Quick Revision Notes: Motion and Time

Class: 7 Science (MP Board)

---

### Concept 1: Motion (गति)

• Motion: An object is said to be in motion if it changes its position with respect to time.
• Types of Motion (गति के प्रकार):
  1. Rectilinear Motion (सरल रेखीय गति): Motion along a straight line (e.g., marching soldiers, a car moving on a straight road).
  2. Circular Motion (वृत्तीय गति): Motion along a circular path (e.g., motion of the earth around the sun, hands of a clock).
  3. Periodic Motion (आवर्ती गति): Motion that repeats itself after regular intervals of time (e.g., a simple pendulum, swinging of a child).

---

### Concept 2: Slow or Fast Motion (धीमी या तेज गति)

• The distance covered by two different objects in the same time interval helps us decide which one is faster and which one is slower.
• Speed (चाल): The distance covered by an object in a unit time (per second or per hour) is called the speed of the object.

---

### Key Formulas (महत्वपूर्ण सूत्र)

1. Speed (चाल)

$$\text{Speed} = \frac{\text{Total Distance Covered}}{\text{Total Time Taken}}$$ In symbol form: $$v = \frac{d}{t}$$ Where:

• $v$ = Speed
• $d$ = Distance
• $t$ = Time

2. Distance (दूरी)

$$\text{Distance} = \text{Speed} \times \text{Time}$$ $$d = v \times t$$

3. Time (समय)

$$\text{Time} = \frac{\text{Distance}}{\text{Speed}}$$ $$t = \frac{d}{v}$$

---

### Concept 3: Units of Measurement (मापन के मात्रक)

• SI Unit of Distance (दूरी का एस.आई. मात्रक): Meter ($m$)
• SI Unit of Time (समय का एस.आई. मात्रक): Second ($s$)
• SI Unit of Speed (चाल का एस.आई. मात्रक): Meter per second ($m/s$)
• Other common units of speed: Kilometer per hour ($km/h$)

Conversion (परिवर्तन):

• To convert $km/h$ to $m/s$, multiply by $\frac{5}{18}$.
• To convert $m/s$ to $km/h$, multiply by $\frac{18}{5}$.

---

### Concept 4: Measurement of Time (समय का मापन)

• Ancient humans used periodic events in nature to measure time (e.g., day to night, one sunrise to the next, phases of the moon).
• Simple Pendulum (सरल लोलक):
  • Consists of a small metallic ball (bob) suspended from a rigid stand by a thread.
  • Oscillation (दोलन): One complete to-and-fro motion of the pendulum.
  • Time Period (आवर्त काल): The time taken by the pendulum to complete one oscillation.

---

### Concept 5: Distance-Time Graph (दूरी-समय ग्राफ)

• A graph that shows the relation between distance covered by an object and the time taken.
• Uniform Motion (एक समान गति): When an object moves along a straight line with a constant speed, its distance-time graph is a straight line.
• Non-Uniform Motion (असमान गति): If the speed of an object moving along a straight line keeps changing, its distance-time graph is not a straight line (it can be curved).