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1.2.1Motion, Forces and Energy

Speed and Velocity

5 min read 6 parts Lesson 4 of 36 1 quiz

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Section 1 of 6Speed

Speed
Speed distance travelled per unit time, a scalar
Equation
  • Equation v = s ÷ t for constant speed
Units
  • Units v in metres per second (m/s), s in metres (m) and t in seconds (s)
Formula triangle
  • Formula triangle cover the quantity to find

Section 2 of 6Average speed

1Average speed
Average speed total distance travelled ÷ total time taken
2Variable journeys
  • Variable journeys a car speeds up, slows down and stops, so average speed is more useful than instantaneous speed
3Typical values
  • Typical values walking 1.5 m/s, running 3 m/s, cycling 6 m/s, a plane about 250 m/s

Section 3 of 6Velocity

Velocity
Velocity speed in a stated direction, a vector
Equation
  • Equation v = s ÷ t, where s is displacement
Direction
  • Direction it must be stated with the answer
Sign
  • Sign either direction can be positive if the opposite direction is negative and the choice is consistent

Section 4 of 6More from the specification

More from the specification
Speed vs Velocity in Kinematics
  • Speed is a scalar quantity measuring the rate of distance covered,
  • whereas velocity is a vector describing the rate of change of displacement in a specific direction.
Distance-Time Graph Analysis
  • On a distance-time graph, the gradient represents instantaneous speed;
    • an increasing gradient indicates positive acceleration,
  • while a flat line represents zero speed.
Speed-Time Graphs and Acceleration
  • On a speed-time graph, the gradient represents linear acceleration (a = Δv / Δt),
    What the symbols mean: a = acceleration (m s−2) · v = final velocity · u = initial velocity (m s−1) · Δv = change in velocity · t = time taken (s)
  • and the geometric area beneath the line represents the total distance travelled by the object.
Air Resistance and Terminal Fall Speed
  • When an object falls under gravity, upward air resistance increases with speed until it equals downward gravitational force,
  • resulting in zero net force and terminal velocity.
Resultant force
  • Another name for net force.
Gravitational field
  • Region where mass experiences gravitational force.
Field strength
  • G = Fg/m.
Acceleration
  • Rate of change of velocity.
Gradient
  • Slope of a graph line.
Resistance
  • Opposition to current, R = V / I, in ohms (Ω).
Weight
  • Gravitational force on a mass.
Terminal
  • Connection point of a cell, labelled + or −.
Accelerating
  • Speeding up.
Speed-time graph
  • Graph of speed against time.
Distance-time graph
  • Graph of distance against time showing movement.

Section 5 of 6Key terms

TermMeaning
SpeedDistance travelled per unit time.
Average speedTotal distance divided by total time.
VelocitySpeed in a given direction.
ScalarQuantity with magnitude only.
VectorQuantity with magnitude and direction.
DisplacementStraight-line distance in a direction.

Section 6 of 6Exam technique

1
Using the average of the starting and ending speed as the average speed — use total distance ÷ total time.
2
Giving velocity without direction — velocity needs a direction.
3
Mixing hours and seconds in the same equation — use consistent units.
4
Confusing distance and displacement — velocity uses displacement.
Physics 0625 & 9702 SUVAT Mastery Graph Interpretation

Constant Acceleration Equations (SUVAT) & Slopes

v = u + at  |  s = ut + ½at2  |  v2 = u2 + 2as  |  s = ½(u + v)t

  • Displacement-Time Graph: Gradient = Velocity (curve = accelerating).
  • Velocity-Time Graph: Gradient = Acceleration; Area under curve = Distance travelled / Displacement.
  • Free Fall in vacuum: a = g ≈ 9.81 m/s2 downwards (air resistance negligible).