Doc Brown's GCSE OCR 21st Century Science-Physics Revision Notes

OCR GCSE 21st Century Science Physics Module P4 Explaining motion

P4.1 How can we describe motion?

• 1. be apply the following equation to situations where an average speed is involved:

• speed (m/s) = distance travelled (m) / time taken (s)

• s = d/t

• 2. Be able to distinguish between average speed and instantaneous speed (in effect, an average over a short time interval) for examples of motion where speed is changing

• 3. HT only: understand that the displacement of an object at a given moment is its net distance from its starting point together with an indication of direction

• 4. Be able to draw and interpret a distance-time (or displacement-time) graph for an object that is:

• a) stationary

• b) moving at constant speed

• c) HT only: moving with increasing or decreasing speed

• 5. Be able to interpret a steeper gradient of a distance-time graph as a higher speed

• 6. HT only: Be able to calculate a speed from the gradient of a straight section of a distance-time graph

• 7. Be able to draw and interpret a speed-time graph for an object that is:

• a) stationary

• b) moving in a straight line with constant speed

• c) moving in a straight line with steadily increasing or decreasing speed (but no change of direction)

• 8. understand that in many everyday situations, acceleration is used to mean the change in speed of an object in a given time interval

• 9. know that the instantaneous velocity of an object is its instantaneous speed together with an indication of the direction

• 10. HT only: understand that the velocity of an object moving in a straight line is positive if it is moving in one direction and negative if it is moving in the opposite direction

• 11. HT only: Be able to draw and interpret a velocity-time graph for an object that is:

• a) stationary

• b) moving in a straight line with constant speed

• c) moving in a straight line with steadily increasing or decreasing speed (including situations involving a change of direction).

• 12. HT only: Be able to calculate the acceleration from the gradient of a velocity–time graph (or from a speed- time graph in situations where direction of motion is constant)

• 13. Be able to calculate acceleration using the equation:

• acceleration (m/s2) = change in velocity (m/s) / time taken (s)

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