Physics Velocity Notes
2: SPEED, VELOCITY AND ACCELERATION
2.1 Distance and Displacement
• Distance is the total length covered by a moving object irrespective of the direction of motion, i.e. only the magnitude is of importance.
• Displacement is the distance measured in straight line AND in a specific d__________________. Both magnitude and d_________________ are important.
Example 1
A car travels 5 km due east and makes a U-turn back to travel a further distance of 3 km.
Find (a) the distance covered, (b) its displacement.
|(a) Distance covered = 5 + 3 = 8 km |[pic] |
|(b) Displacement = 5 – 3 = 2 km due east of starting point. | |
2.2 Speed and Velocity (Text pg 48: Unit 3.2)
Vectors and Scalars
• scalars – magnitude ONLY
• vectors – magnitude + direction
Speed
• defined as the rate of change of distance, in other words, distance moved per unit time
• instantaneous speed: speed at that particular instant Average speed = Total distance Total time
• SI unit : metre per second (ms-1)
• 1 ms-1 = km h-1
=
Example 2
In the 1988 Seoul Olympics, Ben Johnson broke the world record to run 100 metres in 9.83 seconds. What was his average speed?
Average speed = 100 / 9.83 = 10.2 ms–1
Velocity
• Defined as the rate of change of displacement. It is speed in a specific direction.
• When asked for the velocity of an object, have to state the speed and direction of the object.
• 2 cars may have the same speed but different velocity.
• Negative sign indicates opposite direction
Example 3
If the time taken for the car in example 1 to move from O to E is 0.2 hour, calculate
(a) the average speed and (b) the average velocity.
(a) Average speed = total distance covered / total time taken = 8 / 0.2 = 40 km h–1
(b)
2.1 Distance and Displacement
• Distance is the total length covered by a moving object irrespective of the direction of motion, i.e. only the magnitude is of importance.
• Displacement is the distance measured in straight line AND in a specific d__________________. Both magnitude and d_________________ are important.
Example 1
A car travels 5 km due east and makes a U-turn back to travel a further distance of 3 km.
Find (a) the distance covered, (b) its displacement.
|(a) Distance covered = 5 + 3 = 8 km |[pic] |
|(b) Displacement = 5 – 3 = 2 km due east of starting point. | |
2.2 Speed and Velocity (Text pg 48: Unit 3.2)
Vectors and Scalars
• scalars – magnitude ONLY
• vectors – magnitude + direction
Speed
• defined as the rate of change of distance, in other words, distance moved per unit time
• instantaneous speed: speed at that particular instant Average speed = Total distance Total time
• SI unit : metre per second (ms-1)
• 1 ms-1 = km h-1
=
Example 2
In the 1988 Seoul Olympics, Ben Johnson broke the world record to run 100 metres in 9.83 seconds. What was his average speed?
Average speed = 100 / 9.83 = 10.2 ms–1
Velocity
• Defined as the rate of change of displacement. It is speed in a specific direction.
• When asked for the velocity of an object, have to state the speed and direction of the object.
• 2 cars may have the same speed but different velocity.
• Negative sign indicates opposite direction
Example 3
If the time taken for the car in example 1 to move from O to E is 0.2 hour, calculate
(a) the average speed and (b) the average velocity.
(a) Average speed = total distance covered / total time taken = 8 / 0.2 = 40 km h–1
(b)