Science Exam

Particle Theory of Matter

Matter is made up of tiny particles called *atoms and molecules...*

Each substance has *unique particles...*

Particles of matter are in *constant motion...*

Particles at a *higher temperatures move faster...*

Particles are *held together* by strong, attractive, electric forces...

Characteristic of Liquids

Fluids *do not have a definite shape* but take on the shape of their container...

Fluids can flow because the *particles of liquids and gases are free to move about...*

*Liquids and gases are fluids*

Liquids have *no definite shape* but *they have a definite volume...*

Gases have *no definite shape or definite volume* and *will completely fill the container they are placed in...*

Fluids can flow *through, around, and over different objects...*

Types of Flow

Laminar flow - When a liquid or gas travels smoothly in regular paths. (When fluids move in orderly lines across smooth pathways, allows fluids to move quicker and with more energy)

Turbulent flow - When a liquid or gas travels in irregular paths. (Turbulent flow adds oxygen to the water, Different currents, pathways, and objects can cause the water to become turbulent. e.g. plaque in blood vessels causes blood to have turbulent flow)

Taming Turbulence

Streamlined objects are shaped to reduce turbulence and create more laminar flow (For example wings on a plane and concrete linings)

Flow rate

A measure of how quickly fluids move, measured in *volume per unit of time.*

Surface Tension

The *strong attraction* among particles that form the surface of a liquid.

The particles are attracted to the other particles around them because the attractions are on the side and the bottom. These attractions are stronger and harder to break

Viscosity

A measure of how quickly the particles of a fluid can slide past one another...

Also called *thickness or resistance to flow...*

*More viscous liquids have stronger forces among the molecules and are harder to pour...*

*Less viscous liquids have weaker forces among the molecules and are easier to pour...*

When you *heat a liquid up* it becomes *less viscous* because *the particles have more energy* causing them to be *able to slide past one another more easily...*

When you *cool a liquid down* it becomes *more viscous* because *the particles have less energy* causing them to *have more resistance when sliding past one another...*

Cohesion

*The force of attraction between the particles of one substance...*

*A measure of how strongly the particles of a fluid attract each other...*

Adhesion

*The force of attraction between the particles of one substance...*

*A measure of how strongly the particles of a fluid attract each other...*

Methods of Changing Viscosity/Flow Rate

*Temperature...*

*The surface* that the fluid is flowing on...

*Force* pushing on the fluid...

What is Density?

Density is *a physical property of matter...*

*(Density \= Mass/Volume)*

What Does Density Look Like At A Particle Level?

*High-density objects* have *lots of particles packed* into the space...

*Low-density objects* have *fewer particles packed* into the space...

Formula for Density

The formula for density is mass divided by volume.

(g/cm3)

The density triangle is a way to find *density* with the given *mass and volume...* *(mass ÷ volume \= density)*

A way to find *volume* with the given *mass and density...* *(mass ÷ density \= volume)*

And a way to find *mass* with a given *volume and density* *(density x volume \= mass)*

Density and Water

*Water has a density of (1 g/ml)...*

If something is *denser than water* (having more than 1 g/ml) it will *sink...*

If something is *less dense than water* (having less than 1 g/ml) then it *floats...*

If something has the *same density as water, it stays where it was placed*. (e.g. if it is *placed at the bottom of a cup of water then it stays there* if it is *placed at the top it stays there* if it is *placed in the middle it stays there* etc...

What Is Buoyancy?

Buoyancy/buoyant force, is the *force exerted on an object immersed in a fluid.* *It determines whether an object floats or sinks...*

Buoyancy is *caused by differences in pressure acting on opposite sides of an object immersed in a static fluid...*

*Archimedes' principle* states that *the magnitude (size) of the buoyant force on an object is equal to the weight of the fluid it displaces...*

Factors that Affect Buoyancy

The *density of the fluid...*

The *volume of the fluid displaced...*

The local *acceleration due to gravity...*

Fluids Under Pressure

Compression is *the pushing and packing of the particles close together within a given amount of space...*

For *gasses particles are much more spread out and can be compressed more...*

For *liquids the particles are closer together, so they cannot be compressed as much as gases...*

Pneumatic System

Use *pressurized gases* to do things...

Safer to use as *gases can be compressed more...*

Hydraulic Systems

Use *pressurized liquids* (most often oil) to do work...

Used to lift heavy items and provide more precise movements...

Components of Fluid Systems

The *pump forces fluids through the system...*

*Conductors (Tubes or Pipes) provide a pathway to carry the fluid...*

Valves *keep the fluid moving in the desired direction at the desired time...*

The pressure gauge *monitors pressure within the system...*

Increasing and Decreasing Pressure

Increasing pressure is when *the force applied is transferred to a smaller point...* (For Example Thumbtacks)

Decreasing pressure is when *the force applied is spread over a larger area...* (For Example Snowshoes)

The formula for pressure is *force divided by the area of the part where the pressure is applied...*

Water and Atmospheric Pressure

Water pressure is the force exerted by water...

Water exerts pressure on all things underwater, it is much heavier than air...

Atmospheric pressure is the *force exerted by the atmosphere...*

*Atmospheric pressure decreases the higher you go up because there is less air pushing on you...*

Pascal's Law

When pressure is applied to a contained fluid (liquid or gas), *the force is transferred equally throughout the fluid in all directions...*

*The compressibility of different fluids affects how much pressure is transferred...*

Applying Pressure to Gas

*Applying pressure to gas in an enclosed area decreases its volume...*

Liquid's volume is also *decreased but not nearly as much as gas...* (can be slightly compressed)

Gas Tanks

When gas is compressed there are more collisions between its particles and the sides of the container...

If it is not made of a strong material like metal then the collisions could cause the tank to burst...

Metal is strong enough to withstand collisions...

*Gas tanks can explode when heated because the more heat causes more energy and more collisions which will eventually cause the tank to explode...*

How do Thermometers work?

*As the temperature increases the particles spread out more in the mercury* (red liquid) *causing an increase in volume...*

As the *temperature decreases particles come together and volume decreases...*

What is a Valve

*A mechanism that controls the flow of a fluid in a pipe...* (For example Sink taps)

Valves in the Circulatory System

The Circulatory System is *a closed hydraulic system...*

The heart pushes blood through arteries and veins...

*Veins have valves that help the blood to flow one way and not to flow backward...*

Some people have valves that do not work properly and the blood flows backwards. These are called *varicose veins...*

Internal Combustion Engine

A device that provides power by burning fuel in its cylinders...

The engine uses valves to allow fuel to enter the chamber and for exhaust gases to leave at the right time...

Power of Fluids

Heavy machines use hydraulic rams...

Like syringes, they have a piston inside the cylinder...

A pump pushes fluid into the cylinder causing the piston to move in or out with a large amount of force...

Powerful Hydraulics

Systems that use liquid...

Fire pumps and hoses cause water to leave with great force to spray far away...

Powerful Pneumatics

Systems that use gas...

Hovercrafts draw in air and drive it out under intense pressure below the craft providing a cushion for it to drive on...

Combination Systems

*Systems that use both gas and liquids...*

Car lift uses air to push oil out of a cylinder to drive a piston forward to lift a car...

Properties of Water

1. Polar Molecule

*Water molecules have a slight positive charge on the hydrogen side and a slight negative charge on the oxygen side...*

2. Cohesive

*Water molecules are attracted to each other.* This explains the spherical drop shape

3. Surface Tension

*The top layer of water molecules is extra cohesive and creates a skin-like surface...*

4. Adhesive