Pressure & Buoyant Forces — Drills · Grade 8 Science

Chapter: Forces

What these drills covers

By the end of Pressure & Buoyant Forces you should be able to:

6 questions, written answer, numeric and multiple choice, each with a worked explanation.

Vocabulary used: pressure, fluid, buoyant force, model, evidence, system boundary, assumption.

Problem 1

Which has greater water pressure: 1 m or 3 m below the surface?
Answer and explanation

3 m, because liquid pressure increases with depth.

Problem 2

A 10 N force is spread over 2 m². Find the pressure.
Answer and explanation

5 Pa

10 ÷ 2 = 5 N/m² = 5 Pa.

Problem 3

A force of 200 N acts on an area of 4 m². What is the pressure in pascals?
Answer and explanation

50 Pa

pressure = force/area = 200/4 = 50 Pa.

Problem 4

What force in newtons produces a pressure of 300 Pa on an area of 0.2 m²?
Answer and explanation

60 N

force = pressure × area = 300 × 0.2 = 60 N.

Problem 5

Pressure in a liquid increases with
  1. depth
  2. width of the container
  3. colour
  4. surface area
Answer and explanation

depth

Greater depth means more fluid above, so greater pressure.

Problem 6

Explain why a heavy steel ship floats while a small steel bolt sinks.
Answer and explanation

Floating depends on average density, not on weight. The ship's hull encloses a large volume of air, so the ship as a whole is less dense than water and displaces enough water to support its weight. The solid bolt has no enclosed volume, so its density is that of steel, far greater than water, and it sinks.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

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