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Energy and Motion · Summer Term

Balanced and Unbalanced Forces

Students will understand how balanced and unbalanced forces affect an object's motion, leading to constant velocity or acceleration.

Key Questions

  1. Explain the relationship between unbalanced forces and acceleration.
  2. Compare the motion of an object under balanced versus unbalanced forces.
  3. Predict the direction of motion when multiple forces act on an object.

National Curriculum Attainment Targets

KS3: Science - Forces and Motion
Year: Year 8
Subject: Science
Unit: Energy and Motion
Period: Summer Term

About This Topic

Pressure in fluids explores how gases and liquids exert force over an area. Students investigate why pressure increases with depth in the ocean and decreases with altitude in the atmosphere. They also learn about upthrust and the conditions required for an object to float or sink, alongside the practical applications of hydraulics.

This topic meets the National Curriculum requirements for understanding atmospheric pressure and the effects of forces in fluids. It connects to both biology (breathing) and geography (weather). This topic comes alive when students can physically model the patterns of pressure using water columns and Cartesian divers to observe the effects of compressed air.

Active Learning Ideas

Watch Out for These Misconceptions

Common MisconceptionPressure only acts downwards.

What to Teach Instead

Students often think water only pushes down. Using a poked water bottle or a submerged ball helps them see that fluid pressure acts in all directions, which is why upthrust exists.

Common MisconceptionHeavy objects always sink.

What to Teach Instead

The classic 'steel ship' problem. Active investigations into density and displaced volume help students understand that floating depends on the relationship between weight and upthrust, not just total mass.

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Frequently Asked Questions

What is the formula for pressure?
Pressure is calculated by dividing the force applied by the area over which it is spread (Pressure = Force / Area). The standard unit for pressure is the Pascal (Pa) or Newtons per square meter (N/m2).
Why does pressure increase with depth in a liquid?
As you go deeper, there is a greater weight of liquid pressing down from above. This increased weight over the same area results in higher pressure, which is why deep-sea submersibles must have very thick hulls.
How do hydraulics work?
Hydraulics work because liquids are incompressible. When pressure is applied to a liquid in a closed system, that pressure is transmitted equally in all directions, allowing a small force to be multiplied into a much larger one.
What are the best hands-on strategies for teaching pressure?
Hands-on experiments like the 'crushing can' or using syringes to explore compressibility are vital. These activities provide immediate, visual evidence of atmospheric and fluid pressure that helps students overcome the counter-intuitive nature of invisible forces.

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