# Motion

## Periodic Motion

Periodic Motion or Oscillatory Motion: When an object repeats its motion after every fixed interval of time, the motion of the object is called PERIODIC MOTION OR OSCILLATORY MOTION.

In many wall clocks pendulum is used even today. A device having a string suspended with a fixed point with a bob at bottom is called pendulum.

The motion of pendulum starting from one extreme end to another extreme end and back to the first extreme end is called one oscillation. Similarly, the motion of a simple pendulum from its mean position to extreme left and extreme right and back to the mean position is called one oscillation.

Time Period: Time taken to complete one oscillation by the pendulum is called time period.

Time Period = time/number of oscillations

#### Review Question:

Question 1: A pendulum takes 20 second to complete 10 oscillations, calculate its time period.

Answer: Given, Number of oscillations = 10

Time taken = 20 second

We know that, Time Period = Time ÷ number of oscillations

= 20 ÷ 10 = 2 second

### Speed and Time

Unit of Time: Time is measured in second. Thus, unit of time is second. Second is denoted by āsā.

60 second = 1 minute

60 minute = 1 hour

24 hour = 1 day

7 day = 1 week

365 days = 1 year

Unit of speed: Unit of speed is meter/second (m/s), or metre/minute (m/min) or kilometer/hour (km/h).

1000 metre (m) = 1 kilometer (km)

Speedometer: A device used to measure the speed of a vehicle is called SPEEDOMETER.

Odometer: A device used to measure the distance covered by a vehicle.

Distance Time Graph: When distance covered by an object and time taken to cover the distance is represented on a graph, the graph is called distance time graph.

If a vehicle cover a distance of 5 km every hour and travels for 5 hours, the time distance time graph for the given vehicle can be plotted as follows using the table given below:

 Time(in hour) 1 2 3 4 5 Distance(in km) 5 10 15 20 25

Distance time graph of a moving vehicle with a constant speed is a straight slanting line.

Speed-time graph for the same vehicle will be a straight line parallel to x-axis.

#### Important Points:

• Motion: When an object changes its position with elapse of time in respect to a stationary object, such as a building, electric pole, etc., the object is said to be in motion.
• Slow and Fast Motion: If an object A covers more distance and object B covers less distance in same time, then object A is called in Fast Motion and object B is called in Slow Motion.
• Rectilinear Motion: Motion along a straight line is known as RECTILINEAR MOTION OR MOTION ALONG A STRAIGHT LINE.
• Curvilinear Motion: Motion along a curve line is known as CURVILINEAR MOTION.
• Circular Motion: Motion along a circle is known as CIRCULAR MOTION.
• Speed: Distance covered by an object in unit time is called speed. This means Speed is equal to Distance upon Time.
• Uniform Speed: If an object covers a fixed distance in each unit of time the motion is known as UNIFORM MOTION or UNIFORM SPEED.
• Non-uniform Speed: If an object does not cover a fixed distance in each unit of time the motion is known as NON-UNIFORM MOTION or NON-UNIFORM SPEED.
• Average Speed: Total distance covered divided by total time taken is known as AVERAGE SPEED.
• Periodic Motion or Oscillatory Motion: When an object repeats its motion after every fixed interval of time, the motion of the object is called PERIODIC MOTION OR OSCILLATORY MOTION.
• Oscillation: The motion of pendulum starting from one extreme end to another extreme end and back to the first extreme end is called one oscillation.
• Time Period: Time taken to complete one oscillation by the pendulum is called time period.
• Unit of Time: Time is measured in second.
• Unit of speed: Unit of speed is meter/second (m/s).
• Speedometer: A device used to measure the speed of a vehicle is called SPEEDOMETER.
• Odometer: A device used to measure the distance covered by a vehicle.
• Distance time graph of a moving vehicle with a constant speed is a straight slanting line.
• Speed-time graph for the same vehicle will be a straight line parallel to x-axis.