5.5 Pressure & Pressure Differences in Fluids

• What is a fluid?

  A fluid is either a liquid or a gas
• How is pressure defined?

  Pressure is the force per unit area

  
• Why does a drawing pin penetrate a surface easily?

  Its sharp point creates larger pressure
• What effect do large tires on tractors have?

  They reduce pressure by spreading weight
• Why do nails have sharp pointed ends?

  To create large pressure over a small area
• What happens when an object is immersed in a liquid?

  The liquid exerts pressure, squeezing the object
• How do forces act on surfaces in fluids?

  Forces act at right angles to the surface
• What units is pressure measured in?

  Pressure is measured in Pascals (Pa)
• What area should be used to calculate pressure?

  The cross-sectional area of the object
• What does spreading force over a large area result in?

  It results in small pressure
• Why do high heels produce higher pressure?

  They have a smaller area compared to flats

  
• What is the pressure created by a pump in a lifting machine?

  5.28 × 10⁵ Pa
• How do you calculate force from pressure and area?

  F = p × A

  
• What is the calculated force applied to the piston?

  14,400 N or 14.4 kN
• What is the atmospheric pressure at sea level?

  About 100 kPa
• How does atmospheric pressure change with altitude?

  It decreases with increasing altitude

  
• What causes atmospheric pressure?

  Air molecules colliding with a surface

  
• What happens to air molecules as altitude increases?

  The number of air molecules decreases

  
• What is the relationship between pressure and density of air?

  Pressure decreases as density decreases
• How does pressure in a liquid change with depth?

  Pressure increases with the height of the liquid column
• What causes pressure in a liquid?

  The weight of the liquid pushing against objects
• Where is the highest pressure in a column of water?

  At the bottom of the column
• What is the equation for calculating pressure in a liquid?

  p = h × ρ × g

  
• What does upthrust refer to?

  It is a force pushing upwards on an object
• What determines the size of upthrust?

  The density of the fluid and displaced volume
• Why do boats float?

  Because upthrust is greater than their weight
• What causes upthrust in a submerged object?

  The difference in pressure between top and bottom
• What happens if an object's density is less than the fluid's density?

  The object will float
• What happens if an object's density is greater than the fluid's density?

  The object will sink
• Why does a polystyrene block float in water?

  It has a density less than water
• Why does a wooden block float partially submerged?

  Its density is slightly less than water
• Why does an iron block sink in water?

  It has a density much higher than water