Grade 9 AY Physics

Physics NCERT

(SA) State the Universal Law of Gravitation

The force of attraction between any two bodies in the universe is directly proportional to the product of the masses and inversely proportional to the square of the distances between them.

(F) Gravitational Force

F = Gm₁m₂/r²

(V) Universal Gravitation Constant

6.67 × 10⁻¹¹ Nm²/kg²

(LA) Applications of Universal Law of Gravitation

1. Force that binds us to the earth

2. Motion of moon around the earth

3. Motion of planets around the sun

4. Waves are caused by the gravitational attraction by the moon

5. Rivers flow on earth due to the gravitational pull on the river by the water.

(D) Centripetal Force

The force that keeps a body in circular motion and acts towards the centre

(V) Mass of the Earth

6 × 10²⁴ kg

(V) Radius of the Earth

6.4 × 10⁶ m

(D) Free Fall

The motion in which a body falls towards the earth only infludenced by the earth’s gravitational force.

(F) Value of g

g = GM/R²

(SA) Differentiate between mass and weight

Weight

1. The force with which the object is attracted towards the earth

2. It is a vector quantity

3. It changes from place to place

4. It is zero at the centre of the earth

5. SI Unit is Newton

Mass

1. The quantity of matter contained in a body

2. It is a scalar quantity

3. It does not change from place to place

4. It can never be zero

5. SI Unit is Kilogram

(SA) How does the value of g change.

The value of g decreases as we go further down under the arth and it becomes zero at the centre.

(F) What is used to measure weight of the body

Spring Balance

(F) What is used to measure mass

Physical Balance / Pan Balance / Beam Balance

(F) Pressure

Pressure (P) = Thrust (T) / Area (A) N/m²

(D) Thrust

The force acting on an object perpendicular to the surface

(D) Pressure

Pressure is the force acting perpendicularly on a unit area of an object.

(LA) Applications of Pressure

1. Handles and straps of bags are made broad to reduce load

2. Base of buildings are made broad to reduce force on the ground.

3. Wheels of tractors are made broad to avoid is damaging the field and sinking into the ground.

4. Nails , Screws and knives are made pointy at the end to make it easier to penetrate.

(SA) How do fluids exert pressure?

Fluids exert pressure on the walls of the container they are enclosed in , in all directions.

(D) Buoyancy

Tendency of the liquid to exert an upward force on an immersed object.

(D)Buoyant Force

The upward force which a liquid applies on an. object immersed in it.

(SA) Factors Affecting Buoyancy

1. It is directly proportional to the density of the object

2. It is directly proportional to the volume of object immersed in the object.

(D) Density

Denisty is defined as mass per unit volume.

(SA) State the Archemedies Principle

When an object is fully or partially immersed in a liquid it experiences a buoyant force or upthrust which is equal tot he weight of the liquid displaced by the object.

(SA) Applications of Archimedes Principle

1. Designing ships and submarines

2. Lactometer - device used to determine the purity of milk.

3. Hydrometer - device used to determine the density of a liquid.

(F) Buoyant Force

Buoyant Force = Weight of liquid displaced by the object.

(D) Work

Work can be defined as the product of force and displacement

(F) SI unit of Work

Joule

(D) Postive Work

When force and dispalcement are in the same direction psitiive work is done

(D) Negative Work

When force and displacement are in opposite directions negative work is said eto be done.

(D) Zero Work

When the force applied is perpendicular to the direction of force applied the work doen is said to be negative.

(D) Energy

Energy can be defined as the capacity to do work

(F) 1kJ = x J

10³ J

(SA) State the work energy theorem

Whenever a force is applied on the body and i gets displaced , work done is equal to the change in kinetic energy of the body.

(D) Kinetic Energy

The energy which is possessed by an object by virtue of its motion is called kinetic energy.

(D) Potential Energy

The energy possessed by the body due to its change in position or shape is called potential energy.

(SA) State the law of conservation of energy.

Energy can neither be created nor destroyed it can be converted from one form to another. The total amount of energy for an isolated system in the universe is always constant.

(D) Power

The rate of doing owrk or the rate at which energy is transferred or used or transformed to other form is called power.

(F) SI Unit of Power

Watt in honour of James Watt

(F) Average Power

Average Power = Total Energy Consumed / Total Time Taken

1 Horse Power = y Watts

746

(D) Sound

Sound is a form of energy which produced a sensation of hearing in our ears.

(D) Mechanical Waves

Waves that require a medium to travel

(SA) Propagation of Sound

1. When an object vibrates it exerts a force on the particle of the medium displacing it from its equilibrium position.

2. The displaced particle displaces it’s adjacent particle and comes back to rest

3. This process continues till the sound reaches our ears

(D) Compressions

Compression is part of the longitudinal wave in which the particles of the medium are closer to one another and it is the region of high compression.

(D) Rarefactions

Rarefaction is the part of a longitudinal wave in which the particles of the medium are farther apart than they normally are and it is the region of low pressure.

(D) Longitudinal Wave

Longitudinal waves have individual particles of the medium move in a direction parallel to the direction of propagation of the disturbance.

(D) Transverse Wave

The individual particles move about its mean position in a direction perpendicular to the direction of wave propagation is called a transverse wave.

(D) Wavelength

The distance between two consecutive rarefactions or two consecutive compressions.

(D) Frequency

The number of oscillations of the wave in one second.

(F) SI unit of Frequency

Hertz ( Heinrich Rudolf Hertz)

(D) Time Period

Time taken by two consecutive rarefactions or compressions to cross a fixed point is known as time period. or the time required to produce one complete oscilation

(F) Time Period

Time Period = 1/ Frequency

(D) Amplitude

The maximum displacement of a particle of the medium from it’s mean position is known as amplitude.

(D) Speed

Distance travellled by the wave in one second

(F) Speed of Sound

V = µλ

(D) Loudness

MEasure of sound energy reaching the ear per second. The greater the sound energy the louder the sound will appear to be.

(D) Intensity

The amount of sound energy passsing each second through a unit area.

(F) SI unit of inensity

W/m²

(D) Pitch of Sound

Pitch of the sound is directly realted to the frequency of the sound.

Speed of sound in air

340 m/s

(D) Reflection of Sound Wave

The bouncing back of sound when it strikes a hard surface

(D) Echo

The repetition of sound caused by multiple soudn waves is called echo.

(D) Reverberation

The persistance of sound due to multiple repeated reflections is known as reverberation.

(LA) Applications of multiple reflections of sound

1. Megaphone - large cone shaped device used to amplify the voice of a person. The cone shaped walls cause successive reflections and prevent the sound from spreading making it heard over long distances

2. Stethoscope - multiple reflections occur in the stethoscope tube causing the sound to reach the doctors ears.

3. Sound board - curved or concave boards are placed in big halls to spread the sound evenly across the hall.

(D) Infrasonic Sound

Sound waves with frequency less than 20 Hz

(F) Hearing range of elephants and rhino

5 Hz

(F) Ultrasonic hearing range of dogs

5000 Hz

(F) Which animals can produce utrasonic sound

Dolphins , bats , porpoises

Applications of Ultrasound

1. Echocardiography

2. Ultrasonography

3. Break down kidney stones

4. Clean parts. by putting in liquid

5. Detect cracks and flaws in metals

(LA) Differentiate between Distance and Displacement

Distance

1. The length of the actual path travelled by the object n given interval of time

2. It is a scalar quantity

3. It is always positive

4. It depends on the path travelled by the object

5. It is always equal or greater than displacement

Displacement

1. The shortest distance between initial and final position of an object moving in a particular direction

2. It is always negative.

3. It can be positive , negative or zero

4. It only depends on the initial and final position

5. It is always equal or less than the distance

(D) Uniform Motion

The motion of an object is considered to be uniform if it covers equal disrtances in equal intervals of time

(D) Non Uniform Motion

The motion of an object is considered to be mom uniform if it does not cover equal distances in equal intervals of time

(D) Uniform Speed

If the object is said to have uniform speed if it cover equal distance in equal intervals of time

(D) Non Uniform Speed

An object is said to be in non uniform speed if it covers unequal distance in equal intervals of time.

(D) Average Velocity`

It is defined as the ratio of total displacement covered by a body to the total time taken by it.

(D) Resultant Force

The resultant force is when a force acting on a body produces the same effect as that produced by a number of forces.

(D) Inertia

The property of the body by virtue of which it opposes any sort of change in it’s state of motion.

(D) Momentum

The product of mass and velocity of the object of a body. It is a vector quantity

(D) First Law of Motion

A body continues to be either in state of rest or uniform motion along a straight line unless an external force is applied on it.

(D) Second Law of Motion

The rate of change of momentum is directly proportional to the applied force and take place in the same direction as the applied force.

(D) Third Law of Motion

It state that to evry action there is an equal and opposite reaction. Action and reaction forces are equal but act in the opposite direction.

(D) Impulse

it is the change in momentum of the body.

(F) Impulse

Ft = mv - mu