Starter quiz
- Which of the following is a definition of the density of an object?
- the volume per unit mass of the object
- the volume per unit weight of the object
- the mass per unit volume of the object ✓
- the weight per unit mass of the object
- the weight per unit volume of the object
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- Which of the following does the symbol represent?
- gravity
- weight
- gravitational force
- gravitational field strength ✓
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- Which of the following statements describe the movement and arrangement of particles in liquids?
- The particles are tightly packed. ✓
- The particles are widely spaced apart.
- The particles vibrate in fixed positions.
- The particles can move past each other. ✓
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- Which of the following statements are correct?
- If a fluid is compressed, its pressure increases. ✓
- A fluid only has pressure where it touches solid objects.
- A fluid that is not inside a container does not exert a pressure.
- At each point within a fluid, the pressure is equal in all directions. ✓
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- Which of the following explains why air pressure is lower at the top of a mountain than it is at the bottom of the mountain?
- The pressure in a fluid increases with depth. ✓
- The pressure in a fluid increases with height.
- The area of the mountain is larger at the bottom than at the top.
- The bottom of the mountain has more surface for the air to push on than the top.
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The picture shows a cross–section of a container of water. Which of the following statements about the pressure of the water is correct?- The pressure is greatest at the top of the water.
- The pressure is the same everywhere in the water.
- The pressure is the same at all places with equal depth. ✓
- The water exerts pressure on the bottom of the container but not on its sides.
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Exit quiz
- Which of the following statements explains why ice floats in liquid water?
- Ice is made of larger atoms than water.
- Ice is made of heavier particles than water.
- The particles move faster in water than in ice.
- The particles are farther apart in ice than in water. ✓
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- Which of the following statements correctly describe differences for particles of water at greater depths, compared with particles that are not as deep down?
- At greater depths, the particles are larger.
- At greater depths, the particles are heavier.
- At greater depths, the particles are closer together. ✓
- At greater depths, the particles push on each other with greater forces. ✓
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- Which of the following statements about upthrust is correct?
- Upthrust is caused by the weight of an object.
- Upthrust is caused by differences in pressure in a fluid. ✓
- No upthrust acts on an object that is floating on a liquid.
- No upthrust acts on an object resting on the bottom of a container of liquid.
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- For an object surrounded by a liquid, how many of the following are possible descriptions of the upthrust force: no upthrust; upwards upthrust; downwards upthrust; upthrust in all directions?
- none of them
- 1 ✓
- 2
- 3
- 4
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- A pupil places an object underwater and sees that it stays where it is, without floating upwards or sinking downwards. The weight of the object is 3 N. What is the upthrust force on the object?
- 0 N
- greater than 0 N but less than 3 N
- 3 N ✓
- greater than 3 N
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- A toy is dropped in a swimming pool. The toy has a mass of 0.80 kg, a weight of 8.0 N and an upthrust force of 6.0 N acting on it. What is the size and direction of the toy’s vertical acceleration?
- 2.0 m/s
- 2.5 m/s ✓
- 10 m/s
- upwards
- downwards ✓
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Worksheet
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Presentation
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Video
Lesson Details
Key learning points
- The pressure in a fluid increases with depth because the weight of fluid above pushes particles closer together.
- The pressure on an object in a fluid pushes with more force on the lower part of it and causes upthrust.
- An object floats in water if its density is less than that of water.
- The density of a material increases with the mass of each particle and the closeness of its particles.
- Ice is less dense than water as its crystal structure fixes the particles further apart than they are in water.
Common misconception
Pupils often do not understand that even sub–microscopic particles have a mass and volume, which affect the density of a substance.
Use the anomaly of ice floating on water to consolidate understanding that molecules have mass and that the spacing of water molecules can affect density.
Keywords
Pressure - produced by the forces from particles within a fluid acting on each other or on a surface
Particles - atoms or molecules that make up matter
Upthrust - a force acting upwards on an object in a liquid due to pressure differences between the top and bottom surface
Density - the mass per unit volume of a substance; a less dense substance will float on top of a more dense one
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