Key Stage 3 (KS3) Physics Practice Test 2025 - Free KS3 Physics Practice Questions and Study Guide

Question: 1 / 400

What physical principle explains why helium balloons float?

Bernoulli's principle

Newton's third law

Archimedes' principle (buoyancy)

Helium balloons float due to Archimedes' principle, which relates to the concept of buoyancy. This principle states that any object submerged in a fluid experiences an upward force equal to the weight of the fluid that the object displaces. In the case of a helium balloon, the helium gas inside the balloon is less dense than the surrounding air. As a result, the weight of the air displaced by the balloon is greater than the weight of the balloon itself, including the helium inside it.

This imbalance of forces creates a net upward force, allowing the balloon to rise. The floating occurs until the balloon reaches an equilibrium point where the weight of the displaced air equals the weight of the balloon. This is a fundamental principle in fluid mechanics and provides clear insight into why helium-filled balloons ascend in the atmosphere.

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Pascal's principle

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