Strand 3 Study Notes: Mechanical Systems (Machines, Power Transmission, Mechanisms, and Fluid Power)

Mechanical system

An arrangement of components that transmits and transforms motion, forces, and energy to do useful work.

Force

A push or pull that can accelerate an object.

Moment

The turning effect of a force about a point or axis.

Torque

Another term for moment, particularly in rotational systems.

Free-body diagram (FBD)

A diagram that isolates a component and shows all external forces and moments acting on it.

Static equilibrium

The condition when the sum of forces and moments acting on a component is zero.

Work

Energy transferred by a force acting through a distance.

Power

The rate of doing work.

Mechanical advantage (MA)

The ratio of output force to input force.

Velocity ratio

How output speed compares to input speed in a mechanical system.

Efficiency

The ratio of useful output power to input power.

Shear stress

The stress that occurs when a force is applied parallel to the surface of a material.

Torsional stress

The stress that occurs when torque is applied to a shaft.

Bearing

A component that supports a rotating shaft and allows it to turn with minimal friction.

Key

A removable piece that locks a hub to a shaft.

Spline

A set of ridges and grooves that distribute torque around the circumference.

Coupling

A device used to connect two shafts to transmit torque.

Gas laws

Equations that describe the behavior of gases under various conditions.

Slip

The relative motion that occurs between two surfaces in contact when friction is insufficient to hold them together.

Damping

The process of reducing the amplitude of vibrations.

Natural frequency

The frequency at which a system tends to oscillate in the absence of any driving force.

Resonance

A phenomenon that occurs when a system is subjected to a periodic driving force at a frequency close to its natural frequency.

Kinematics

The branch of mechanics that deals with motion without considering the forces that cause it.

Dynamics

The study of forces and their effect on motion.

Four-bar linkage

A mechanism consisting of four links and four joints that forms a closed-loop system.

Crank-slider mechanism

A mechanism that converts circular motion into linear motion.

Hydraulics

The use of liquid fluid power to perform work.

Pneumatics

The use of compressed air to perform work.

Pressure

Force applied per unit area.

Volumetric flow rate

The volume of fluid that passes through a given surface per unit time.

Friction torque

Torque that resists motion between two contacting surfaces.

Brakes

Devices that slow down or stop motion by applying friction.

Clutches

Devices that engage or disengage power flow in a mechanical system.

Spring

An elastic device that can absorb energy and return to its original shape.

Load path

The route through which forces are transmitted in a mechanical system.

Power path

The route through which energy flows in a mechanical system.

Torque capacity

The maximum torque that a component can transmit without failing.

Bearing load

The force that a bearing must support due to external loads.

Material fatigue

The weakening of a material caused by repeated loading and unloading.

Clamping friction

The friction that holds joint members together by the preload of a bolt.

Effective radius

The average radius over which friction acts in a brake or clutch.

Capstan equation

A formula used to relate the tension on the tight and slack sides of a belt.

Shear force

A force that acts parallel to the surface of a material.

Direct shear

The shear force acting directly along the plane of a joint.

Network analysis

The process of tracing paths to determine load and power distribution in a mechanical system.

Fluid resistance

The resistance faced by a fluid as it flows through a system.

Mechanical vibration

Oscillations of a mechanical component about an equilibrium position.

Overheating

Excessive heat generation that can cause failure due to thermal limits.

Misalignment

A positional discrepancy between connected components that can lead to wear and failure.

Energy dissipation

The process of converting mechanical energy into heat, sound, or other forms of energy.