Describing motion
● Speed
○ Distance traveled by an object in unit time
○ Speed = d/t
○ Measures m/s or km/hr or mph(miles per hour)
○ Gradient of distance-time graph
● Average speed
○ Total distance/ Total time
○ S.I = m/s
● Velocity
○ Velocity equals to displacement upon time
○ V= D/t
● Acceleration
○ The rate if change of an object’s velocity
○ Acceleration = change in velocity / time taken
○ A = v- u/t
○ Gradient of speed time graph
● Distance= Speed x time
● Displacement= Object’s overall change in position
● Conversion
○ km/hr → m/s (x 5/18)
○ m/s → km/hr (x 18/5)
● Properties of distance-time graph
○ A horizontal line means object is
stationary
○ A straight line means constant speed
○ If the gradient increases the object is
speeding up(accelerating)
○ If the gradient decreases the object is
slowing down (decelerating)
○ If the line is going down, the object is
moving backwards
○ The speed of an object is given by the
gradient of the line
● Motion
○ Uniform motion
■ Constant speed/ fixed rate
■ Object travels equal distance
○ Non-uniform motion
■ Unequal distance
■ Unequal time
● Velocity time graph
○ You can find the acceleration
○ It shows how the velocity(or speed) of an object
changes overtime
○ If the line is horizontal, it is constant (no
acceleration)
○ If the line slopes upwards then the object is
accelerating(speeding up)
○ If the line goes down then the object is
decelerating(slowing down)
○ Deceleration = Negative acceleration
● Calculating distance
○ The distance traveled can be found from the area beneath the graph
○ If the area beneath the graph forms triangle (the object is accelerating or decelerating) then the
area can be determined by ½ x base x height
○ If the area beneath the graph is a rectangle (constant velocity) then the area can be determined
using the formula → area = l x b
● The acceleration of an object is given by the gradient of the graph → Gradient = y2-y1/x2-x1
○ Lines that slope downwards have negative gradients and so can be said to have negative
acceleration or deceleration
○ If the gradient of the line changes then the acceleration of the body must be changing.
○ A line with constant gradient represents constant acceleration(linear motion)
○ A curved line represents changing accelerating either decreasing(if gradient gets smaller) or
increasing(if gradient gets bigger)
● Free fall
○ In the absence of air resistance,all objects will fall with the same acceleration regardless of their
mass
○ This acceleration is equal to the gravitational field strength and is approximately 10m/s2 near
the earth’s surface
○ So as long as the air resistance remains insignificant, the speed of a falling object will increase
at a steady rate, getting larger the longer it falls for
● Final acceleration = final gradient = rise/run
