Kinetics Physics Notes PDF

TOPIC 2.2: KINETICS Displacement and Distance The aircraft may travel a **total distance of 2 km** as it veers left and right, but its displacement, measured only as the difference **between the start point and finish point, will be less.** **Displacement** refers to the position of an object rel...

TOPIC 2.2: KINETICS Displacement and Distance The aircraft may travel a **total distance of 2 km** as it veers left and right, but its displacement, measured only as the difference **between the start point and finish point, will be less.** **Displacement** refers to the position of an object relative to its point of origin. This is different to **distance** which is the total length travelled by an object from its point of origin. Speed and Velocity A similar distinction can be made between speed and velocity. They both refer to the distance travelled per unit of time, for example, miles per hour, Fig 2.2.2 metres per second etc. Speed is defined as the rate of change in distance with respect to time. Velocity is defined as the rate of change in displacement with respect to time. Average speed is distance travelled divided by time taken. Average velocity is the final displacement divided by the total time. Acceleration When an object has an initial velocity then, after a period of time, that velocity has changed (increased or decreased), the object is said to have **accelerated**. Acceleration can be positive or negative. Negative acceleration is called **deceleration**. Acceleration is the **rate of change in velocity**. Average acceleration is found by dividing the change in velocity by the total time taken for this change to occur. You will remember that force is defined as that which uses energy to produce a change in motion state. **NEWTON** explored this and formulated his three famous Laws. 1. A body will remain at rest or continue its uniform motion in a straight line until 2. The acceleration of a body is directly proportional to the force applied to it and 3. For every action, there is an equal and opposite reaction. The upward thrust of a rocket is the reaction to the force propelling the mass of hot gas downward Linear Motion Motion is said to be uniform if equal displacements occur in equal periods of time. In other words constant velocity. Average velocity = displacement/time Average speed = distance/time CIRCULAR MOTION In accordance with Newton's First Law, the object would shoot off on a straight path unless a Centripetal Force is continually applied to keep it turning along the curve. PERIODIC MOTION Periodic motion or simple harmonic motion refers to repeated motion, i.e. that which repeats over time. For example, the mass on a spring (below) or a pendulum. The energy contained in a body moving with SHM is called wave energy. A linear restoring force is one that gets proportionally larger with displacement from the equilibrium position. Elasticity is the property of an object or material which causes it to be restored to its original shape after distortion. It is said to be more elastic if it restores itself more precisely to its original configuration -- a piano wire is MORE elastic than a rubber band. The time that it takes to make one complete repetition or cycle is called the period of the motion. We will usually measure the period in seconds. Frequency is the number of cycles per second that an oscillator goes through. Frequency is measured in \"hertz\" which means cycles per second. **Vibration** is a term normally reserved for high frequency periodic motion Vibration experienced in an aircraft may originate from the **engines, turbulence, or from flight control flutter** due to worn hinges or linkage bearings. Metal fatigue can occur from such vibration. RESONANCE The natural or resonant frequency of an object is the frequency where that object vibrates naturally, or without an external force. If two objects have the same natural frequency and are joined to each other, when one of them vibrates, it can **transfer its wave energy to the other object** making it vibrate. This transfer of energy is known as **resonance.** Because resonance can induce vibration it can exert destructive forces on an aircraft. For example, it is possible to have portions of an aircraft, such as the **propeller**, vibrate in resonance at certain engine speeds. HARMONICS Harmonics exist as multiples of an original, natural frequency. That is, if the natural frequency is 100 Hz: - the 1st harmonic is at 200 Hz - and the 2nd harmonic is at 300 Hz et Harmonics can resonate as well as natural frequencies