Fluids are Affected by Forces, Pressure and Heat Chapter 8 Fluids are Affected by Forces, Pressure and Heat

8.1 Forces 2 Groups of Forces Force= push or pull that acts on an object 2 Groups of Forces Contact Forces = only have an effect on objects they touch Action-at-a-Distance Forces = can apply forces to an object without touching it

Contact Forces Tension Force – force experienced by a wire or rope when pulled at both ends Friction Force – works to slow down or stop motion due to surfaces rubbing together Elastic Force – exerted when a spring-like object restores itself to normal shape

Action-at-a-Distance Forces Gravitational Force – force of attraction between objects due to mass (depends on mass and distance of objects) Electrostatic Force – static electricity = the excess of positive or negative charge, causes pushing and pulling forces (Like charges repel Opposite charges attract) Magnetic Forces – Natural magnets, electromagnets, and the Earth exert pushing or pulling forces on certain metals (iron, nickel, cobalt)

Measuring Mass Mass is measured in metric units (grams, kilograms) Measured using a balance scale Mass is the same anywhere in the universe

Weight Depends on Gravity Weight is the amount of force on an object due to gravity Bathroom scales actually measure force not mass

The Newton Force is measured in Newtons (N) (Sir Isaac Newton) It is a small amount of force about enough to hold up an apple Weight is measured in Newtons because weight is a force

Measuring Force Use a force meter to measure (the most common type = spring scale) Mass and weight are directly proportional but not the same thing! If you change one it affects the other. To convert mass to weight multiply by 9.8 meter/second squared

Forces and Motion Balanced Forces - equal in strength and opposite in direction Sometimes keep an object stationary or in motion Unbalanced Forces – cause a change in speed/direction of an object Arrows are used to show direction of the force

Homework Textbook Questions! Page 289 Questions # 2-4, 6 Complete your Ch. 8 vocab. Quiz next class!

8.2 Pressure Pressure = the amount of force acting over a given area on an object Compression = decrease in volume produced by a force

Gases Are Compressible Gases are easy to compress due to the space between their atoms Less than 1% is actually the particles in a gas Need a container and a force to create compressed gas (air compressor)

Pressure and Kinetic Activity in Gases Pressure is a good indicator of kinetic energy of a gas Heat added increases the pressure can cause explosions or implosions

Liquids and Solids are Very Difficult to Compress Particles of solids and liquids are tightly packed so compression does not occur using normal means (incompressible)

Compression and Deformation Deformation = change in shape without being forced into a smaller volume Examples - Styrofoam cups, bouncing a ball The air inside is being compressed

Comparing Pressure Spreading force over a greater area means the pressure can be reduced (bed of nails) We use the formula: Force (measured in Newtons (N) Area (measured in m2)

Calculating Pressure A BMX rider exerts a force of 1200N on a sheet of plywood that measures 1m x 2m. How much pressure is exerted? P= F/A P = 1200N/(1mx2m) P = 600 N/m2 = 600 Pa

Page 296 Practice Problems 1-3 Homework Questions Textbook Questions Page 296 Practice Problems 1-3 Page 299 Questions # 2,3,5,6

8.3 Viscosity, Adhesion, and Cohesion Viscosity = the resistance of a fluid to flow, the slower it flows the more viscose the liquid is Due to the: Particles in some liquids flow past each other better than others Some particles have greater attraction to each other Oil = complicated molecule ; water = simple molecule

Flow Rate of Various Liquids You can compare liquids by measuring their flow rates = speed at which a fluid flows from one point to another

Effect of Temperature on Viscosity Size and shape of liquid particles and the attraction between particles contribute to friction Liquids Heated = viscosity decreases Cooled = viscosity increases Gases Heated = viscosity increases Cooled = viscosity decreases (less friction) Liquids and Gases are opposite!!!

Adhesion Another property of fluids that can affect their flow is adhesion Adhesion = attraction or joining of two different objects or fluids to each other Fluids are sometimes attracted to surfaces Example : water molecules have polarity which means one end of the molecule is positive and the other is negative – makes the molecule sticky It is hard to get all water out of a cup

Cohesion Cohesion = strength with which the particles of an object or fluid attract each other • Water molecules attract one another at the surface creating surface tension • Example: water strider insects

Homework Questions Textbook Questions Page 309 Questions# 1,3,4,5,6