How to Revise Forces and Motion for IGCSE Physics

Forces and motion is the largest section in IGCSE Physics 0625. It carries significant marks across all papers.

What the syllabus covers

• Measurement of length, time, and mass
• Speed, velocity, and acceleration
• Distance-time and velocity-time graphs
• Forces and their effects
• Newton’s laws of motion
• Momentum and impulse (Extended)
• Turning effects of forces (moments)
• Centre of gravity and stability
• Density and pressure
• Energy stores and transfers
• Work, power, and efficiency

Step 1: graphs

Velocity-time and distance-time graphs appear frequently. Make sure you can:

• Plot both types from given data.
• Read speed, distance, or acceleration from a graph.
• Calculate gradient (= speed or acceleration).
• Calculate the area under a velocity-time graph (= distance).

Practice with 5 past paper graph questions.

Step 2: Newton’s laws

State each law precisely:

1. An object stays at rest or moves at constant velocity unless acted on by a resultant force.
2. Resultant force = mass x acceleration (F = ma).
3. For every action, there is an equal and opposite reaction.

For Newton’s second law, practice F = ma calculations with unit conversions (g to kg, km/h to m/s).

Step 3: momentum (Extended)

• momentum = mass x velocity
• Conservation of momentum: total momentum before = total momentum after (in a closed system)
• impulse = force x time = change in momentum

Work through collision and explosion problems. Remember that momentum is a vector: direction matters.

Step 4: moments

• moment = force x perpendicular distance from pivot
• Principle of moments: sum of clockwise moments = sum of anticlockwise moments

Practice beam-balance calculations. Remember to include the weight of the beam if it is not pivoted at its centre.

Step 5: energy

• KE = 0.5mv squared
• GPE = mgh
• Work done = Fd
• Power = work done / time
• Efficiency = useful output / total input

A frequent exam error is forgetting to square the velocity in the kinetic energy equation.

Step 6: pressure

• Pressure = force / area (solid surfaces)
• Pressure in a fluid = density x g x h

Know how to apply both equations and convert units (cm squared to m squared, g/cm cubed to kg/m cubed).