Science activity
Why Do Swimmers Shave and Wear Suits? Drag and Water
Discover that it is harder to move through water than through air.
Materials and setup
- bucket of water
- flat board or book
- cylindrical object
- notebook
How this changes by age
Pre-K (ages 3–4)
Discover that it is harder to move through water than through air.
Steps
- Wave your hand through the air. Easy!
- Now put your hand in a tub of water and wave it. Harder!
- Ask: Why is it harder to move through water? Water is thicker than air — it pushes back more.
- Swimmers have to push through water, so they try to make their bodies as smooth and straight as possible.
Learning objectives
- Observe that water creates more resistance than air
- Understand why smooth shapes move through water more easily
Kindergarten (ages 5–6)
Learn why swimmers try to make their bodies smooth and straight to go faster.
Steps
- Try this: push a flat book through a bucket of water, then push it edge-first. Which is easier?
- Explain: When you push the flat side, lots of water has to move out of the way. When you push the thin edge, much less water has to move.
- Swimmers try to make their body like the thin edge — streamlined.
- Ask: Why do you think swimmers wear special tight suits instead of baggy ones?
Learning objectives
- Understand that shape affects how easily an object moves through water
- Know that streamlined shapes reduce water resistance
Early elementary (ages 6–8)
Investigate drag and learn why streamlined shapes, smooth surfaces, and flat body positions help swimmers go faster.
Steps
- Learn the concept: Water resistance is called drag. Water is much denser than air — about 800 times harder to move through at the same speed.
- Test drag: push a flat board through water edge-first vs. face-first. Which takes more effort? Why?
- Discuss: Why do competitive swimmers wear tight suits (not baggy ones)? Why do they keep their body flat and horizontal? Why do they streamline (arms over head, feet together) when pushing off the wall?
- Research: What are high-tech swimsuits made of? Why did some get banned from competition?
- Write: 'Swimmers reduce drag by...'
Learning objectives
- Know that water is approximately 800 times denser than air
- Understand that streamlined shape, smooth surfaces, and flat position reduce drag
- Explain why high-tech suits were controversial in competitive swimming
Upper elementary (ages 8–10)
Apply the drag force equation and hydrodynamics concepts to analyze competitive swimming.
Steps
- Learn the drag force equation: F_drag = ½ × ρ × Cd × A × v², where ρ is fluid density, Cd is drag coefficient, A is frontal area, and v is velocity.
- Analyze each variable: Water density (ρ) is about 1000 kg/m³ vs. air (~1.2 kg/m³) — 800x greater. Swimmers reduce Cd by wearing smooth suits and shaving body hair. They reduce A (frontal area) by streamlining. Drag increases with the square of velocity — going twice as fast means 4x the drag.
- Research turbulent vs. laminar flow: Smooth suits promote laminar (smooth) flow. Rough surfaces create turbulent flow, which increases drag.
- Research the polyurethane suit controversy: Between 2008-2010, swimmers in polyurethane suits shattered world records at an unprecedented rate. FINA (swimming's governing body) banned them in 2010. Research why — what did the suits do to reduce drag?
- Michael Phelps won 23 Olympic gold medals — more than any athlete in history. Research his training approach and what techniques he used to minimize drag.
- Write: 'Hydrodynamics explains why competitive swimmers can win or lose by hundredths of a second because...'
Learning objectives
- Apply the drag force equation F = ½ρCdAv² to swimming
- Explain turbulent vs. laminar flow in the context of swimsuits
- Analyze the polyurethane suit controversy using fluid dynamics principles
- Know Michael Phelps' 23 Olympic gold medals as context
Safety and evidence note
Read the full activity before beginning. An adult should supervise tools, heat, food, outdoor work, movement, and experiments as appropriate. Completion records that the activity was done; the child’s explanation, work sample, photo, or demonstration is stronger evidence of learning than a completion check alone.
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