reactions are beneficial and some are harmful. One of the major beneficial effects of UV light from the sun is the conversion of molecular products in the skin into vitamin D. Ultraviolet light from the sun affects the melanin in the skin to cause tanning. However, UV light can produce sunburn as well as tan skin. Solar UV light is also the major cause of skin cancer in humans. The eye cannot see ultraviolet light because it is absorbed before it reaches the retina. About half of the energy from the sun is in the IR region. The warmth we fell from the sun is mainly due to the IR component. The IR rays are not usually hazardous-even though the cornea and lens of the eye onto the retina focus them. Our eyes also cannot see IR light.

Walls of the Heart

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The walls of the heart consist of layers of muscle, wound several times around the atria and the ventricles in a complicated arrangement. The layers of muscle around the ventricles are thicker than those around the atria. The heart muscle pumps blood by its cyclic contractions and relaxation. The contracted phase of the heart is called systole, and the relaxed phase is called diastole. Each contraction begins in the walls of the atria, and this squeezes the blood from the atria into the ventricles; a moment later, the walls of the ventricle contract. Squeezing the blood out of the heart into the ventricles; a moment later, the walls of the ventricle contract, squeezing the blood out of the heart into the arteries. Since the walls of both atria contract jointly, and the walls of both ventricles also contract jointly, the right and the left pumps in the heart always operate in unison. The layers of muscle around the left ventricle are much thicker than those around the right ventricle. T

The Chambers and Valves of the Heart

Each of the pumps in the heart has two chambers. The upper chamber is called the atrium, and the lower chambers the ventricle (“belly”). The atria accumulate the blood arriving at the heart and then inject it into the ventricles. The ventricles eject the blood from the heart into the arteries; they perform most of the work required for the pumping. Each pump has two flap valves. The right pump has the tricuspid valve (between the atrium and the ventricle) and the pulmonary valve (at the beginning of the pulmonary artery). The left pump has the mistral valve (between the atrium and the ventricle) and the aortic valve (at the beginning of the aorta). These flap valves operate passively; their leaflets bend open to permit the flow of blood in the forward direction; but they flip shut when there is an incipient flow in the backward direction. We can best understand the operation of the chambers and the valves of the heart by tracing the flow of a parcel of blood through the heart and aroun

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Md. Saifur Rahman


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

Former Principal of South Point School and College, Dinajpur.

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