Grade 8 Science - Fluids and Viscosity

Fluids and Viscosity

• Grade 8 science unit
• Chapter 9: Forces influencing the motion and properties of fluids

Force

• Anything causing a change in an object's motion
• A push or a pull

Balanced Forces

• Equal in strength
• Opposite in direction
• No movement

Unbalanced Forces

• Unequal in strength
• Cause a change in speed or direction

Mass vs. Weight

• Mass: Stays the same everywhere in the universe, measured in kilograms (kg)
• Weight: A measure of the push or pull acting on an object, measured in Newtons (N)

Buoyancy

• The upward force on an object submerged in or floating on fluids
• An object that floats has neutral buoyancy
• The buoyant force equals the weight of the fluid that the object displaces

Density & Buoyancy

• If the density of an immersed object is greater than the density of the fluid, it will sink

Which Will Float? Why?

• Examples include comparing wooden boat vs. water-logged stick, metal block vs. metal boat, and sealed empty water bottle vs. full water bottle for analysis.

Average Density

• Total mass of all substances making up an object divided by the total volume

Technologies Developed

• Personal flotation devices
• Submarines
• Hot air balloons

Pressure

• Force acting on a certain area of surface
• Larger force = greater pressure
• Smaller area = greater pressure

Calculating Pressure

• The unit for pressure is the Pascal (Pa).
• Pressure can be determined if force and area are known.
• Formula: Pressure (P) = Force (F) / Area (A)

Sample Problems

• Problems and solutions regarding calculating pressure. Example problem: An aquarium with 10,000 N of water on a 1.6 m² base, what's the pressure? Answer: 6250 Pa.
• Another example problem: Atmospheric pressure (101,200 Pa) on a hand (0.006 m²) to calculate force. Answer: 607 N
• A third example problem: Glass with a 4.9 N weight of water exerting 1700 Pa pressure. What is the area of the glass's bottom? Answer 0.0029 m².

Determine Why

• Why snowshoes can walk on deep soft snow.
• Why a garden hose's nozzle can create fast/slow flow of water.

Atmospheric Pressure

• Pressure exerted by the air layers surrounding the Earth held by Earth's gravity (approximately 160 km above Earth)

Pascal's Law

• Pressure applied to an enclosed fluid transmitted throughout the container with equal force
• Basis for hydraulic and pneumatic devices

Hydraulics

• Study of pressure in liquids.
• Hydraulic systems transmit applied force through a liquid to move something else.

Pneumatic Systems

• Use gas to exert force on gas in an enclosed space
• Compressors are necessary as gases are compressible, used to build up air pressure.

Pressure & Volume - Boyle's Law

• Increasing pressure decreases volume by the same amount
• Pressure and volume are inversely related (Boyle's Law)

Temperature and Volume

• Increasing temperature increases the volume of a fluid

Temperature and Pressure

• Increasing temperature increases the pressure of a fluid

Test your knowledge of forces and the properties of fluids in this Grade 8 science quiz. Chapter 9 explores concepts such as balanced and unbalanced forces, buoyancy, and the differences between mass and weight. Challenge yourself with scenarios to determine what will float and why.