Grade 8 Science Unit 3: Forces and Fluids

Grade 8 Science Unit 3: Fluids & Viscosity - Chapter 9: Forces

• Forces influence the motion and properties of fluids.

Force

• Anything that causes a change in an object's motion.
• A push or a pull.

Balanced Forces

• Equal in strength.
• Opposite in direction.
• Result in no movement.
• Example: A person standing still on the Earth.

Unbalanced Forces

• Unequal in strength.
• Cause a change in speed or direction.
• Example: A child pushing down on one end of a seesaw.

Mass vs. Weight

• Mass:
  • Stays the same anywhere in the universe.
  • Measured in kilograms (kg).
• Weight:
  • A measure of the push or pull acting on an object.
  • Measured in Newtons (N).
• Weight varies based on the force of gravity. The same object weights differently on Earth, the moon and Jupiter.

Buoyancy

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

Density & Buoyancy

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

Average Density

• The total mass of all substances that make up an object divided by the total volume.

Technologies Developed (based on fluids principles)

• Personal flotation devices.
• Submarines.
• Hot air balloons.

Pressure

• The force acting on a certain area of a surface.
• The larger the force, the greater the pressure.
• The smaller the area, the greater the 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

• Provided example problems and solutions.

Determine Why

• Given specific examples: a person wearing snowshoes walking on deep snow and the variable flow of water coming out of a garden nozzle are studied.

Atmospheric Pressure

• Pressure exerted by the layers of air surrounding the Earth.
• Held by Earth's gravity (~160 km above Earth).

Pascal's Law

• Pressure applied to an enclosed fluid is transmitted equally throughout the entire container.
• Basis for hydraulic and pneumatic devices.

Hydraulics

• The study of pressure in liquids.
• Hydraulic systems are devices that transmit applied force through a liquid to move something else.
• Hydraulic systems use incompressible liquids.
• The pressure produced will exert in all directions equally.

Pneumatic Systems

• A gas is used to exert force on the gas in an enclosed space.
• Compressors are necessary as gases can be compressed to build up pressure.

Pressure & Volume

• Increasing pressure will decrease volume by the same amount.
• Known as Boyle's Law.

Temperature & Volume

• Increasing temperature will increase the volume of a fluid.

Temperature & Pressure

• Increasing temperature of a fluid will increase the pressure exerted.

Assignment

• Complete practice problems on pages 351-353.

Explore the essential principles of forces and their impact on fluids in this quiz based on Chapter 9 of Grade 8 Science. Understand concepts like balanced and unbalanced forces, as well as the difference between mass and weight. Test your knowledge on buoyancy and how these forces affect motion.