Fluids and Dynamics Unit 3 Science 8 Tannant

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

8.1 Forces A push or a pull Measured in NEWTONS (N)

Types of Forces Tension Force—when an object is pulled

Force of Friction Force going AGAINST movement. The rougher the surface the greater the friction.

Elastic Force Force exerted when a spring-like object restores to normal shape after being compressed or stretched.

Gravitational Force Force of attraction between objects because they have mass. Gravitational attraction increases the more mass the objects have. Gravitational attraction increases the closer objects are together.

Electrostatic Force Static Electricity Attraction between positive and negative charges.

Magnetic Force Iron, Nickel, Cobalt—can exert a pushing or pulling force (similar to both gravity and electrostatic force)

Mass and Weight Mass is the amount of particles in a substance (the amount of ‘stuff’) Weight = a measurement of the PULL OF GRAVITY on an object. – Measured in Newtons (force)

Newton The unit of force Measured using a spring scale (or force meter) 1 kgm/s 2 = 1 N

Balanced and Unbalanced Forces Objects move if ENOUGH force is applied to overcome the opposing forces.

Balanced Forces = No Movement

Net Force = Add opposing forces Net Force = 0

Unbalanced Forces = Movement

+ = Net Force = Movement

If the Force of Gravity > Force of Drag = Net Force  FALLING!

8.2 Pressure Pressure = the amount of force acting over a given area on an object.

As pressure is applied… Particles undergo COMPRESSION A decrease in volume produced by a force.

Pressure and Kinetic Energy Pressure in a fluid results from the particles colliding with the container walls. Pressure in fluids pushes out in all directions. The more energy in the fluid, the more collisions the particles (or the more particles present) have, the more PRESSURE there is.

More kinetic energy   Less kinetic energy

Compression in Gases, Liquids and Solids Gases have space between particles, so CAN be compressed easily. Liquid particles are very close together, so do NOT compress easily.

Solids don’t have enough space between particles, so do NOT compress at all.

Deformation A change of shape without being forced into a smaller volume. As an object deforms, it stores elastic energy  which helps the object return to its original shape.

Comparing Pressure Pressure is measured in a unit called a pascal (Pa). [Very small amount!] 1000 Pa = 1 kPa (or kilopascal) kPa is the common measurement for pressure.

Also… Pressure is also measured in older units: Milimeters of Mercury (mmHg) in weather systems (barometers) Milibars (mb) for weather systems Pounds per square inch (p.s.i) in tires

Pressure Pressure (P) = force (F) – measured in N area (A) – measured in m 2 P = F/A

Calculating Pressure A large cement block is carried on the back of a pickup truck. The bottom of the cement block has dimensions of 8.5m by 4.0 m and it weighs 23,800 N. What pressure does it place on the truck?

Pressure increases in water

8.3 Viscosity, Adhesion, and Cohesion

Viscosity The resistance of a fluid to flow. – How “thick” a fluid is at a specific temperature. – Measured by Flow Rate (cm/s)

The Effect of Temperature on Viscosity

Liquids Heated  Particles move further apart  Less attraction between particles  Less friction  Viscosity decreases Cooled  Particles move closer together  Increased attraction between particles  More Friction  Viscosity Increases

Gases Heated  Particles move further apart  Particles move faster  More collisions, so more friction  Viscosity INCREASES Cooled  Particles move closer together  Particles move slower  Less collisions, so LESS friction  Viscosity DECREASES

Adhesion The attraction (joining) of two different objects or fluids to each other. – “Sticky-ness” – Example: water has a high adhesion to glass. – Polarity (or slight charge) causes this. Polar molecules like other polar molecules.

Adhesion

Non-polar molecules like other non- polar molecules Example: oil and butter in cooking

Polar molecules HATE Non-polar molecules Oil and water

Cohesion The strength with which the particles of an object or fluid attract each other. (Attraction within the substance for itself) – Water molecules are highly attracted to other water molecules.

Surface Tension A property of a liquid in which the surface of the liquid acts like a thin skin or membrane.