Density and pressure

Question 1

What is density, and what is its equation?

Answer 1

• Density is the mass per unit volume of a substance.
• The equation is: ρ = m / V
  
  • ρ = density (kg/m³)
  • m = mass (kg)
  • V = volume (m³)

Question 2

How can the density of a liquid be measured?

Answer 2

Method:
1. Measure the mass of an empty measuring cylinder.
2. Pour in a known volume of liquid and measure the new mass.
3. Subtract to find the mass of the liquid.
4. Record the volume from the measuring cylinder.
5. Use ρ = m / V to calculate density.

Question 3

How can the density of a solid be measured?

Answer 3

Method:
1. Measure the mass using a balance.
2. If the solid is regularly shaped, measure its dimensions and use a formula to find the volume.
3. If the solid is irregularly shaped, use a displacement can to measure the volume of water displaced.
4. Ensure the solid is fully submerged in the displacement can.
5. Read the volume from a measuring cylinder.
6. Use ρ = m / V to calculate density.

Question 4

What is pressure, and what is its equation?

Answer 4

• Pressure is the force per unit area.
• The equation is: P = F / A
  
  • P = pressure (Pascals, Pa)
  • F = force (N)
  • A = area (m²)

Question 5

Why does a bed of nails not hurt, but stepping on one nail does?

Answer 5

• The force (body weight) is the same in both cases.
• On a single nail, the area is small, so pressure is high, causing injury.
• On a bed of nails, the area is large, so pressure is lower, preventing injury.

Question 6

How does pressure act in a liquid or gas?

Answer 6

• In a fluid at rest, pressure acts equally in all directions.
• Pressure increases with depth in a liquid.
• Pressure creates a force at right angles to any surface it contacts.

Question 7

What is the equation for pressure difference in a liquid?

Answer 7

• The equation is: P = h ρ g
  
  • P = pressure difference (Pa)
  • h = height (m)
  • ρ = density of liquid (kg/m³)
  • g = gravitational field strength (N/kg, usually 9.8 N/kg)

Question 8

How can pressure in liquids be demonstrated?

Answer 8

Method:
- Use a container with holes at different heights.
- Observe that water flows faster from the lower holes due to higher pressure.
- This demonstrates that pressure increases with depth.
- Pressure acts equally in all directions at a given depth.