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Exploring the Investigative World of Science - Probe and ponder

Grade 8CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Scientific Investigation: A systematic process involving observation, forming a hypothesis, conducting experiments, and drawing conclusions to understand the natural world.

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Physical Quantities: These are properties that can be measured, consisting of a numerical value and a unit (e.g., length LL, mass MM, and time TT).

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Measurement of Volume: For regular solids, volume is calculated using dimensions. For irregular solids, the water displacement method is used where Volume of object=Vfinal−Vinitial\text{Volume of object} = V_{final} - V_{initial}.

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Density: It is defined as the mass of a substance per unit volume. It determines whether an object will sink or float in a fluid. The formula is ρ=mV\rho = \frac{m}{V}.

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Pressure: The perpendicular force (thrust) acting on a unit area of a surface. The SI unit of pressure is the Pascal (PaPa), where 1 Pa=1 N/m21 \text{ Pa} = 1 \text{ N/m}^2.

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Variables in Experiments: The 'Independent Variable' is the factor changed by the investigator; the 'Dependent Variable' is the factor being measured; and 'Controlled Variables' are kept constant to ensure a fair test.

📐Formulae

Density(ρ)=Mass(m)Volume(V)\text{Density} (\rho) = \frac{\text{Mass} (m)}{\text{Volume} (V)}

Pressure(P)=Force(F)Area(A)\text{Pressure} (P) = \frac{\text{Force} (F)}{\text{Area} (A)}

Volume of a Cuboid=l×b×h\text{Volume of a Cuboid} = l \times b \times h

Average Speed=Total DistanceTotal Time\text{Average Speed} = \frac{\text{Total Distance}}{\text{Total Time}}

💡Examples

Problem 1:

A block of metal has a mass of 1200 kg1200 \text{ kg} and occupies a volume of 0.5 m30.5 \text{ m}^3. Calculate its density.

Solution:

ρ=1200 kg0.5 m3=2400 kg/m3\rho = \frac{1200 \text{ kg}}{0.5 \text{ m}^3} = 2400 \text{ kg/m}^3

Explanation:

Using the density formula ρ=mV\rho = \frac{m}{V}, we divide the mass by the volume to find the density in kg/m3\text{kg/m}^3.

Problem 2:

A force of 150 N150 \text{ N} is applied over an area of 3 m23 \text{ m}^2. Find the pressure exerted.

Solution:

P=150 N3 m2=50 PaP = \frac{150 \text{ N}}{3 \text{ m}^2} = 50 \text{ Pa}

Explanation:

Pressure is calculated by dividing the total force applied by the area over which it acts.

Problem 3:

A student is measuring the volume of an irregular stone using a graduated cylinder. The initial water level was 65 mL65 \text{ mL}. After submerging the stone, the level rose to 98 mL98 \text{ mL}. Calculate the volume of the stone using subtraction.

Solution:

98 mL−65 mL33 mL\begin{array}{r} 98 \text{ mL} \\ - 65 \text{ mL} \\ \hline 33 \text{ mL} \end{array}

Explanation:

The volume of the irregular object is the difference between the final volume and the initial volume of water.