Density And Pressure
Visão Geral
Why does a sharp knife slice through food so easily while a blunt one just squashes it? Why can a small block of steel sink while an enormous steel ship floats? The answers lie in two quantities that connect force, area, mass and volume in surprisingly practical ways: density and pressure.
In this lesson you will learn how to calculate and measure density for regular and irregular objects, apply the pressure equation to explain everyday situations, and discover why pressure increases the deeper you go in a liquid. These ideas appear across both Papers 1 and 2 on the Edexcel International GCSE, often as structured calculation questions worth 3-4 marks.
Objetivos
- Know and use the relationship between density, mass and volume: density = mass / volume
- Investigate density using direct measurements of mass and volume
- Know and use the relationship between pressure, force and area: pressure = force / area
- Understand how the pressure at a point in a gas or liquid at rest acts equally in all directions
- Know and use the relationship for pressure difference: pressure difference = height x density x gravitational field strength, p = h x rho x g
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- A block has a mass of 500 g and a volume of 200 cm3. What is its density? A) 0.4 g/cm3 B) 2.5 g/cm3 C) 100 g/cm3 D) 2500 g/cm3 Answer: B
- Which method is used to find the volume of an irregularly shaped solid? A) Using a ruler to measure dimensions B) Placing it on a balance C) Using a displacement can and measuring cylinder D) Heating it until it melts Answer: C
- A force of 200 N acts on an area of 0.5 m2. What is the pressure? A) 100 Pa B) 200 Pa C) 400 Pa D) 1000 Pa Answer: C
- At a point in a liquid at rest, pressure acts: A) Only downward B) Only upward C) Equally in all directions D) Only sideways Answer: C
- Which change would increase the pressure at the bottom of a container of liquid? A) Using a wider container B) Using a shorter container C) Using a denser liquid D) Reducing the gravitational field strength Answer: C
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Secção do manual
Density
Which weighs more, a ton of feathers or a ton of bricks? This old riddle plays with the distinction between mass and density. A ton is a ton, of course; but bricks have much greater density than feathers, and so we are tempted to think of them as heavier. (See Figure 11.4 .) Density , as you will se
"College Physics: Density" by OpenStax, OpenStax, Rice University, licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Source: https://openstax.org/books/college-physics/pages/11-2-density. Access for free at https://openstax.org/books/college-physics/pages/1-introduction
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Pressure
You have no doubt heard the word pressure being used in relation to blood (high or low blood pressure) and in relation to the weather (high- and low-pressure weather systems). These are only two of many examples of pressures in fluids. Pressure P P size 12{P} {} is defined as where F F size 12{P} {}
"College Physics: Pressure" by OpenStax, OpenStax, Rice University, licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Source: https://openstax.org/books/college-physics/pages/11-3-pressure. Access for free at https://openstax.org/books/college-physics/pages/1-introduction
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