# Density and pressure

> Grade 9: density = mass / volume, why things float or sink, pressure = force / area, pressure in liquids increases with depth, air pressure.

Source: https://olyclass.com/library/science-g9-density-pressure-en/

- Subject: Science
- Level: Grade 9
- Quiz: 16
- Play it free on one screen (projector, TV or whiteboard): https://olyclass.com/library?play=science-g9-density-pressure-en
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## Questions

1. Which formula gives density? (force ÷ area / mass × volume / mass ÷ volume / volume ÷ mass)
   Answer: mass ÷ volume
2. A block has a mass of 200 g and a volume of 50 cm³. What is its density? (0.25 g/cm³ / 10 g/cm³ / 150 g/cm³ / 4 g/cm³)
   Answer: 4 g/cm³
3. A metal has mass 90 g and volume 30 cm³. What is its density in g/cm³?
   Answer: 3 g/cm³
4. Two objects with the same volume but different masses have different densities.
   Answer: True
5. An object floats in water when its density is... (exactly double water's / less than water's density / more than water's density / the same as its mass)
   Answer: less than water's density
6. Water has a density of 1 g/cm³. Which material would sink in it? (Cork, 0.24 g/cm³ / Ice, 0.92 g/cm³ / Iron, 7.9 g/cm³ / Oil, 0.9 g/cm³)
   Answer: Iron, 7.9 g/cm³
7. A huge steel ship can float because its overall density is less than water's.
   Answer: True
8. Which formula gives pressure? (area ÷ force / force × area / force ÷ area / mass ÷ volume)
   Answer: force ÷ area
9. A force of 100 N acts on an area of 4 m². What is the pressure in N/m²?
   Answer: 25 N/m²
10. Why does a sharp knife cut better than a blunt one? (It has a larger contact area / It has a larger mass / Smaller area gives less pressure / Smaller area gives more pressure)
   Answer: Smaller area gives more pressure
11. Why do snowshoes stop you sinking into deep snow? (They concentrate force on a small area / They increase the force downward / They make you lighter / They spread your weight over a larger area)
   Answer: They spread your weight over a larger area
12. As a diver goes deeper in the sea, the water pressure on them... (decreases / drops to zero / increases / stays the same)
   Answer: increases
13. At the same depth, water pressure acts only downwards, not sideways.
   Answer: False
14. Why are dam walls built thicker at the bottom? (Water is lighter at the bottom / Water pressure is greatest at the bottom / Water pressure is greatest at the top / Water pressure is the same everywhere)
   Answer: Water pressure is greatest at the bottom
15. What causes air pressure? (Air particles colliding with surfaces / Air particles moving away from surfaces / Air particles sticking to surfaces / Wind blowing only in storms)
   Answer: Air particles colliding with surfaces
16. How does air pressure change as you climb a high mountain?
   Answer: It gets lower (decreases)