Last-night recap — not a substitute for the lessons
| Quantity | Equation | SI units |
|---|---|---|
| Average speed | $v = d/t$ | m/s, m, s |
| Acceleration | $a = (v-u)/t$ | m/s$^2$, m/s, s |
| Final speed (no time) | $v^2 = u^2 + 2as$ | m/s, m/s$^2$, m |
| Unbalanced force | $F = m a$ | N, kg, m/s$^2$ |
| Weight | $W = m g$ | N, kg, N/kg |
| Stopping distance | thinking + braking | m |
| Thinking distance | speed $\times$ reaction time | m, m/s, s |
| Hooke’s law | $F = k e$ | N, N/m, m |
Units you must use (1.1): kg, m, m/s, m/s², N, s, N/kg.
Scalar: magnitude only (mass, speed, distance, time). Vector: magnitude and direction (force, velocity, acceleration, weight). Force is a vector.
Constant speed of a falling object when air resistance = weight, so resultant force is zero and acceleration is zero. Forces are still there.
Initial linear region of a force–extension graph: $F \propto e$, $F=ke$. Gradient is $k$. Do not use points after the graph curves.
The material recovers its original shape after the deforming force is removed. Permanent change is plastic deformation.
Distance–time
Gradient = speed. Horizontal = stationary. Steeper = faster. Curve getting steeper = accelerating.
Velocity–time
Gradient = acceleration. Horizontal (above axis) = constant velocity, still moving. Area under line = distance. Split into triangles and rectangles.