Mayoor School, Ajmer
Physics / Revision Notes / Motion
Speed and Velocity
𝑠𝑝𝑒𝑒𝑑 =
𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒
𝑣=
𝑡𝑖𝑚𝑒
𝑑
unit: metres/second (m/s)
𝑡
Convert km/h to m/s by dividing by 3.6
Convert m/s to km/h by multiplying by 3.6
Average speed = total distance travelled / total time
Velocity is a VECTOR quantity (magnitude and direction) whereas Speed is a SCALAR quantity
(magnitude only)
Acceleration
Acceleration =rate of change of velocity
𝑎𝑐𝑐𝑒𝑙𝑒𝑟𝑎𝑡𝑖𝑜𝑛 =
𝑐ℎ𝑎𝑛𝑔𝑒 𝑜𝑓 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦
𝑡𝑖𝑚𝑒 𝑡𝑎𝑘𝑒𝑛 𝑡𝑜 𝑐ℎ𝑎𝑛𝑔𝑒
unit: metres per second squared
𝑎=
Where
speeding up/ slowing down /changing direction
m/s2
𝑣−𝑢
𝑡
v = final velocity;
can be rearranged as
𝑡=
𝑣−𝑢
𝑎
u = initial velocity ; t = time taken
or
𝑣 = 𝑢 + 𝑎𝑡
and a = acceleration
Travel Graphs
The velocity can be found from the gradient of the graph
Steady velocity ~ stationary ~ steady negative velocity
accelerating ~ steady velocity ~ decelerating
Speed vs Time and Distance vs Time Graphs
speed
a)
c)
b)
time
time
time
distance
speed
speed
d)
time
f)
e)
time
time
time
time
time
distance
speed
distance
g)
distance
distance
time
h)
time
i)
time
time
time
time
Which of the graphs above best shows the motion of:
1) An aeroplanetime
taking off?
time
__ and __
2) A car driving along a motorway?
__ and __
3) A rock falling off a cliff?
__ and __
4) A car approaching red traffic lights?
__ and __
5) A car which has stopped at a pedestrian crossing?
__ only
6) A car, initially travelling at 30mph, which
accelerates to overtake a lorry?
__ and __
time