Thrust and Pressure

Discover why camels can run in deserts, why tanks have tracks, and why ships float while iron sinks!

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PHYSICS POSTER
BULLETIN BOARD
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HIGH PRESSURE
LOW PRESSURE
5 kg Block
40×20×10 cm
(Standing on 20×10 cm side)
5 kg Block
40×20×10 cm
(Lying on 40×20 cm side)

Given Data:

Mass = 5 kg
Dimensions = 40 cm × 20 cm × 10 cm
Weight (Thrust) = mg = 5 × 9.8 = 49 N

Case 1: Block on 20×10 cm side

Area = 20 × 10 = 200 cm² = 0.02 m²
Pressure = 49 N ÷ 0.02 m² = 2450 N/m²

Case 2: Block on 40×20 cm side

Area = 40 × 20 = 800 cm² = 0.08 m²
Pressure = 49 N ÷ 0.08 m² = 612.5 N/m²

Conclusion:

Same force on smaller area = Higher pressure
Same force on larger area = Lower pressure

Buoyant Force
Weight
Applied Force
Net Force
WATER

Iron Nail (Dense)

Density > Water → Sinks

Cork (Light)

Density < Water → Floats

Explore Thrust and Pressure
Pressure = Thrust ÷ Area
Thrust: Force acting perpendicular to a surface
Pressure: Thrust per unit area
SI Unit: Pascal (Pa) = N/m²
Key Point: Same force on smaller area creates higher pressure
Activity 9.4: Buoyancy Experiment
  • Take an empty plastic bottle with airtight stopper
  • Put it in a bucket filled with water - it floats
  • Push the bottle into water - feel the upward push
  • Try to push deeper - becomes more difficult
  • Release the bottle - it bounces back to surface
  • This upward force is called buoyant force or upthrust
Activity 9.5 & 9.6: Float or Sink?
  • Take a beaker filled with water
  • Place an iron nail on water surface - it sinks
  • Take a piece of cork and iron nail of equal mass
  • Place both on water surface
  • Cork floats (density < water), nail sinks (density > water)
  • Objects float when their density is less than the fluid
Why These Phenomena Occur?
🐪 Camel in desert: Large feet spread weight over bigger area → Less pressure on sand
🚛 Tank tracks: Distribute weight over large area → Less ground pressure
🚚 Wide tires: Larger contact area → Reduced pressure on road
🔪 Sharp tools: Small contact area → High pressure for cutting
🚢 Ships float: Large volume displaces water → Buoyant force > weight