Dynamics Exam Review Flashcards

4. DYNAMICS

Definition: The force with which gravity acts on the mass of an object.
Key Points:
- The weight of an object increases with mass under the earth's gravitational force.
- Gravity varies with the distance from the center of the earth;
- As the distance increases, the weight decreases.
- Earth Gravity: 1 G = 32 ft/s² or 9.81 m/s².
- Formula: Weight = Mass × Gravity.

Definition: The amount of matter in an object which remains constant regardless of the object's location.
Unit of Measurement:
- English system: pounds.
- Metric system: kilograms.
- Slug (unit of mass in the English system).

Definition: Anything that causes motion, changes motion, stops motion, or prevents motion.
Work: The product of force applied to an object times the distance moved by the object.
Unit: Newtons (N).
- 1 Newton is defined as the force required to give a 1 kg mass an acceleration of 1 m/s².
- Thus, 1 N = 1 kg × m/s².

Definition: The propensity of objects to maintain their current state of motion (either rest or steady motion).
Key Points:
- Inertia is proportional to mass; greater mass = greater inertia.
- Example: During aircraft take-off, passengers feel pushed back into their seats due to inertia.

Formula: Work = Force (F) × Distance (D).
Key Point: If a force is applied and the object does not move, that results in no work done.
Unit of Work: Joule (J) in the Metric system.
- 1 Joule is defined as the work done by applying a force of 1 Newton through a distance of 1 meter.

Definition: The time rate of doing work.
Formula: Power = Work / Time.
Units:
- English system: ft·lb/sec.
- Metric system: J/sec (watt).
- Energy measurement: Horsepower.
- 1 Watt = 1 Joule/sec.
- 1 Horsepower = 746 Watts, 1 Horsepower = 550 ft·lbs/sec.

Example 1: Calculate the time for a 1750 W motor to lift a 285 kg piano to a window 16 m high.
Example 2: Power required to lift a 12500 lbs airplane to 3 feet in 1 minute; provide answer in horsepower.
Example 3: Horsepower to raise a 12000 lbs aircraft 6 feet in half a minute.

Definition: The capacity of an object to perform work, which cannot be created nor destroyed but only transferred.
- Types:
  - Potential Energy: stored energy due to position, configuration, or chemical composition.
  - Examples:
    1. Chemical energy in an aircraft battery ready for mechanical work when the starter switch is pressed.
    2. Mechanical energy stored in a compressed spring.
    3. Water behind a dam to produce mechanical energy when released.
  - Kinetic Energy: energy possessed by an object due to its motion.
  - Formula: KE = ½ × mass × velocity².

Definition: Energy in transit between two bodies due to temperature difference.
Key Points:
- Heat energy flows from hot to cool regions until equilibrium is reached.
- Methods of heat transfer include:
- Conduction
- Convection
- Radiation.

Definition: Change in momentum due to a specific force.
- Impulse = Force × Time.
Key Points:
- Forces applied briefly (impulsive forces) result in significant changes in momentum.

Principle: In a closed system with no external forces, the total momentum remains constant.
Illustration: When two masses act upon each other, their total momentum before interaction equals their total momentum after interaction.

Definition: Devices with a rotating rotor, free to move in one or more planes perpendicular to the rotation.
Characteristics:
1. A gyroscope maintains orientation due to angular momentum.
2. Useful for measuring or maintaining orientation in various instruments (aircraft).
3. Various physical entities can display gyroscopic properties.
- Gyroscope components include:
1. Rotor
2. Inner Gimbal
3. Outer Gimbal

Gyroscopic Rigidity: Gyroscopes maintain their axis of rotation, marked by:
- Mass of rotor,
- Angular speed,
- Radius of gyration or moment of inertia of the rotor.
Precession: The movement of the spin axis caused by applied forces; relevant in aviation, as it can indicate turning rate.

Friction: A force that opposes sliding movements between two surfaces.
Key Points:
- Can be advantageous (e.g., brakes, walking).
- Depends on surfaces in contact and acts in opposing directions to movement.

Static Friction: Acts between stationary objects, must be overcome to start motion
- Coefficient formula: μ = F/N (limiting friction).
Dynamic Friction: Occurs between moving objects; typically lower than static friction for the same materials.
Other Types:
- Dry Friction: Between solid surfaces.
- Fluid Friction: Between layers of a viscous fluid.
- Lubricated Friction: Fluid separates two solid surfaces.
- Skin Friction: Component of drag between solid bodies and fluid.
- Internal Friction: Resisting motion between elements in solids during deformation.