equations of motion
this section introduces the basic physical quantities used to describe motion.
distance
distance is the total length of the actual path travelled by an object from start to finish.
- scalar quantity (no direction)
- always positive
- unit:
m
displacement
displacement is the straight-line distance in a specified direction from the starting point to the finishing point.
- vector quantity (magnitude and direction)
- can be positive, negative, or zero
- equal to the area under a velocity–time graph
- unit:
m
average speed
average speed is the total distance travelled divided by the time taken.
average speed = total distance / total time
- scalar quantity
- unit:
m s⁻¹
average velocity
average velocity is the total displacement divided by the time taken.
average velocity = total displacement / total time
- vector quantity
- unit:
m s⁻¹
instantaneous velocity
instantaneous velocity is the velocity of an object at a specific moment in time.
- equal to the gradient of the tangent to a displacement–time graph
acceleration
acceleration is the rate of change of velocity.
a = (v − u) / t
- vector quantity
- unit:
m s⁻² - equal to the gradient of a velocity–time graph
acceleration due to gravity (g)
g is the constant acceleration of an object in free fall near the earth’s surface.
- value:
9.81 m s⁻² - acts towards the centre of the earth