Category: Science

Force

A body needs a ‘push’ or ‘pull’ to move or to bring a moving body to rest or change its velocity. Hence this push or pull is called force. Force has both magnitude and direction. Therefore force is a vector quantity.

Definition of force in physics

Types of Forces

Force is classified into types as:

• Like parallel force – Two or more forces of equal or unequal magnitude acting along the same direction, parallel to each other.
• Unlike parallel force – Two or more forces either equal or unequal forces act in opposite directions parallel to each other.

Unit of Force: SI unit of force is newton(N) and in the C.G.S system its unit is dyne.

Definition of 1 newton (N) – The amount of force required for a body of mass 1 kg to produce an acceleration of 1 kg⋅m/s².

1 N = 1 kg m/s²

Dyne

One dyne is the amount of force required for a body of mass 1 gram produces an acceleration of 1 cm/s^-2.

1 dyne = 1 g cm/s^-2 ; also 1 N = 10⁵ dyne.

Unit Force

The amount of force required to produce an acceleration of 1 ms^-2
in a body of mass 1 kg is called ‘unit force’.

Gravitational unit of force

The gravitational unit of force is kilogram-force, represented by kg f in SI units. In the C.G.S system, its unit is gram force, represented by gf.

1 kg f = 1 kg × 9.8 ms^-2 = 9.8 N;
1 g f = 1 g × 980 ms^-2 = 980 dyne

Issac Newton formulated three laws of motion.

• Newtons 1st Law
• Newtons 2nd Law
• Newtons 3nd Law

These three are discussed later in the notes.

Mechanics

Mechanics is a branch of physics that studies the effect of force on bodies. It is divided into Statics and dynamics.

• Static – Static deals with the bodies that deal with the bodies that are at rest under the action of force.
• Dynamics – Dynamics deals with moving bodies under the action of forces. Dynamics is further divided into Kinematics and Kinetics
  • Kinematics – Kinematics studies the motion of bodies without considering the cause of movement.
  • Kinetics – Kinetics studies the motion of bodies considering the cause of movement.

Inertia

When a force is applied to bodies, they resist change in their state. This property is called Inertia.

Example: We tend to move forward when the bus suddenly stops. Or We move backwards when the bike starts suddenly.

Inertia is defined as the interesting property of a body to resist the state of rest state of uniform motion unless it is influenced by an external unbalanced force.

Types of Inertia

• Inertia of rest – The resistance of a body to change its state of rest is known as Inertia of rest.
• Inertia of motion – The resistance of a body to change its state of motion is called Inertia of motion.
• Inertia of direction – It is the resistance of a body to change its direction of motion is called Inertia of direction.

Linear Momentum

Linear momentum measures the impact of force on a body. The impact of a force is more when the velocity and the mass of the body are more.

The product of mass and velocity of a moving body provides the magnitude of linear momentum. It acts in the direction of the velocity of the object.

Linear Momentum = Mass x Velocity

That is: p = mv. It helps to measure the magnitude of a force.

The unit of momentum in the SI system is kg ms^-1and in the C.G.S system, its unit is g cms^-1.

Newton’s Laws of Motion

Newton’s First Law of Motion

This law states that “a body continues to be in its state of rest or state of motion along a straight line unless an external force at act on it”.

This gives the definition of force as well as inertia.

Newton’s Second Law of Motion

According to this law,” The force acting on a body is directly proportional to the rate of change of linear momentum of the body. And the change in momentum takes place in the direction of the force.”

This law is used to measure the amount of force. So this is also called as ‘law of force‘.

F = m x a

Force = mass x acceleration

Newton’s Third Law of Motion

This law states that ‘for every action, there is an equal and opposite reaction ‘.

Example: Recoil of Gun, Swiming, Birds flying etc.

Principal of Conservation of Linear Momentum

As per this principle, there is no change in the linear momentum of a system of bodies as long as no net external force acts on it.

Moment of Force

The rotating effect of a force about a fixed point or fixed axis is called the moment of the force about that point or torque (τ). Torque is a vector quantity and its SI unit is N m.

The torque is measured by-product of the force (F) and the perpendicular distance (d) between the fixed point or axis and the line of action of the force.

τ = F × d

Couple

When two equal and unlike parallel forces are applied simultaneously at two distinct points, is a couple.

The line of action of the two forces does not coincide and does not produce translator motion. This is because the resultant is zero. But a couple causes the rotation of the body.

This rotating effect of a couple is called the moment of a couple. The unit of the moment of the couple is Newton metre (N m) in the SI system and dyne cm in the C.G.S system.

Example: Turning of Tap, winding a Screw, Spinning of top

Moment of a couple = Force × perpendicular distance between the
line of action of forces

M = F x S

Conclusion

This article is for Tnpsc, for the topic ‘Force‘. This article provides a brief description of basic concepts of force in Physics. For detailed notes please refer to the Samacheer Kalvi book, Science 10th Std, Unit-1, Laws of Motion.

Bones and Joints

The adult human skeleton consists of 206 bones. The bones along with approximately 700 skeletal muscles account for 50% of our body weight.

Bones provide protection and support. When two or more bones join together, a joint or articulation is formed. Several types of joints help in movements.

Muscles

Muscles are elastic in nature. They are capable of contraction in response to stimuli from the central nervous system. The muscle cells function like biological machines that convert chemical energy into mechanical work.

The mechanical work involves various movements including vital processes like contraction of the heart and blood vessels. Approximately 40% of the body is skeletal muscle and almost 10% is smooth and cardiac muscles.

Structure of a Skeletal Muscle

A striated muscle is composed of many fibers arranged in bundles. The diameter of each fiber varies from 10 to 100 microns. The length of fibers ranges from 1 to 20mm.

Each fiber is surrounded by a membrane called the Sarcolemma. Each muscle fiber is made up of 4 to 20 thread-like structures called myofibrils.

They are parallel to each other. The myofibrils are 1 to 3 microns in diameter. In between the myofibrils, the sarcoplasm is present. A small segment of the myofibril is called the sarcomere.

Structure of Sarcomere

When a sarcomere is observed under a microscope we could see alternative dense (A band) and light bands (I band). The central region of the A band is often less dense and is known as the “H Zone“.

The ‘I band’ is bisected by a dense narrow line, the Z line. Thus each sarcomere includes repeating units between two Z lines in linear order as Z line, I band, A band, I band, and next Z line. There is the regular arrangement of 2 types of protein filaments.

A band contains a set of thick filaments formed of the contractile protein myosin. It may range up to 110 A in diameter and 1.5 microns in length. The second set of thin filaments (50 A diameter) overlaps the long filaments in the A band.

The second set of filaments extend partly in ‘I band’ and partly in ‘A band’. These filaments are formed of a substance called Actin.

Classification of Materials

Solids are classified into insulators, metals, and semiconductors.

Insulators

The valence band and the conductor band are separated from each other by an enormous energy gap. The energy gap between the valence band and the conductor is approximately 6eV.

The energy gap is enormous, and even high voltage or electric field or change in temperature, does make conduction. The electrical conduction is not possible as there are no free electrons. These materials are called insulators and their range of resistivity is 10¹¹ – 10¹⁹ Ωm.

Metals

In valence band and conduction band overlaps in metals. The electrons can flow freely into the conduction band which results in a large number of free electrons in the conduction band.

Thereby, even at low-temperature conduction is possible. The resistivity range between 10^-12 to 10^-8 Ωm.

Semiconductors

Semiconductors, a thing is forbidden energy gap (E_g < 3eV) endures among the valence band and the conductor band. At a limited temperature, thermal disturbance in the solid can destroy the convent bond between the atoms.

That covalent bond is developed due to the distribution of electrons to attain a steady electronic configuration. This loosens some electrons from the valence band to the conduction band.

Since free electrons are little in quantity, the conductivity of the semiconductors is not as big as the conductors. The resistivity ranges of the semiconductor 10^-5 to 10⁶ Ωm. In semiconductors, electrons in the valence band are bound electrons that cannot move and contribute to conduction.

When the temperature is raised more, a larger number of electrons is forwarded to the conduction band and the conduction is increased. Thus, the electrical conduction increases with the increase in temperature in the semiconductors.

Hence, “semiconductors have a negative temperature coefficient of resistance”. Examples of semiconductors are Silicon (Si) and Germanium (Ge). The energy gap for Silicon and Germanium at room temperature are 1.1 eV and 0.7 eV.

What is an oscillator?

The oscillator is a mechanical or electrical apparatus that produces periodic fluctuation. Or it is a device that produces a repeated waveform.

This signal can be a sine wave, a square wave, or a triangle wave. Oscillators are used in a wide variety of electronic devices, including clocks, radios, computers, and synthesizers.

The basic principle of an oscillator is to use positive feedback to amplify a signal and then feed it back into the input of the amplifier. This creates a loop that sustains the oscillation. The frequency of the oscillation is determined by the components in the feedback loop.

There are two main types of oscillators: linear and nonlinear. Linear oscillators produce a sinusoidal signal, while nonlinear oscillators produce a square wave or triangle wave.

Some common examples of oscillators include:

• RC oscillator: This type of oscillator uses a resistor and a capacitor to create the feedback loop.
• LC oscillator: This type of oscillator uses an inductor and a capacitor to create the feedback loop.
• Crystal oscillator: This type of oscillator uses a crystal to create a very precise frequency.
• Piezoelectric oscillator: This type of oscillator uses a piezoelectric crystal to create an oscillating signal.

Oscillators are essential components in many electronic devices. They are used to generate clock signals, control the frequency of radio waves, and produce audio signals. Oscillators are also used in a variety of other applications, such as medical imaging and telecommunications.

Here are some of the applications of oscillators:

• Clock signals: Oscillators are used to generate clock signals in computers, digital watches, and other electronic devices. The clock signal is used to synchronize the operation of the device.
• Radio waves: Oscillators are used to generate radio waves in radios, televisions, and other wireless devices. The frequency of the radio wave determines the channel that the device is tuned to.
• Audio signals: Oscillators are used to generate audio signals in speakers, headphones, and other audio devices. The frequency of the audio signal determines the pitch of the sound.
• Medical imaging: Oscillators are used in medical imaging devices, such as ultrasound machines and MRI scanners. The oscillators are used to generate the high-frequency waves that are used to create the images.
• Telecommunications: Oscillators are used in telecommunications devices, such as cell phones and satellite receivers. The oscillators are used to generate the signals that are used to transmit and receive data.

An oscillator converts

What is oscillation?

It’s a movement back and forth. Example: Pendulum of a clock. hands of the clock.

Transistor as Oscillator

An electronic oscillator basically converts dc energy into ac energy of high frequency ranging from a few Hz to several MHz. There are two types of oscillators: one is Sinusoidal and Non-Sinusoidal.

Sinusoidal oscillators generate oscillations in the form of sine waves at constant amplitude and frequency. Whereas non-sinusoidal oscillators generate complex non-sinusoidal waveforms like a square wave, triangular wave, or Sawtooth wave.

Sinusoidal oscillation can be of two types: Damped and Undamped. If the amplitude of the electrical oscillation decreases with time due to energy loss is called Damped oscillation.

On the other hand, the amplitude of the electrical oscillation remains constant with time in undamped oscillation.

Application of Oscillator

• To generate periodic sinusoidal or non-sinusoidal waveforms.
• To generate RF carriers
• To generate audio tones
• To generate a clock signal in digital circuits
• Sweep circuits in TV sets and CRO.

Optoelectric devices

The devices that convert electrical energy into light and light into electrical energy through semiconductors.

Example of Optoelectric devices is Light-emitting diodes, photodiodes, and solar cells.

Light Emitting Diode (LED)

LED is a p-n junction diode that emits visible or invisible light when forward biased. The electrical energy is converted into light energy and this process is called electroluminescence.

The color of the light is determined by the energy bandgap of the material.LEDs are available in a wide range of colors such as blue (SiC), green (AlGaP) and red (GaAsP), white (GaAsP).

Application of LED

• Indicator lamps
• Seven segment display
• Traffic signal

Photodiodes

A p-n junction diode that converts the optical signal into an electric current is called a photodiode. The operation of the photodiode is exactly the opposite of LED.

Photodiode works in reverse bias. Photodiodes can generate current when the p-n junction is exposed to light and are called light sensors.

Applications of Photodiodes

• Alarm
• Count items in conveyor belts in industries
• Photoconductors
• Compact disk players
• Smoke detectors
• A medical application such as detector for computer tomography etc

Solar Cell

A solar cell is also called a photovoltaic cell that converts light energy into electricity or electric potential difference by the photovoltaic effect.

A solar cell is of two types- p-type and n-type. Many solar panels are connected with each other to solar arrays.

For high power applications, solar panels and solar arrays are used.

Application of Solar Cell

• Used in calculators, watches, portable power suppliers.
• Power supply for satellites and space modules.
• Solar panel used to generate electricity