CBSE Class 4 Science Physics Worksheet

PHYSICS

Question 1. What do you understand by the term force ?
Answer: A force is a push or pull acting upon an object resulting from the object's interaction with another object. Whenever there is an interaction between two objects, there is a force upon each of the objects. When the interaction ceases, the two objects no longer experience the force. Forces can cause an object to accelerate, decelerate, change direction, or change shape.
In simple words: Force is simply a push or pull applied on an object that can change its motion or shape.

Exam Tip: Remember that force is a vector quantity, meaning it has both magnitude and direction.

Question 2. Explain any two effects of force with examples
Answer: Two main effects of force are:
1. Force can change the state of motion of an object: It can make a stationary object move or stop a moving object. For example, kicking a football from rest makes it move, and catching a moving cricket ball stops it.
2. Force can change the shape of an object: Applying a force on a flexible object can distort its dimensions. For example, pressing a rubber ball or kneading a lump of dough changes its shape.
In simple words: Force can either move/stop things or change how they look by squishing or stretching them.

Exam Tip: Always state the effect clearly and support it with a common daily-life example to score full marks.

Question 3. Identify the two types of forces involved in the following :
Answer: Based on the accompanying picture of a parachute descending, the two primary forces involved are:
1. Gravitational force (Gravity): Pulls the parachute downward towards the Earth.
2. Frictional force / Air resistance (Drag): Pushes the parachute upward against gravity to slow down its descent.
In simple words: The falling parachute experiences a downward pull by gravity and an upward push by air resistance.

Exam Tip: For objects moving through air, always consider gravity and air drag as the core opposing forces.

Question 4. Observe the given picture and identify the effect of force
Answer: Based on the provided picture showing a player hitting a football, the effect of force is that it changes the speed and direction of a moving object (or sets a stationary object into motion). The applied muscular force of the player alters the velocity of the ball.
In simple words: The force applied by the foot changes the position, speed, and direction of the ball.

Question 1. Define the following terms.
a) Filtration
b) Sublimation
c) Sedimentation
d) Distillation
e) Evaporation
Answer:
a) Filtration: A method used to separate insoluble solid particles from a liquid by passing the mixture through a porous material like filter paper.
b) Sublimation: The transition of a substance directly from the solid state to the gas state without passing through the liquid state.
c) Sedimentation: The process in which heavier insoluble suspended particles settle down at the bottom of a liquid over time.
d) Distillation: A process involving the conversion of a liquid into vapor by boiling, followed by the condensation of the vapor back into liquid to purify it.
e) Evaporation: The process by which a liquid turns into a gas or vapor, typically aided by heat, leaving behind dissolved solids.
In simple words: These are various physical methods used to separate different components of mixtures based on their physical properties.

Exam Tip: Learn precise scientific keywords for each separation technique, such as 'insoluble', 'vaporization', and 'condensation'.

Question 2. Describe how you will be able to separate common salt from a mixture of ammonium chloride and common salt.
Answer: To separate a mixture of ammonium chloride and common salt, the property of sublimation is utilized:
1. Take the mixture in a china dish and place an inverted funnel over it, plugging the stem of the funnel with cotton.
2. Heat the china dish strongly using a burner.
3. Ammonium chloride sublimes directly from solid to vapor on heating and gets deposited on the cooler inner walls of the funnel.
4. Common salt does not sublime and is left behind as residue in the china dish.
In simple words: Heat the mixture so that ammonium chloride turns into vapor and sticks to the funnel, leaving common salt behind at the bottom.

Exam Tip: Mention sublimation explicitly, as it is the key principle for separating volatile solids from non-volatile solids.

Question 3. By giving two reasons prove that water is compound.
Answer: Water is considered a chemical compound because:
1. Fixed ratio: Water is composed of two elements, hydrogen and oxygen, combined in a fixed ratio of 2:1 by volume (or 1:8 by mass).
2. Loss of constituent properties: The properties of water (liquid at room temperature, extinguishes fire) are entirely different from the properties of its constituent elements, hydrogen (combustible gas) and oxygen (supporter of combustion).
In simple words: Water is a compound because it is made of hydrogen and oxygen in a fixed proportion, and its properties are totally different from those gases.

Exam Tip: Compounds always have fixed composition and entirely new properties compared to their constituent elements.

Question 4. Define sieving with an example.
Answer: Sieving is a mechanical method used to separate solid particles of different sizes by passing the mixture through a sieve (a utensil with a wire mesh or perforated bottom). Smaller particles pass through the holes of the sieve, while larger particles are retained on it.
Example: Separation of wheat bran (coarser particles) from wheat flour using a sieve.
In simple words: Sieving is like using a net to separate big particles from small particles, such as separating bran from flour.

Exam Tip: Always include both a clear definition and a household or laboratory example for process-based questions.

Question 5. How will you separate cream from milk?
Answer: Cream is separated from milk using a process called centrifugation. Milk is placed in a centrifuge machine and spun rapidly. Because cream is less dense than the skimmed milk, the rapid spinning forces the heavier milk components outward while the lighter cream stays towards the center, allowing them to be separated.
In simple words: Cream is separated from milk by spinning it very fast in a machine, which forces the heavier liquid outward and leaves the lighter cream separate.

Exam Tip: Mention 'centrifugation' and the difference in density as the underlying principle.

BIOLOGY

Question 1. Expand LPG and write a note on it.
Answer:
Expansion: Liquefied Petroleum Gas.
Note: LPG is a flammable mixture of hydrocarbon gases, primarily propane and butane. It is supplied as a liquid under pressure in steel cylinders. It is widely used as a fuel for heating appliances, cooking equipment, and vehicles. It burns cleanly, producing fewer greenhouse gas emissions compared to coal or oil, and leaves no soot behind.
In simple words: LPG stands for Liquefied Petroleum Gas, which is a clean-burning fuel stored in cylinders and used mainly for cooking.

Exam Tip: Memorize the expansion correctly and mention its main components (propane and butane) for full credit.

Question 2. What do you mean by energy crisis?
Answer: Energy crisis refers to any great bottleneck in the supply of energy resources to an economy, typically referring to the shortage, high cost, or depletion of fossil fuels (such as petroleum, coal, and natural gas) that power modern societies.
In simple words: Energy crisis is the shortage or severe rising cost of energy sources like coal and oil that we rely on.

Exam Tip: Tie energy crisis directly to the depletion of non-renewable fossil fuel resources.

Question 3. What are ores?
Answer: Ores are naturally occurring rocks or minerals from which a metal or valuable mineral can be extracted profitably.
In simple words: Ores are rocks containing minerals from which we can extract useful metals.

Exam Tip: Make sure to include the word 'profitably' in your definition, as not all mineral-bearing rocks are considered ores.

Question 4. Give examples of ores with the metals extracted from them.
Answer:

In simple words: Common ores include Bauxite for aluminium and Hematite for iron.

Exam Tip: Learn at least three standard ore-metal pairs thoroughly for chemistry and biology questions.

Question 5. What are gangue?
Answer: Gangue refers to the commercially valueless material (such as sand, rock, and earthy impurities) that surrounds, is mixed with, or is closely bound up with an ore in a deposit.
In simple words: Gangue is the unwanted rocky waste material mixed with extracted ores.

Exam Tip: Contrast 'gangue' (waste rock) with 'ore' (valuable mineral) in your mind to avoid confusion.