Let us discuss some important definitions related to motion.
• Reference point:
It is the point around which the location of an object is measured. It is also known as the origin.
• Scalar quantity:
This physical quantity has its own magnitude but not specific direction. Example- distance, speed etc.
• Vector quantity :
This physical quantity has both magnitudes as well as specific direction. Example – displacement, velocity, etc.
• Distance :
1. The actual path or length covered by a body during its journey from the initial position to the final position.
2. It’s a scalar quantity
3. Ex – Rohan travelled 37 km.
• Displacement :
1. The shortest possible distance covered by a body during it’s journey from the initial position to the final position.
2. It’s a vector quantity.
3. Example – Rohan travelled 37 km in South-West direction.
4. It can be zero if the initial position and final position are the same. Ex – circular motion.
• Motion can be one dimensional, two dimensional and three dimensional on the basis of direction.
One dimensional - It is also termed as motion in a straight line. When an object moves in a straight line with respect to the observer via using only one coordinate out of three.
Example: the motion of the lift, walking in Narrow Street etc.
Two dimensional – When an object moves via using two out of the three coordinates is termed as two dimensional. For example the motion of a car, the motion of rolling ball etc.
Three dimensional – When a body moves via using all the three coordinates and even movement in any direction is termed as three-dimensional motion. For example a flying kite, a moving aeroplane etc.
- Uniform motion:
When a body travels equal distance in equal interval of time .
- Non uniform motion:
When a body travels unequal distance in equal interval of time.
- Speed :
- Measurements of distance travelled per unit time .
- Speed – distance travelled / time taken.
- V – S / T
- I unit – meter / sec i.e., m/s
- Average speed :
Total distance travelled / total time taken.
- Velocity :
- It’s speed of the body in given direction.
- Velocity – displacement / time
- Its a vector quantity.
- Vavg ( for non uniform motion ) – total displacement / total time
- Vavg ( for uniform motion ) - initial distance (u) + final distance (v) / 2 or u + v / 2
- S I unit of velocity – ms -1
- It can be positive, negative or zero.
- Acceleration :
- It is seen in non uniform motion and it can be defined as the rate of change of velocity per unit time.
- Acceleration (a) = change in velocity (v – u) / t
- a = v – u / t
- If v > u then (a) will be positive.
- If u > v then (a) will be negative.
- Deaceleration : a = v – u / t
- Equation of motion for uniformly accelerated motion:
- First equation :
v – u + at
Final velocity = initial velocity + acceleration × time
- Second equation :
S = ut + ½ at2
- Third equation :
V2 = u2 + 2as