HEAT AND TEMPERATURE

PERIODIC AND OSCILLATORY MOTION

Any motion which repeats itself in equal interval of time is called a periodic or harmonic motion. For-example, the motion of the planets around the sun, the motion of the satellites around their corresponding planets, the motion of flywheel in a machine etc are some examples of periodic or harmonic motion. If the particles in the periodic motion move back and forth, the motion is called oscillatory or vibratory motion. We have a lot of examples of oscillatory or vibratory motion. For example, the motion of pendulum of a pendulum clock, the motion of balance wheel of a watch, the motion of air molecules when sound travel through air, the motion of the atom in molecules, the motion of the strings of a guitar or violent etc are examples of vibratory motion. Similarly the variation of electric and magnetic fields vectors in electromagnetic waves such as light waves, microwaves, radio waves etc are also vibratory motions.
One of the common properties of all the vibratory motion is that they can be expressed as a sine or cosine function of time.

CENTRIPETAL FORCE

If a body moves in a circular path with a constant angular velocity, it has a constant linear velocity along the circumference of the circular path. When the body moves along the circle, the direction of velocity changes at every point on the circle. However, the magnitude of the velocity remains the same. The change in direction of the velocity of the particle moving in the circle implies that the particle has acceleration. If a particle has acceleration, a force must have acted upon it to cause the acceleration. This implies that if a body is moving uniformly in a circle, a force is acting on the body at every point; the force changes the direction of the velocity keeping the magnitude constant. The direction of velocity of the body at any point on the circle is tangent to the circle at the point. The force that acts on body moving in a circle towards the center of the circle is called centripetal force. The acceleration thus produced on the body due to the centripetal force is called centripetal acceleration.

PRINCIPLE OF CONSERVATION OF ENERGY

The energy is a conserved quantity. The energy of an isolated system remains the same. The energy can neither be created not can be destroyed. It can be changed from one form to another form. For example, if a stone is thrown up with a velocity, initially, it has maximum velocity and hence maximum kinetic energy. When it moves up, its velocity goes on decreasing. At a certain height, its velocity becomes zero, and hence its kinetic energy becomes zero. At the same time, when the stone moves up, it gains height. As it gains height, its potential energy increases. Hence, it is clear that when a stone is thrown up, its kinetic energy goes on decreasing while its potential energy goes on increasing. However, the total energy of the stone remains the same. This is the principle of conservation of energy.




According to the principle of conservation of energy, the energy can neither be created nor be destroyed but can be changed from one form to another form.

FRICTION

Modern theory: It has been found that if two surfaces in contact are highly polished, the force of friction increases. This implies that when the two surfaces in contact are highly polished, their molecules come in contact in the range of intermolecular distance. When the molecules are at distances of intermolecular range, the intermolecular forces of attraction between them become significant. When the intermolecular force of attraction between the molecules of the two surfaces in contact is significant, the sliding body has to overcome the intermolecular force of attraction. And, hence, the force of friction between the surfaces increases. When the smoothness of the surfaces is increased, more number of molecules come into the intermolecular range. As a result, the intermolecular force increases and the friction increases.

EQUILIBRIUM OF FORCES

If a number of forces are acting on a body and the net force on the body is zero, the body is said to be in linear equilibrium. Hence, for a body in linear equilibrium, the net force is zero. The zero net force implies that the acceleration of the body is zero. If a body has zero acceleration, there are two possibilities: one is that the body is at rest under the action of a large number of forces, the body is said to be in static equilibrium. Similarly, if the body is moving with uniform velocity under the action of a large number of forces, the body is said to be in dynamic equilibrium.

Newton’s III Law of Motion

Newton’s third law of motion states that to every action, there is an equal and opposite reaction. That is, in any pair of bodies acting forces on each other, force exerted by one on the other is equal in magnitude and opposite in direction to the force exerted by the second body on the first body. That is
If you give a slap to a child, the child cries due to pain. The pain is caused due to the force exerted on him. At the time the child feels pain; you also feel pain on your hand. The pain on your hand must be due to some force acting on your hand. What is that force? In fact, when you give a slap to the child, you apply force on the child’s face. At the same time, the child’s face also exerts force on your hand. The pain on your hand is due to the force exerted by the child’s face on your hand. The force exerted by your hand on the child’s face is called action. The force exerted by child’s face on your hand is called reaction. Hence, the action and reaction are forces which act on different bodies. The action is the causes and the reaction is the effect.

Newton’s II Law of Motion

Newton’s second law of motion gives a relationship between force and acceleration. In fact, it gives a measurement of force on a body.







When a car starts from rest, its velocity goes on increasing. The engine of the car applies force on it to change the velocity. Similarly, if brakes are applied on the moving car, the velocity of the car goes on decreasing. In this case, the brakes of the car apply force to decrease the velocity. In both cases, there is a change in velocity. The change in velocity is a measure of acceleration. Hence, if a force is applied, there is a change in velocity and hence there is acceleration. Conversely, if there is a change in velocity, there must be force acting on the body. This implies that there exists a relationship between the force applied and the acceleration produced on a body. Newton established the relationship between the force acting on a body and the acceleration produced on it. The relation is known as Newton’s II law of motion.

Newton’s I Law of Motion

Statement: Newton’s First law of motion states that every body in this universe continues in its state of rest or uniform motion in a straight line unless it is acted upon by an external force.



a. This means that if a body is at rest, it remains at rest until an external force compels it to change the rest state. Similarly, if a body is in motion, it continues to be in motion unless an external force compels it to change its motion state. This in facts is called law of inertia. Hence, Newton’s first law of motion is also known as law of inertia.
Examples: In our daily life, there are a large number of examples where Newton’s first law of motion can be applied. Out of these, the following are some of the most common examples:


When a papaya tree is shaken, the papaya falls

When a moving bus suddenly stops, the passengers sitting in it fall forward.


 When a horse at rest suddenly starts moving, the horse rider falls backward.

SI system

The CGS, MKS and FPS systems used only three fundamental quantities (mass, length and time) for the measurement of a physical quantity. However, these three fundamental quantities were found insufficient to measure some physical quantities in thermodynamics, optics and current electricity. For example, the amount of current in a circuit could not be expressed in terms of mass, length and time. To solve the problem, another system of unit called SI(System International de Units) units came into existence. In fact, the international convention of scientists held in France in 1968 decided to use the SI units. In addition to mass, length and time as the fundamental quantities, the SI units added a few more quantities as the fundamental quantities. They are temperature, electric current, luminous intensity and amount of substances.