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unit 3: States of Matter

Liquids

Bernoulli's Principle

Liquids experience a number of forces:

1. Cohesion is the attraction between molecules of the same type.

The lateral (sideways) pressure exerted by a moving fluid decreases as the fluid's speed increases.

2. Adhesion is the attraction of molecules of a different type.

3. Surface tension

4. Capillarity

Solids

Gravitational pressure is caused by the pull of gravity on the mass of the liquid.

This is the principle at work which makes flight possible.

Two factors that affect gravitational pressure are the depth of the liquid and the density of the liquid.

Pressure in liquids

Pressure, force per unit area, is measured in units called Pascals. A Pascal is 1 newton per square meter.

P = F/A

Gases

There are 2 types of solids: crystalline solids and amorphous solids.

Lift is created when air flows more rapidly over the upper surface of a wing than the lower surface. Four factors affecting lift are:

Example 2 The small cylinder of a hydraulic press has an area of .0015 sq. m. If a force of 45N is applied to the small piston, what is the pressure within the larger cylinder?

Types of deformation

Hydraulics is the practical application of Pascal's principle.

Pascal's principle says that if pressure is applied to a fluid in a closed container the pressure is distributed equally throughout the container.

1. Lift is directly proportional to the square of the plane's speed.

A hydraulic device is any device that utilizes Pascal's principle to do work.

Boyle's Law - at a constant temperature, volume and pressure are inversely related.

Crystalline solids have an orderly arrangement of particles and have well-defined melting points.

2. Lift is directly proportional to the wing area.

A hydraulic device will multiply force at the expense of distance.

1. Stretching is the pulling apart of molecules or atoms. Hooke's law states that for small amounts of stretching, the amount of deformation is proportional to the force.

F = kx

properties of solids

Fi / Ai = Fo / Ao

Charles Law - at a constant pressure, volume and temperature are directly related.

3. Lift can be changed by changing the shape of the wing.

Kinetic Theory of Matter

Example 1 A certain spring has a constant of 500. N/m. How much force is needed to stretch the spring .0200 m?

Example 3 A hydraulic jack has a small piston with an area of .80 sq. cm and a large piston with an area of 60. sq cm. Calculate the output force if a force of 150 N is applied to the small piston.

4. Lift is increased by tilting the wing.

All molecules are in constant motion, and the faster the molecules move the warmer the object is.

2. Compression is the squeezing together of molecules or atoms (the opposite of stretching). Hooke's law also applies.

In liquids the molecules are able to move freely but remain close to each other, so cohesion is weaker.

Brownian motion is responsible for 2 other types of motion: Diffusion and Osmosis.

Solids experience deformation (a change in shape) when a force causes its particles to move out of position. Properties describing how solids respond to deformation are:

Amonton's Law - at a constant volume, temperature and pressure are directly related.

Amorphous solids have a random arrangement of particles and do not have specific melting points.

There is a direct relationship between the motion of the molecules of matter and the state of that matter.

3. Bending is a combination of stretching and compression. Hooke's law does not apply.

In gases the molecules are moving around rapidly, so cohesion is very weak.

Diffusion is the gradual mixing of molecules from an area of higher concentration to an area of lower concentration.

HARDNESS - the resistance to being marred.

Atoms or molecules of the same substance are held together by the force of cohesion. The faster the atoms or molecules are moving, the less they are affected by cohesion.

Liquid and gas molecules experience random motion called Brownian motion.

4. Shear occurs when two forces act in opposite directions, side by side.

There are 2 hardness scales:

1. Mohs scale measures the ability to be scratched. Talc has a hardness number of 1 because it is very easily scratched, but a diamond has the highest hardness number of 10.

Osmosis is diffusion through a semipermeable membrane.

2. Brinell's scale measures how easily a material is dented by a hard ball.

Pressure in gases

In solids the atoms or molecules only vibrate in fixed positions, so cohesion is very strong.

5. Torsion is a twisting force (shear in a circle).

Atmospheric pressure is caused by the pull of gravity on air. It is measured by using a barometer.

Fluid Displacement

ELASTICITY - the ability of a solid to recover to its original shape after being deformed.

There are two types of barometers: mercury and aneroid barometers.

Two other properties related to elasticity are:

Archimedes' principle is the principle behind buoyancy. It states that the buoyant force of an object is exactly equal to the weight of the displaced fluid.

PLASTICITY - the maximum amount of deformation a solid can experience without breaking.

RESILIENCE - how far a solid can be deformed before the deformation becomes permanent.

Some solids (like gold) are very plastic, while others (like glass) are not plastic.

Objects float because they weigh less than the weight of a displaced fluid.

RIGIDITY - how strongly a solid resists being deformed.

Plasticity can be increased by heating the solid. This is especially true for amorphous solids.

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