ICSE Class 9 Physics Syllabus

Define one newton of force.

One newton is the force that produces an acceleration of 1 m/s² in a body of mass 1 kg (1 N = 1 kg·m/s²).

State Newton's Third Law of Motion.

To every action there is an equal and opposite reaction; the forces act on two different bodies.

State the law of conservation of momentum.

In the absence of an external force, the total momentum of a system of bodies remains constant before and after their interaction (e.g., collision).

Why are action and reaction forces, though equal and opposite, unable to cancel each other?

Because they act on two different bodies, not on the same body, so they cannot cancel out.

Explain the recoil of a gun using conservation of momentum.

Before firing total momentum is zero. When the bullet moves forward with momentum, the gun moves backward (recoils) with equal and opposite momentum to keep the total zero.

What is the difference between balanced and unbalanced forces?

Balanced forces have zero net effect and do not change a body's state of motion. Unbalanced forces produce a net force that causes acceleration or change in motion.

State Newton's Universal Law of Gravitation.

Every body attracts every other body with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

Write the formula for gravitational force between two masses.

F = G·(m₁m₂)/r², where G is the universal gravitational constant, m₁ and m₂ are the masses, and r is the distance between their centres.

State the value and SI unit of the universal gravitational constant G.

G = 6.67 × 10⁻¹¹ N·m²/kg².

Define acceleration due to gravity (g) and give its average value on Earth.

g is the acceleration produced in a freely falling body due to Earth's gravity. Its average value is 9.8 m/s² (about 9.81 m/s²).

What is the difference between mass and weight?

Mass is the quantity of matter in a body (scalar, constant, in kg). Weight is the gravitational force on the body, W = mg (vector, varies with g, measured in newtons).

How is g related to G, the mass of Earth, and its radius?

g = G·M/R², where M is the mass of the Earth and R is its radius.

Why does the value of g decrease as we go above the Earth's surface?

Because g is inversely proportional to the square of the distance from Earth's centre; as height increases, the distance increases, so g decreases.

What is the weight of a body at the centre of the Earth, and why?

Zero, because at the centre the body is pulled equally in all directions, making the value of g (and hence weight) zero.

State Galileo's law of falling bodies (free fall).

In the absence of air resistance, all bodies fall freely with the same acceleration g, regardless of their mass.

How does the weight of an object differ at the poles versus the equator?

Weight is slightly greater at the poles than at the equator because the Earth's radius is smaller at the poles, giving a larger value of g.

Define work in physics and state its SI unit.

Work is done when a force produces displacement in its own direction; W = F × s × cosθ. SI unit: joule (J).

Define one joule of work.

One joule is the work done when a force of 1 newton displaces a body by 1 metre in the direction of the force (1 J = 1 N·m).

When is the work done by a force zero?

Work is zero when there is no displacement, when the force is zero, or when force is perpendicular to displacement (θ = 90°, cosθ = 0).

Define power and state its SI unit.

Power is the rate of doing work; P = work/time. SI unit: watt (W), where 1 W = 1 J/s.

How many watts are there in 1 horsepower (hp)?

1 horsepower = 746 watts.

Define energy and name its two main mechanical forms.

Energy is the capacity to do work (SI unit: joule). Its two main mechanical forms are kinetic energy and potential energy.

Write the formula for kinetic energy.

Kinetic energy K.E. = ½mv², where m is mass and v is velocity.

Write the formula for gravitational potential energy.

Potential energy P.E. = mgh, where m is mass, g is acceleration due to gravity, and h is the height above the reference level.

State the law of conservation of energy.

Energy can neither be created nor destroyed; it can only be transformed from one form to another, and the total energy of an isolated system remains constant.

For a body falling freely, how do its kinetic and potential energies change while total energy stays constant?

As the body falls, potential energy decreases and kinetic energy increases by an equal amount, so their sum (total mechanical energy) remains constant.

How is sound produced and how does it travel?

Sound is produced by vibrating bodies and travels through a medium (solid, liquid, or gas) as longitudinal waves; it cannot travel through a vacuum.

What are the compressions and rarefactions in a sound wave?

Compressions are regions of high pressure/density where particles are crowded together; rarefactions are regions of low pressure/density where particles are spread apart.

Define frequency, wavelength, and amplitude of a sound wave.

Frequency = number of vibrations per second (Hz); wavelength = distance between two consecutive compressions or rarefactions; amplitude = maximum displacement of particles from their mean position.

State the wave equation relating speed, frequency, and wavelength.

v = f × λ, where v = speed of sound, f = frequency, and λ = wavelength.

In which medium does sound travel fastest—solids, liquids, or gases—and why?

Sound travels fastest in solids because their particles are closely packed and tightly bound, transferring vibrations more quickly (solids > liquids > gases).

What is an echo, and what is the minimum distance needed to hear one?

An echo is the repetition of sound caused by reflection from a surface. To hear a distinct echo the reflecting surface must be at least about 17 m away (so the sound returns after ≥0.1 s).