# Motion and Time

We know that motion is a phenomenon which changes it’s position over time and that it is of 4 types:- Rectilinear Motion, Circular Motion, Rotational Motion and Periodic Motion.

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## How to decide which object is moving fast or slow?

- The distance moved by objects in a given interval of time tells us which one is faster or slower.
- Let’s say for example you and your friend are doing a race and your friend is pedalling faster then you , so by this you can easily tell who is slow or fast.
- One who takes shortest time to cover a particular distance has the highest speed.

### What is Speed?

- Speed is how fast an object travels from one point to the other in a given interval of time.
- It is a scalar quantity.
- We calculate an object speed by a particular formula and that is; Speed= Distance/ Time
- For example; If we say that a train is travelling with a speed of 120km/hr that means the train covers a distance of 120 km in 1 hour.

### There are 2 types of Speed;

- Uniform Speed: If an object is moving on a straight line with constant speed then it is called as Uniform speed . Example: A car going on a straight road at a steady speed.
- Non-Uniform Speed : If an object on a straight line with variable speed then it is called as Non-uniform speed. Example: A person who is jogging on a road or in a park as he keeps changing his speed after a certain time.

## What do you mean by Oscillatory Motion:

- The to and fro motion of a simple pendulum is termed as an Oscillatory Motion.
- The pendulum has said to complete one motion when it goes from one extreme position to the other extreme position.
- The time taken by the pendulum to complete one oscillation is it’s Time Period.

### Unit of Time and Speed:

- The SI unit of time is second.
- The SI unit of speed is metre per second which is written as m/s.
- It came through the formula of distance/speed which gives us m/s.

Just for general Knowledge you can remember that one day has 86400 seconds and there are 8760 hours in a year.

- An instrument used for measuring the distance travelled by a vehicle is called an Odometer.

## Distance-Time Graph:

- The distance travelled by an object in a given period of time is shown in distance- time graph.
- Generally, the time is marked on the x-axis of the graph and the distance is marked in the y-axis of the graph.
- We can compare the speeds of different objects given in the graph by just looking at the angle of the lines.
- The steeper the line in the graph the fastest is the movement.

**The advantages of distance-time graph are:**

- It tells us about the position of the object at any time.
- It tells us about the velocity ( The rate of change of the position of an object is called velocity. It is a vector quantity) of the object at any time.

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