1.2.2Forces and Their Effects
Speed and Velocity — Oxford AQA International GCSE Combined Science - Physics Revision Notes & Topical Questions
5 min read 6 parts Lesson 8 of 16
Part 1 of 5Speed
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
Part 2 of 5Average 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
Part 3 of 5Velocity
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
Part 4 of 5Equations summary
| Quantity | Equation | Unit |
|---|---|---|
| Speed | v = s ÷ t | m/s |
| Distance | s = v × t | m |
| Time | t = s ÷ v | s |
| Average speed | total distance ÷ total time | m/s |
Part 5 of 5More 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.
Key terms
| Term | Meaning |
|---|---|
| Speed | Distance travelled per unit time. |
| Average speed | Total distance divided by total time. |
| Velocity | Speed in a given direction. |
| Scalar | Quantity with magnitude only. |
| Vector | Quantity with magnitude and direction. |
| Displacement | Straight-line distance in a direction. |
Avoid these mistakes
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.
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