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Cause and Effect — what makes motion ‘accelerated’
Cause
The velocity of an object changes — in magnitude, in direction, or both
↓
Rate of change
change in velocity ÷ time interval
↓
Effect: the object has acceleration (even at constant speed, if direction changes)
Describing Motion Around Us
position, distance, displacement, speed, velocity, acceleration — and their graphs
4.1
Motion in a Straight Line
reference point · position · distance travelled · displacement · average speed · average velocity · average acceleration
4.2
Graphical Representation of Motion
plotting · position-time graph · velocity-time graph · slope · area under graph
4.3
Kinematic Equations for Motion in a Straight Line with Constant Acceleration
v = u + at · s = ut + ½at² · v² = u² + 2as
4.4
Motion in a Plane
two dimensions · circular motion · uniform circular motion · changing direction of velocity
- Position
- The distance and direction of an object from a reference point at an instant describes its position; if this changes with time, the object is in motion.
- Displacement
- The net change in the position of an object between two given instants of time.
- Average speed
- The total distance travelled divided by the time interval during which it is covered.
- Average velocity
- The change in position (displacement) divided by the time interval in which it occurs.
- Average acceleration
- The change in velocity of an object over a time interval divided by that time interval.
- Kinematic equations (constant a)
- v = u + at; s = ut + ½at²; v² = u² + 2as — relating s, t, u, v and a.
- Uniform circular motion
- Motion in a circular path at constant (uniform) speed; the direction of velocity keeps changing, so the motion is accelerated.
- Reference point
- A fixed point (an origin) chosen to describe where an object is; all positions are measured from it.
- At rest
- An object whose position does not change with time with respect to the chosen reference point.
- In motion
- An object whose position changes with time with respect to the chosen reference point.
- Instant of time
- A single reading of the clock — one point on the time axis.
- Time interval
- The gap between two instants of time; every average quantity is defined over a time interval.
- Total distance travelled
- The whole length of the path actually covered by the object, irrespective of direction.
- Magnitude
- The size of a quantity, without its direction.
- Slope of a graph
- The steepness of a line on a graph. Slope of a position-time graph gives velocity; slope of a velocity-time graph gives acceleration.
