StructuresandMechanisms

Structure or Mechanism?

Can you identify a Structure within this bicycle?

Can you name a mechanisms on this bicycle?

Frame = Structure

Chain and Sprocket = One example of a mechanism

Introduction

Vehicle Frame

High Rise Building

Bridge Supporting Roadway

Residential Dwelling

Structures can be seen all around us in our everyday lives.

Introduction

Machinery is a central part

of life today.

How many can you

identify?

Drill Tractor

Car Luas Exercise Bicycle

Introduction

Rack and Pinion Pulley WheelsCam and Follower

All these machines have working parts called –Mechanisms

Introduction Look at the following items.

1. Bicycle 2. Wheelbarrow

3. Wrench

Can you identify and name the mechanisms and/or structure in each of these items?

4. Entrance

Mechanisms, Motion and Force

Mechanism

A system of moving parts that performs some function.

Motion The process of continual

change in the position of an object “movement”

Collins Dictionary

Collins Dictionary

Motion and Force

What input is needed for a drill to work?

Input: The lever of the drill is pulled down

Output: The chuck of the drill moves down

Exertion or the use of exertion against a person or thing that resists.

Collins Dictionary

Force “Strength or Power”

Motion There are four main types of motion.

Linear motion – Train

Oscillating Motion – Pendulum of a clock

Reciprocating Motion – Hacksaw

Rotary Motion - Shaft

Pendulum

Train

Shaft

Motion Linear motion

– movement in a straight line

A train on its tracks moves in a linear motion

Can you give other examples of linear motion?

Motion Reciprocating Motion

- backwards and forwards movement

The engine pistons and valves above move up and down (reciprocate) continuously.

Can you suggest other examples?

Motion

Oscillating Motion

Forward and backward movement in an arc

The pendulum of a clock or a child on a swing

are examples of oscillating motion.

Rotary Motion

- Motion in a circular direction, which can also be called circular motion .

The wheels of a bike move in a rotary fashion.

ForceThere are five main types of force:

1. Compression

2. Tension

3. Shear

4. Bending

5. Torsion Columns in

Compression

A rope in Tension

Pipe Bending

Torsion forces

Shear forces

ForceCompressive and Tensile Forces

Spring in Tension, this is where a load pulls an object apart.

This is where a load presses or squashes objects together

Can crushed by compression

Force

This is where loads push at right angles to the surface of the object. E.g. scissors

Torsion and Shearing forcesShearing Force

This is where the load

causes an object to twist

Torsion

Torsion force

Force

This is where the load causes an object to Bend

A piece of metal

Bending a piece of metal

Bending and Static Forces

Dynamic Load – a car which is not fixed to any one specific point, e.g. a car travelling along a road

Static Load – a load which is fixed at one point, e.g. a building