Questions: Exploring forces

Q1. Define force and state its SI unit.

Answer (English): A force is the push or pull that appears when one object interacts with another. Its SI unit is the newton (N). A force can act through contact, as a hand does, or from a distance, as gravity does.

Hinglish: Force woh push ya pull hai jo kisi object par doosre object ke interaction se lagta hai. Iska SI unit newton (N) hai. Force contact se bhi lag sakti hai, jaise haath se, aur door se bhi, jaise gravity.

Q2. What changes can a force produce in an object?

Answer (English): A force can make an object move from rest, change the speed of a moving object, change the direction of its motion, or change its shape. Sometimes a single force causes more than one of these changes at once. For example, a bat hitting a moving ball changes both its speed and its direction, and pressing an inflated balloon changes its shape.

Hinglish: Force object ko rest se chala sakti hai, moving object ki speed badal sakti hai, uski direction badal sakti hai, ya uski shape badal sakti hai. Kabhi ek hi force kai changes ek saath karti hai. Jaise bat se ball maarna speed aur direction dono badalta hai, aur balloon dabane se shape badalti hai.

Q3. Explain the terms contact force and non-contact force with examples.

Answer (English): A contact force acts only when the objects touch, either directly or through something such as a rope or stick. Muscular force and friction are contact forces. A non-contact force acts without the objects touching. Magnetic force, electrostatic force and gravitational force are non-contact forces. The difference is the test: if the objects must touch for the force to act, it is a contact force.

Hinglish: Contact force tab lagti hai jab objects touch karte hain, seedha ya rope/stick ke through. Muscular force aur friction contact forces hain. Non-contact force bina touch ke lagti hai; magnetic, electrostatic aur gravitational forces non-contact hain. Simple test: agar force ke liye touch zaroori hai to contact force hai.

Q4. What is muscular force? Give two examples.

Answer (English): Muscular force is the force produced by the action of muscles, which contract and elongate during activity. Lifting a school bag and pushing a heavy box are examples. Animals use muscular force too: a horse pulls a carriage and bullocks plough a field. Inside the body, muscles help chew food, move it along the alimentary canal and keep the heart pumping.

Hinglish: Muscular force muscles ke action se banti hai, jo activity ke waqt contract aur elongate hoti hain. Bag uthana aur bhaari box dhakna iske examples hain. Janwar bhi muscular force use karte hain: ghoda carriage kheenchta hai aur bail khet jotate hain. Body ke andar muscles khana chabane, alimentary canal mein aage badhane aur heart pump karne mein help karte hain.

Q5. What is friction? On what does it depend, and in which direction does it act?

Answer (English): Friction is the resistance that appears when one surface slides, or tries to slide, across another. It arises because the minute irregularities of the two surfaces lock into each other. Friction always acts opposite to the direction of motion or attempted motion. It depends on the nature of the surfaces in contact: rough surfaces produce more friction than smooth ones. Fluids such as air and water also exert friction on objects moving through them.

Hinglish: Friction tab lagti hai jab object doosri surface par move karta hai ya move karne ki koshish karta hai. Ye surfaces ki chhoti irregularities ke aapas mein phansne se hoti hai. Friction hamesha motion ya motion ki koshish ke opposite direction mein lagti hai. Ye surfaces ki nature par depend karti hai: rough surfaces par zyada friction hoti hai. Hawa aur paani bhi moving objects par friction lagate hain.

Q6. What is magnetic force? How do like and unlike poles behave?

Answer (English): Magnetic force is the force a magnet exerts on another magnet or on a magnetic material. It acts without contact, so it is a non-contact force. When two magnets are brought close, poles that are alike (two norths or two souths) push apart, while a north facing a south pulls together. The ring-magnet activity shows this: with like poles facing, the upper magnet floats, pushed away by a magnetic force.

Hinglish: Magnetic force magnet ka force hai jo doosre magnet ya magnetic material par lagta hai. Ye bina contact ke lagta hai, isliye non-contact force hai. Do magnets paas laane par like poles (north-north ya south-south) repel karte hain, aur unlike poles (north-south) attract karte hain. Ring magnet activity mein like poles aamne-saamne ho to upar wala magnet float karta hai, kyunki magnetic force use dhakel deti hai.

Q7. What is electrostatic force? How do like and unlike charges behave?

Answer (English): When two materials are rubbed together, static charges build up on their surfaces. A charged object pulls on uncharged things made of particular materials, such as bits of paper. The force a charged body applies to another charged body, or to an uncharged one, is called electrostatic force, and it is a non-contact force. Like charges repel each other, while unlike charges attract. The two kinds of charge are called positive and negative.

Hinglish: Do materials ko rub karne par unki surface par static charges ban jaate hain. Charged object kuch uncharged cheezon ko, jaise paper ke tukdon ko, attract karta hai. Charged body ka doosri charged ya uncharged body par force electrostatic force hai, aur ye non-contact force hai. Like charges repel karte hain aur unlike charges attract karte hain. Do tarah ke charges hote hain: positive aur negative.

Q8. What is gravitational force? Describe the motion of an object thrown vertically upwards.

Answer (English): Gravitational force is the force with which the Earth pulls objects towards itself. It acts without contact and is always attractive. When an object is thrown vertically upwards, it moves up straight and slows down, stops for a moment at the top, and then falls straight down, speeding up as it descends. While going up its speed decreases, and while coming down its speed increases.

Hinglish: Gravitational force woh force hai jisse Earth objects ko apni taraf kheenchti hai. Ye bina contact ke lagti hai aur hamesha attractive hoti hai. Object ko seedha upar phenko to woh upar jaata hai aur slow hota hai, top par ek pal ke liye rukta hai, phir seedha neeche girta hai aur speed badhata hai. Upar jaate waqt speed kam hoti hai, neeche aate waqt badhti hai.

Q9. Differentiate between mass and weight.

Answer (English): Mass tells how much matter an object holds, measured in grams or kilograms, and it is the same everywhere. Weight is the gravitational pull of the Earth on the object, measured in newtons, and it changes with the strength of gravity. On the Moon an object has the same mass but about one-sixth of its Earth weight. Everyday speech often says a bag weighs 10 kg, but in science that number is its mass.

Hinglish: Mass object mein matter ki quantity hai, grams ya kilograms mein, aur har jagah same rehti hai. Weight woh gravitational force hai jisse Earth object ko kheenchti hai, newton mein, aur gravity ke hisaab se badal jaata hai. Moon par mass same rehta hai par weight Earth ka kareeb one-sixth ho jaata hai. Rozmarra mein "bag ka weight 10 kg" bolte hain, par science mein woh mass hai.

Q10. Why do some objects float and others sink? Explain with the idea of buoyant force.

Answer (English): A liquid pushes upward on an object placed in it, and this upward force is called upthrust or buoyant force. Gravity pulls the object down while the liquid pushes it up. When gravity wins, the object goes down; when the upward push matches gravity, the object stays on the surface. Archimedes' principle says the buoyant force matches the weight of the fluid pushed aside, so objects less dense than water, such as pumice, float.

Hinglish: Liquid mein rakhe object par paani upar ki taraf force lagata hai, jise upthrust ya buoyant force kehte hain. Gravity object ko neeche kheenchti hai aur liquid upar dhakelti hai. Agar gravity buoyant force se zyada ho to object doobta hai; agar dono barabar hon to tairta hai. Archimedes' principle kehta hai buoyant force utni hoti hai jitna displaced liquid ka weight hota hai, isliye paani se kam dense cheezein, jaise pumice, tairti hain.

The quick check below has five multiple choice questions on force, contact and non-contact forces, weight and mass. Each one comes with a short explanation, so take the quiz and see which topics need another read.