Grade 8 Science: Systems and Simple Machines

Flashcards covering the definitions of systems, simple machines, forces, work, power, and efficiency based on Grade 8 Science Lesson 1 through Lesson 8.

Physical system

A group of physical parts that work together to perform a function.

Mechanical system

A system that uses mechanical energy, such as a manual can opener or hand pump for water.

Optical system

A system that uses light energy, such as a camera or solar cell.

Hydraulic system

A system that uses water energy, such as a water wheel or rotating sprinkler.

Electrical system

A system that uses electrical energy, such as a flashlight or computer.

Subsystem

A smaller, simpler part of a larger system that can be further broken down into component parts.

Mechanism

A simple system that changes one type of force into another, such as a pedal and gear mechanism.

Input

The force, energy, or raw materials that are put into a system.

Output

The task or service that a system performs.

Simple machines

Devices that are made up of only one or two parts and require a single force to work.

Inclined plane

A tilted surface where moving a load requires more distance travelled but less effort.

Wedge

An inclined plane that can be moved to force objects apart, such as a door stop or axe.

Screw

An inclined plane wrapped around a central core.

Lever

A rigid bar that pivots on a fulcrum.

Fulcrum

The pivot point of a lever.

Load arm

The part of a lever that extends from the fulcrum to the load being moved.

Effort arm

The part of a lever that extends from the fulcrum to where the force is applied.

Input force

The force applied by a user to operate a lever.

Output force

The force that ends up moving the object in a system.

First Class Lever

A lever where the fulcrum is located in between the input force (effort) and output force (load), such as a teeter-totter.

Second Class Lever

A lever where the load is located in between the effort force and the fulcrum, such as a wheelbarrow.

Third Class Lever

A lever where the effort force is located in between the load and the fulcrum, such as a fishing rod.

Wheel and Axel

A simple machine consisting of a large circle (wheel) and a rod it is attached to (axel).

Gear

A wheel component with teeth that intermesh with another wheel.

Pulley

A machine consisting of a wheel or set of wheels and a rope or set of ropes.

Force

An interaction that can change the motion of an object.

Magnitude

How strong a force is.

Direction

The way that a force is pushing or pulling.

Vectors

Arrows that represent forces, indicating both a magnitude and a direction.

Newtons ($N$)

The unit used to measure force, named after Sir Isaac Newton.

Mass

A measure of the amount of matter in an object.

Weight

A measure of how strong the force of gravity is on an object.

Friction

The force that resists the motion between two objects that are in contact.

Static friction

The force that holds a stationary object in place.

Sliding friction

The force that acts like a brake when one surface moves across another.

Lubricants

Materials used between two surfaces in contact to reduce friction, heat build-up, and wear on parts.

Mechanical advantage ($MA$)

The ratio of output force to the input force for a given machine.

Work ($W$)

Performed when force is applied and an object is moved a distance; measured in Joules ($J$).

Energy

The ability to do work; measured in Joules ($J$).

Power ($P$)

Work done divided by time; measured in Watts ($W$).

Mechanical efficiency ($ME$)

The percentage of work input that is turned into useful work output.

eight types of forces

gravitational

magnetic

electrical

mechanical

frictional

tensile

compressive

rotational