Newton's Laws and Types of Mechanical Loads

Mechanics

Newton’s Three Laws of Motion

• An object remains at rest or in uniform motion unless acted upon by an external force (Inertia).
• Acceleration depends on the mass of an object and the force applied to it (F = ma).
• Every action has an equal and opposite reaction (Action-Reaction).

Branches of Mechanics

• Classical mechanics deals with the motion of everyday objects.
• An example of classical mechanics is Bernoulli’s Principle, which explains how objects like airplanes achieve flight.
• Quantum mechanics deals with atomic and subatomic particles.
• An example of quantum mechanics is heat transfer in a vacuum via quantum fluctuations.
• Relativistic mechanics deals with objects moving close to the speed of light.
• An example of relativistic mechanics is time dilation, where time slows down for a fast-moving object.

Loads

Types of Loads

• Static (Dead) Loads are constant loads due to a structure’s own weight.
• An example of a static load is the weight of an elevator itself.
• Live Loads are temporary loads due to external influences.
• An example of a live load is people in an elevator.
• Elisha Otis developed a safety mechanism to prevent elevator falls.
• Dynamic (Environmental) Loads are rapidly changing loads.
• Examples include dynamic loads like wind, rain, earthquakes, vehicles, and moving people.
• Earthquake-resistant buildings are an application of managing dynamic loads.

Stability

Centre of Gravity

• The point where gravity acts on an object, typically near its center.
• In humans, the center of gravity is near the pelvis, but it varies by height and weight.

Support for Stability

• Stability requires a strong support base to keep the center of gravity balanced.
• A chair’s legs create a stable base to prevent tipping.

States of Equilibrium

• Stable Equilibrium means an object remains upright when slightly displaced.
• A rocking chair is an example of stable equilibrium.
• Unstable Equilibrium means an object topples when slightly displaced.
• A football standing on its nose exemplifies unstable equilibrium.
• Neutral Equilibrium means an object moves but maintains its center of gravity.
• A rolling soccer ball demonstrates neutral equilibrium.

Example of Stability Issues

• The Leaning Tower of Pisa was not originally designed to tilt.
• The tower's instability was caused by unstable ground.
• Engineers adjusted the upper floors to compensate for the tilt.

Types of Structures

• There are three main types of structures: solid, shell, and frame structures.

Solid Structure

• Generally has no hollow spaces within it to avoid creating structural weaknesses.
• Strength comes from the bulk of its weight and structure.
• Dams serve as an example of solid structures.
• The strength of a dam is based on the materials used (usually concrete) and its thickness relative to the pressure exerted on it.

Shell Structure

• The arching of the shell structure is the root of its strength, distributing pressure away from the apex.
• Best used when greater pressure or force is expected that a solid structure alone cannot withstand.
• Roofing on buildings uses shell structures.
• Shell structures withstand the pressure of rain, snow, and other forms of precipitation.
• Shell structures create a domed ceiling, allowing for more volume inside the building.
• Six equilateral triangles can connect at a single vertex because each corner accounts for 60 degrees, totaling 360 degrees.

Frame Structure

• Frame Structures get their strength from the combination and configuration of parts that helps withstand forces
• Strength comes from the combination and configuration of parts that helps withstand forces.
• Goal-posts are an example of a frame structure.
• Each post cannot stand on its own.
• The rectangular formation of the posts creates stability and strength.
• The weakest element of a goal-post is the horizontal bar, which typically sags towards the ground.
• Triangular elements are utilized due to its strength at controlling tension and compression
• The upright triangle will create a stable base because of the width of the base
• The Load being placed on the triangle will create stress on the two non-base sides in the form of Compression
• The Base will incur Tension as it tries to support the compressed sides

Trusses

• Frames structures that try to take advantage of triangular formations are called Trusses
• Trusses are made by continuously link triangles which will distribute the tensile and compressive forces throughout the structure
• Segmenting a triangular formation into smaller triangles can strengthen the larger triangles.
• Gussets are reinforcements placed at the joint where triangles meet to further resist tensile and compressive forces.

Ties and Struts

• Ties and struts are structures that can be added to a preexisting structure to help strengthen it against forces
• A tie is a support structure that can help resist tension.
• A strut is a support structure that can help resist compression.

Arches

• Arches in structures have to resist compressive forces that are placed on the structure
• Arches have the main responsibility to resist compressive forces that are placed on the structure
• The keystone helps to distribute the force through the arch.
• The springer is the end point of the arch that will transfer the force to a foundation.

Types of Bridges

• There are five main types of bridges, each with its own ways of dealing with forces of tension and compression.
• The Confederation Bridge is roughly 13 kilometers and takes about 10 minutes to cross at 80 km/h.
• The Confederation Bridge connects Prince Edward Island to New Brunswick and was completed in 1997.

Beam Bridge

• Composed of beams that are held up on either end, and usually have columns to create support.
• Basic bridges balance tensile and compressive forces.

Truss Bridge

• Similar to beam bridges.
• Truss bridges use additional components to help shoulder more weight compared to a beam bridge.

Arch Bridge

• Arch Bridge is basically a beam bridge that has an arch support which resists compressive forces that are transferred to strong foundations

Suspension Bridge

• Allows for the tensile forces to be transferred to columns supporting the bridge
• The suspension cables help resist the compressive forces.

Cantilever Bridge

• Is a modified version of a Truss bridge that allows for multiple components to withstand the tensile and compressive forces, but requires the ends to take on most of the weight
• Each segment or span of the bridge acts like a see-saw and needs the middle portion to create balance