Oscillatory Motion

Lesson (1) Unit (1) Prep (2)Made by:

Dr. Niveen Fawzy

Motion & its types • Motion: It’s the change in an object’s

position as time passes.• Types of motion• 1- Translational motion• 2- Periodic motion• First Translational motion• Its the motion in which the object’s position is

changed relative to a fixed point (or a fixed frame of reference) from time to time between initial & final positions

Examples on translational motion

A person’s motion A bicycle’s motion

A car’s motion

Train’s motion

Second: Periodic motion• It’s a motion which is repeated regularly in

equal periods of time {moves periodically back & forth over the same path }

• N.B : It doesn’t have initial & final positions

• Examples of periodic motion

1-Oscillatory(vibrational) motion 2- Circular motion 3- Wave motion

Concept of Oscillatory Motion

Steps: -Push with your hand gently the pendulum & leave it &use stopwatch to record time taken by pendulum to repeat its movement several timesObservation:It will move on both sides around its original position (A) The displacement of oscillating body around its original position are equalThis motion is repeated in equal time interval-Maximum velocity is at point (A) & decreases gradually when it goes away from point (A), so maximum KE at point (A)ConclusionThe oscillatory body moves around its rest point & repeated at equal time intervals

Oscillatory motion

•Note that:The movement of earth’s crust during earthquakes is

considered an oscillatory motionWhile ,The motion of rotary bee is a periodic motion but not

considered an oscillatory motion because its not repeated on the 2 sides of its rest point

Application for oscillatory motion Microwave oven:Its function depend on the vibration of water molecules in food by effect of microwaves.This oscillatory motion causes the collision of water molecules & this increases its heatEnergy in very short time so food is cooked faster

Give reason• Food must be put in glass , pottery or ceramic

pots while metallic pots are not used• Because metallic pots reflect microwaves

Graphical representation of oscillatory motion Tools: -Spring -weight-holder-pencilSteps: 1- Fix pencil to weight , then tie one end to spring 2- let the pencil’s tip touch the mid point of paper tape 3-Roll the paper tape regularly , pull the weight downwards & leave itObservation:The pencil draws the shape of oscillatory motionConclusion:The simple harmonic motion is the simplest oscillatory motion

The concepts related to oscillatory motion • 1- Amplitude 2- Complete oscillation• 3- Periodic time 4- Frequency

• First: Amplitude• It’s the maximum displacement done by the

oscillating body away from its original position {How far away an oscillating body can get from center}

• Maximum displacement in a pendulum:• AB = BA = BC = CB• Each of them is an amplitude• Measuring unit (cm) or (m)• What is meant by: The amplitude of an oscillating body is

2cm• The maximum displacement away from its original position

is 2cm

Second: Complete oscillation

Third: Periodic time

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Fourth: Frequency:

Problems :

Problem :

Problems:

Model answers of book lesson(1) unit(1)

• Question (5):

• X is the motion of string • Y is the motion of spring• Z is the motion of pendulum