Kinematics
Speed, distance & acceleration
Distance:
Speed:
the rate of change of distance
distance / time
The total length of a journey travelled
Acceleration:
the rate of change of speed
speed / time
*actually a vector – should be velocity
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'Instantaneous' measurement
Measured at a specific point in time
Only valid at that instant
'Average' measurement:
Calculated over the entire journey
eg. av. speed = total d / total t
Vector or Scalar
Scalar quantities describe magnitude
Vector quantities describe magnitude and direction
Displacement
Velocity
Distance
Speed
Graphs
Gradient – rate of change of:
Displacement-time graph – velocity
Velocity-time graph – acceleration
Area – total change in:
Acceleration-time graph – velocity
Velocity-time graph – displacement
Constant acceleration formulae (suvat equations)
If acceleration is constant, there are 5 key quantities that define an object's motion
s - displacement
u - initial velocity
v - final velocity
a - acceleration
t - time
Equations
a = (v-u)/t
s = ut + 1/2 • at^2
s = vt - 1/2 • at^2
v^2 = u^2 + 2as
s = (u+v)/2 • t
Solving problems
- Convert where needed into SI units
- Write down the 3 known suvat quantities, and the one we want to find
- Choose appropriate equation from the above
- Substitute into the equation