How Heavy How Light

What is weight? Weight tells us how heavy or light an object is. It is what we notice when we try to lift something or place it on a scale. In everyday life we describe objects as heavy (difficult to lift) or light (easy to lift).

How do we measure weight? We use measuring tools such as a balance scale (to compare two objects) and a spring (or digital) scale to find how many grams or kilograms an object weighs. For young learners, common units are grams (g) and kilograms (kg). A kilogram is 1000 grams.

Comparing weights: With a balance scale you put one object on each pan. If one pan goes down, that object is heavier. If both pans are level, the objects weigh the same. We also use numbers — e.g., 200 g is heavier than 50 g.

Useful ideas and tips: You can estimate weight by feeling and by comparing with known items (for example, a 1-litre bottle of water weighs about 1 kg). For classroom activities, sort objects into groups: light, medium and heavy. Use a kitchen scale for small items and a bathroom or luggage scale for heavier items.

Note on mass vs weight (simple): Mass is the amount of matter in an object; weight is how heavy the object feels because of gravity. For Class 4 it is enough to understand weight as how heavy something is and to measure it in grams and kilograms.

What is mass? Mass tells how much matter is in an object. In Class 4 we compare masses to say which object is heavier or lighter.

Units of mass: The two common units are kilogram (kg) and gram (g). 1 kg = 1000 g. Always use the same unit before comparing.

How to compare masses:

• Use a balance (pan or beam) — the side that goes down is heavier.
• If you have numbers, convert to the same unit and then compare: larger number = heavier.
• Use symbols: < means lighter than, > means heavier than, = means equal mass.

Ordering and difference:

• To order several masses, convert them to one unit (all grams or all kilograms) and arrange from smallest to largest (or reverse).
• To find how much heavier one object is than another, subtract: difference = |mass1 − mass2| (use the same unit).

Tips for students:

• Always check units and convert if needed before comparing.
• When using a balance, equal masses balance each other; add known weights to find an unknown mass.

What is mass? Mass is the amount of matter in an object. It tells how heavy or light something is. Mass is different from weight (weight depends on gravity), but in everyday use for Class 4 we use the word "weight" to mean mass.

Why do we need standard units? To compare and talk about mass clearly, everyone uses the same units. These are called standard units. In the metric system (SI), the standard unit of mass is the kilogram (kg).

Common metric units of mass:

• Gram (g) — used for light objects (a pencil, a fruit).
• Kilogram (kg) — used for heavier objects (a school bag, a person).
• Tonne (t) — used for very heavy things (a truck, a small vehicle). 1 tonne = 1000 kg.

Useful facts and conversions (these are important to remember):

• 1 kilogram (kg) = 1000 grams (g)
• 1 gram (g) = 1000 milligrams (mg)
• 1 tonne (t) = 1000 kilograms (kg)

How to choose a unit: Use grams for light objects (pieces of fruit, a pencil), kilograms for medium/heavy objects (bag, person), and tonnes for very heavy objects (vehicles, large machines). This makes numbers easy to read (for example, say 2 kg instead of 2000 g).

Measuring tools: We use balance scales, digital weighing machines or spring scales to find mass. The tool used depends on the object and how accurate we need to be.

Simple example of combining masses: If a bag of sugar is 3 kg and another packet is 500 g, convert to the same unit first. 500 g = 0.5 kg, so total = 3 kg + 0.5 kg = 3.5 kg (or 3500 g).

Tips for students:

• Always write the unit (g, kg, t) with the number.
• When adding or subtracting masses, convert to the same unit first.
• Memorize 1 kg = 1000 g — it is used very often.

What are kilograms and grams? Kilogram (kg) and gram (g) are units used to measure mass (how heavy something is). 1 kilogram is equal to 1000 grams. Kilograms are used for heavier things (like bags of rice), and grams are used for lighter things (like a pencil).

How to convert: Because 1 kg = 1000 g, you can convert between them by multiplying or dividing by 1000.

• Kilograms to grams: multiply the number of kilograms by 1000. Example: 2 kg = 2 × 1000 = 2000 g.
• Grams to kilograms: divide the number of grams by 1000. Example: 500 g = 500 ÷ 1000 = 0.5 kg.

Easy rules to remember: To change kg to g, add three zeros (or move the decimal point three places to the right). To change g to kg, move the decimal point three places to the left (or think of dividing by 1000).

Mixed units: Sometimes mass is given in kg and g together (for example, 3 kg 250 g). To convert mixed units to grams, convert the kilograms to grams and add: 3 kg 250 g = (3 × 1000) + 250 = 3250 g. To convert grams to mixed units, divide by 1000 to get kg and remainder grams: 3250 g = 3 kg 250 g.

What are weighing instruments? Weighing instruments are tools used to find how heavy (mass) an object is. Common instruments are the pan (balance) scale, beam balance, spring balance, and digital scale.

Units used: The usual units in Class 4 are grams (g) and kilograms (kg). Remember: 1 kg = 1000 g.

How to use different instruments:

• Pan (or beam) balance: Put the object on one pan and standard weights on the other pan. Add or remove standard weights until both pans are level. The total of the standard weights equals the object’s weight.
• Spring balance: Hang the object from the hook. The pointer moves and shows the weight on the scale. Read the value at the pointer.
• Digital scale: Place the object on the platform. Read the number on the display directly (it may show g or kg).

Important ideas to remember:

• Zeroing / Calibration: Make sure the scale reads zero before weighing (remove any extra weight or turn the scale to zero) so the reading is correct.
• Tare weight: If you weigh something in a container, first weigh the empty container (its tare). Subtract the container's weight from the total (gross) weight to get the net weight of the contents.
• Comparing weights: You can say one object is heavier, lighter, or equal in weight by using the balance or by comparing numbers shown by scales.
• Estimating: Before measuring, try to guess (estimate) which is heavier and then check with the instrument.

Reading and writing weights: When a scale shows kilograms and grams, write them like this: 2 kg 350 g. If you need only grams, convert: 2 kg 350 g = 2350 g. If you have only grams and want kilograms and grams, divide by 1000: 2350 g = 2 kg 350 g.

What are weights and units?
Weights tell us how heavy something is. In everyday use we measure weight in kilograms (kg) and grams (g). 1 kg = 1000 g.

Adding weights
To add two weights, add kilograms with kilograms and grams with grams. If the sum of grams is 1000 g or more, convert 1000 g into 1 kg and carry it to the kilogram column.

Steps (column method)

• Write kilograms in one column and grams in the next column.
• Add the grams. If grams ≥ 1000, subtract 1000 from that total and add 1 to the kilogram column.
• Add the kilograms (including any carry).
• Write the result as X kg Y g, where 0 ≤ Y < 1000.

Subtracting weights
To subtract, subtract kilograms from kilograms and grams from grams. If the grams in the minuend (top number) are less than grams in the subtrahend (bottom), borrow 1 kg (which equals 1000 g) from the kilogram column and add 1000 g to the grams column.

Steps for subtraction (column method)

• Write kilograms and grams in columns.
• If top grams < bottom grams, borrow 1 kg (1000 g) from the kilogram column and add to top grams.
• Now subtract grams and then subtract kilograms.
• Answer must be in the form X kg Y g with 0 ≤ Y < 1000.

Checking your answer
Add the answer and the subtracted weight; you should get the original weight (reverse operation).

Real-life uses: Buying fruits at the market, weighing ingredients for a recipe, checking luggage weight at the airport, measuring materials in a science project. These all use addition and subtraction of weights.

What is estimation of weight?
Estimation of weight means giving a sensible guess of how heavy an object is without using an exact measurement. It helps us make quick decisions in daily life.

Units used: Grams (g) for light things and kilograms (kg) for heavier things. 1 kg = 1000 g.

Why estimate?
Estimating is useful when you do not have a balance or need a quick idea — for shopping, packing bags, or checking if a load is too heavy.

How to estimate — step by step

• Choose a unit: grams for small items (e.g. an apple), kilograms for larger items (e.g. a sack of rice).
• Use known reference weights: compare with things whose weight you know (an apple ≈ 150 g, a textbook ≈ 500–700 g, a water bottle (1 L) ≈ 1 kg).
• Decide the level of rounding: nearest 100 g, nearest 500 g (half kg) or nearest 1 kg depending on how precise you need to be.
• Apply rounding rule: if the extra part is less than half the chosen unit, round down; if it is half or more, round up. (Example: to nearest 1 kg, 1.4 kg → 1 kg, 1.6 kg → 2 kg.)
• Check by adding or comparing: if you estimate many items, add their estimated weights to see if the total seems reasonable.

Tips for young learners

• Keep simple reference items at home (small stone = ~50 g, apple = ~150 g, book = ~500 g, bag of rice = 1 kg).
• When unsure, choose a coarser estimate (to nearest 100 g or 0.5 kg) rather than a false precise value.

What this topic means
Word problems about weight ask you to read short stories (situations), pick out the weights, decide which mathematical operation to use (add, subtract, multiply or divide), do any needed unit conversion (kilograms ↔ grams) and solve the problem. These problems use real-life situations like cooking, shopping, packing and measuring school supplies.

Steps to solve word problems

• Read the whole problem carefully and underline the weights and what is asked.
• Write the given data with units (kg or g). If units differ, convert them to the same unit.
• Decide the operation: add when combining weights, subtract to find how much is left or the difference, multiply for many equal items, divide for equal sharing or to find one item's weight.
• Perform the calculation, convert the answer to suitable units and check if the answer makes sense.

Common unit facts and tips

• 1 kilogram (kg) = 1000 grams (g). Always convert smaller to larger in a convenient way (e.g., change kg to g or g to kg) before adding or subtracting.
• Use the bar model or a number line to visualise addition/subtraction of weights.
• Estimate first to check the reasonableness of your answer (round weights to nearest 100 g or 1 kg).

Practical activities and experiments help you understand how to measure and compare the mass of objects. In the chapter "How Heavy? How Light?" we use simple tools such as a pan balance, a spring/kitchen scale and standard weights (grams and kilograms) to carry out experiments.

Follow these steps for any activity: plan (decide what to measure), collect materials (objects, balance/scale, standard weights, pencil and notebook), carry out the procedure (compare or measure), record observations in a table, draw conclusions and check results by repeating if needed.

• Use a pan balance to compare two objects directly: if one side goes down, that object is heavier.
• Use standard weights on a pan balance: add weights until the pans balance to find the mass.
• Use a kitchen or digital scale: place the object on the scale, zero (tare) it first, then read the mass.
• When measuring several items, add their masses to get the total mass. When comparing, subtract the lighter mass from the heavier to find the difference.

Important points: always note the units (g for grams, kg for kilograms), keep the scale on a flat surface, handle small weights carefully, and repeat measurements for accuracy.