Science 8 unit D

Machines

help people use energy more efficiently

Lever

A rigid plank or bar that pivots around a fulcrum

First-class lever

A lever where the fulcrum is between the input and output forces (e.g., crowbar)

Second-class lever

A lever where the output force is between the fulcrum and the input force (e.g., wheelbarrow)

Third-class lever

A lever where the input force is between the fulcrum and the output force (e.g., fishing pole)

Inclined plane (ramp)

A surface that takes less force to move an object but requires the object to be moved over a longer distance

Wedge

An inclined plane used to split objects (e.g., axe, knife)

Pulley

A grooved wheel with a string, rope, or cord that helps to lift objects

Screw

An inclined plane wrapped around a cylinder (e.g., bolt, screw)

Wheel and axle

A system consisting of two circles of different diameters that rotate together (e.g., door knob, screwdriver)

Complex machine

A system of several simple machines working together to perform a function

Linkage

A mechanism that transfers force from one subsystem to another

Transmission

A special type of linkage that can change force, direction, and speed

Gears

Pairs of toothed wheels or cogs that interlock to transfer force and change speed

Driving gear

The gear that supplies the energy and turns the driven gear

Driven gear

The gear that turns as a result of the driving gear

Gear ratio

The ratio of the number of teeth on the driving gear to the number of teeth on the driven gear

How to calculate Mechanical Advantage (MA)

calculated by dividing Foutput/Finput

How to calculate Speed ratio (SR)

calculated by dividing input distance by output distance

How to calculate Efficiency

MA/SR x 100

Work

The product of force multiplied by distance, measured in joules (J)

Is a machine that has a mechanical advantage of less than one useful

Yes. It helps to control speed

Why do mechanical advantage and speed ration differ in real life?

Friction. SR is the ideal MA. Therefore friction does not affect SR

Iron

1. 1810. Hammer and chisel