Forces and Motion
Speed, Velocity and Acceleration
Pearson Edexcel International GCSE Physics
Speed
average speed = distance moved / time takenv = s / t
- Rearranged: s = v × t, t = s / v.
- Average speed: average speed = distance travelled / time taken, using the total distance and the total time for the whole journey.
- Velocity is speed in a given direction.
| Quantity | Symbol | Unit |
|---|---|---|
| distance moved | s | m |
| time taken | t | s |
| average speed | v | m/s |
| initial velocity | u | m/s |
| final velocity | v | m/s |
| acceleration | a | m/s2 |
Acceleration
acceleration = change in velocity / time takena = (v − u) / t
- Acceleration = change in velocity / time taken.
- Rearranged: v = u + a × t, t = (v − u) / a.
- A slowing object has a negative acceleration: a deceleration.
Distance-time graphs
| Shape | Motion |
|---|---|
| horizontal line | at rest |
| straight line sloping up | constant speed |
| curve getting steeper | speed is increasing |
| curve getting less steep | speed is decreasing |
- The gradient of graph is equal to the speed.
- A steeper line: the gradient is larger, so the speed is greater.
- Constant acceleration from rest: the line starts at origin and has positive gradient throughout, and the gradient of line increases over time.
Velocity-time graphs
| Shape | Motion |
|---|---|
| horizontal line | velocity is constant |
| straight line sloping up | constant acceleration |
| straight line sloping down | constant deceleration |
| line on the time axis | at rest |
- Acceleration is the gradient of the graph. A straight line: the graph has a constant gradient, so the acceleration is constant.
- Constant acceleration from rest: a straight line that starts at origin, with a positive gradient.
- A smaller deceleration: a line that is less steep.
- On a curve: the acceleration at a time is the gradient of the tangent at that time.
Distance from the area
- Distance travelled = area under graph.
- Straight-line sections: split the area into rectangles and triangles and add them. Under a curve: count the squares.
- Never find the distance as change in speed × time.
The equation v2 = u2 + 2as
(final speed)2 = (initial speed)2 + (2 × acceleration × distance moved)v2 = u2 + (2 × a × s)
- Rearranged: s = (v2 − u2) / 2a, a = (v2 − u2) / 2s.
- Coming to rest: the final speed v is 0 and the acceleration is negative. Give the distance as a positive value.
Investigating motion
Method: speed of an object down a ramp
- Mark two points a measured distance apart on the ramp with a tape measure.
- Release the object from the same start point each time.
- Measure the time taken to travel between the markers with a stopwatch.
- Calculate the average speed: speed = distance / time.
- Repeat and calculate a mean.
- Change the surface material, the independent variable, and measure the average speed, the dependent variable. Keep the height of ramp, the mass of block and the distance travelled down the ramp constant.
Two light gates connected to a data logger: the speed at each gate and the distance between the gates give the acceleration from v2 = u2 + 2as.
These notes are part of an Excel with Osman subscription and are not available to print.
That was one page of 32
The rest of Edexcel International GCSE Physics is written the same way
The other 31 pages of Edexcel International GCSE Physics are written exactly like this one, with the mark scheme wording highlighted throughout. A year of the whole course is $6.99.
Subscriptions open as soon as payment processing is approved.