Understanding Motion:
Motion means change in position of an object with respect to time.
Important idea:
- If position changes → object is in motion
- If position does not change → object is at rest
To describe this change properly, we need four key variables:
Time, Displacement, Velocity, Acceleration
Time, Displacement, Velocity, Acceleration
Time:
Time is the independent variable in motion.
Why is it important?
- All changes in motion happen over time
- Without time, we cannot measure speed or change
Key idea:
Motion is always studied as position vs time
Example:
If two cars travel the same distance but in different times, their motion is different.
Displacement - Position Change
Displacement tells us where the object is relative to its starting point
Important Properties:
- It is a vector quantity (has direction)
- It can be:
- positive
- negative
- zero
Special Case:
\(Displacement\) \(=\) \(0\) does NOT mean no motion
Example:
A runner completes one lap → \(displacement\) \(=\) \(0\) but \(distance\) \(≠\) \(0\)
A runner completes one lap → \(displacement\) \(=\) \(0\) but \(distance\) \(≠\) \(0\)
Velocity – Rate of Motion
Velocity tells us how fast position is changing and in which direction
Key Understanding:
- Velocity depends on:
- displacement
- time
- It is also a vector quantity
Important Concept:
Change in direction is equal to change in velocity.
Example:
A car moving in a circular path:
A car moving in a circular path:
- Speed is constant
- Velocity is changing
Acceleration – Change in Motion
Acceleration tells us how velocity changes with time
Types of Acceleration:
- Positive acceleration → speed increases
- Negative acceleration (retardation) → speed decreases
- Uniform acceleration → equal change in velocity in equal time
- Non-uniform acceleration → unequal change
Acceleration can occur due to:
- Change in speed
- Change in direction
- Change in both
Example:
- Straight road → acceleration only if speed changes
- Circular motion → acceleration even if speed is constant
Relationship Between Variables
(i) Displacement & Time → Velocity
- More displacement in less time → higher velocity
(ii) Velocity & Time → Acceleration
- If velocity changes with time → acceleration exists
(iii) Acceleration affects Velocity
- Positive acceleration → velocity increases
- Negative acceleration → velocity decreases
(iv) All variables are connected
Motion cannot be explained by one variable alone. They always work together