Simple machines, Motion + structures, Materials + Plastics , Intros

Effort

A machine's input force that drives the movement

Load

A machine's output force that results from the movement

Fulcrum

The pivot point against which a lever is placed to get a purchase, or on which it turns or is supported.

Levers

A rigid bar that rotates around a fulcrum.

1st class lever

The fulcrum is between the effort and the load. (seesaw, scissor)

2nd class lever

The load is between the effort and fulcrum. (wheelbarrow, door)

3rd class lever

The effort is between the load and fulcrum.

(broom, fishing rod, tweezer)

How does fulcrums position impact effort?

The fulcrums position from the load determines the amount of effort needed. If fulcrum is closer to the load, less effort is needed to move the load. If fulcrum is closer to effort, the load will move a greater distance.

Velocity Ratio (VR)

VR = d1/d2

d1 - Distance of fulcrum(m) to effort d2 = distance of fulcrum to load (m)

Efficiency

The effectiveness of the machine, done by comparing MA and the VR.

How will an absence of friction or wear and tear, impact a machine?

The machine would have 100% efficiency (MA = VR)

Moments

A moment refers to the turning effect of a force around a fulcrum

Moments if a body is balanced (lever in equilibrium)

The total clockwise moment = the total anticlockwise moment (of the same point)

The sum of moments about the fulcrum is equal to 0.

Inclined plane

involves a plane surface inclined at a small

angle to the horizontal. It is used to lift a heavy mass up the plane by applying an effort along the plane

Pulleys

A pulley is a wheel with a grooved rim, or a combination of such wheels mounted in a block, for a cord or chain to run over for changing the direction or magnitude of a force, making it easier to lift a load.

What are the 3 types of pulleys?

Fixed, Moveable and compound

Fixed pulley

-Only one pulley/wheel fixed in place

-only redirect force (therefore no MA)

-make it easier to lift an object because you can pull down using weight to lift the object

What is the Ideal Mechanical Advantage of a fixed pulley?

IMA = 1

Moveable pulley (lifting pulleys)

-set of wheels and a rope

-lower pulley moves up when the rope is pulled =, creating a MA by reducing effort load

What is the Ideal Mechanical Advantage of a moveable pulley?

IMA = 2

Compound Pulley

Combines a fixed (not moving) pulley with a movable pulley (attached to the load)

When there is more than one pulley or wheel, lower pulleys move up when the rope is pulled and are called moving pulleys.

These combinations are called compound pulleys

What is the MA of Compound Pulleys?

MA = Number of Rope segments

IMA of Compound Pulleys(no friction) ?

MA = Load / Effort = W/F

Screws

A cylinder with a spiral groove around its outer surface, called the thread, use for conveying motion or bringing pressure to bear. The pitch is the distance between the threads.

Gears

A wheel with teeth that interlock or slot into others to create motion.

What are the advantages Gears can give?

Gears can give torque (force) or speed advantage

Torque

The term used instead of force when describing wheels and gears that rotate

Driving gear

Also called the driver, it is The gear that supplies energy. Sometimes a handle can be used to turn the driving gear.

Driven Gear

Also called the follower, it is the gear to which the force is directed.

Speed advantage in gears

When a large gear turns a smaller gear, turning the smaller wheel more times for the effort involved

Torque Advantage in gears

When a smaller gear turns a larger gear requiring less force to create a motion.

Idle gear

A gear added between the driver and driven gears to make them both go the same way (2 gears meshed together causes them to go opposite directions). The idler gear has no impact on the MA.

Gear Ratio > 1

Torque Advantage

Motion

The change of position of an object with respect to time

What are the 4 types of motion?

Linear, Rotary, Oscillating, Reciprocal

Linear motion

An object moving in a straight line

Rotary motion

An object moving in a circle or part of a circle (an arc)

Oscillating motion

Backward and forward motion in an arc

Reciprocal motion

Backward and forward motion in a straight line

How does a crank and piston change motion?

Rotating the crank makes the piston go back and forth in a reciprocating motion

How does a winch change motion?

Rotating the handle of a boat winch pulls the boat out of the water in a linear motion

What is the strongest shape for structures?

Triangles

How can triangles enhance a rectangle

A rectangle alone is unstable because lateral forces cause shear and joint rotation. Triangle braces transfer loads into axial compression, making the structure rigid.

How are domes strong?

Domes can resist compression however aren't usually used in modern construction due to its difficulty to construct and furnish

How are cylinders strong?

Cylinders have a curved shape that distributes force evenly around the surface, making it strong against compression

Bridges

Bridges must withstand many forces, and are often very high to allow ships to pass under (adding more stress to vertical supports).

What are the two types of bridges?

Cable-stayed and Truss bridges

Cable-stayed bridges

The main force acting on a cable-stayed bridge is gravity pushing down on the bridge and vehicles. Each stay (cable) is under tension, transferring the force to the towers, which are under compression force being pulled down from the stays above but supported by the ground, efficiently distributing the load and reducing bending in the deck.

Truss Bridges

A truss bridge uses triangles to distribute force on a bridge, with each part of the triangle under either compression or tension force.

3 main types of truss bridges

Warren, Pratt, Howe

Warren truss bridges

A Warren truss bridge uses a series of equilateral triangles, with members alternating between tension and compression, making it efficient for evenly distributed loads.

Pratt truss bridge

A Pratt truss bridge has diagonals that slope toward the center, carrying tension, while the verticals carry compression, making it efficient for heavy central loads.

Howe truss bridge

A Howe truss bridge has diagonals that slope away from the center, carrying compression, while the verticals carry tension, making it well suited for timber construction

Moments

Moment are the rotational or turning forces acting on an object.

Other names for moments

Torque or the moment of a force

What does a moment force produce?

A moment force produces a turning action that's clockwise (+ve) or anticlockwise (-ve). They are measured in Newton metres (Nm)

Moments in a balanced body

If a body is balanced, the total clockwise moment about a point equals the total anticlockwise moment about the same point.

Force in equilibrium

When 2 or more forces acting on an object and it remains at rest. (all forces acting on object are balanced)

Why is equilibrium important in engineering?

It is important because most constructions have to be build to withstand all foreign forces

Requirements for 2 forces in equilibrium

- Be equal in magnitude (size)

- Have lines of action which pass through the same point (i.e. concurrent)

- Act in exactly the opposite direction

Requirements for 3 forces in equilibrium

- they must all be on the same plane ( i.e. coplanar)

- Have lines of action which pass through the same point

(i.e. Concurrent)

-.When the forces are drawn head

to tail, then these lines form a

closed force triangle

Requirements for multiple forces in equilibrium

-ΣFx = 0 (horizontal forces are balanced)

-ΣFy = 0 (vertical forces are balanced)

-ΣM = 0 (moment forces are balanced)

What are the four main types of engineering?

Military, Civil, Chemical, Electrical

What is the problem solving process?

Explore, develop, Generate, evaluate

Simple Machine

A mechanical device that is used to make work easier and assist people by giving them a mechanical advantage.

Mechanical Advantage

A measure of the force amplification achieved by using a tool, mechanical device or machine system

What does a simple machine do

Create systems for different kinds of movement to occur when force is applied to a load. They are devised to amplify a force

What trade occurs in simple machines?

These devices which trade a small force over a large distance for a large force

over a small distance

Compound Machine

Combinations of two or more simple machines working together

What are the simple engineering machines?

Levers, Wheel and Axel, Inclined plane, Screw, Pulley, Wedge, Gears

What is Mechanical Advantage

Ratio of the effort load (input force) you put in, to the amount of force load (output force) put out

FL

Force Load or output force

FE

Force effort or input force

Force advantage (trade speed for force)

A machine makes it easier to move a heavy object but at a slower speed

Speed advantage (trade force for speed)

A machine makes the load go faster but with a weaker force

MA<1

No force advantage, distance advantage

MA>1

Force advantage

Newton 1st law

A body in motion remains in motion or a body at rest unless acted upon by a force

Newton 2nd law

Force (newtons) equals mass (kg) times acceleration (m/s²)

Newton 3rd law

For every action, there is an equal and opposite reaction

Weight

Force exerted on a body of matter due to gravity

Weight formula

Weight = Mass x Gravity

Force

The push or pull on an object (anything that causes an object, mass, to start moving)

What are the 5 types of forces that directly affect objects?

Compression, tension, shear, torsion, refraction

Compression (Axial)

A squashing force

Tension (axial)

A stretching force

Shear (Transverse)

Two forces pushing inwards but past each other

Torsion (Torsional)

A twisting force

Refraction

A bending force

Axial force

Acts along the member's axis

Transverse force

Acts perpendicular to the axis

Torsional Force

Acts around the axis, twisting the member

Engineering

Engineers are creators and problem solvers use science and maths to apply

Come up with ideas and applications to transform new realities in the world.

Work in industries like construction, transport, food, aerospace etc.

Gear Ratio < 1

Speed Advantage