Singapore-Cambridge N(A)-Level Combined Science, Physics: Measurement, Forces and Energy, from SI units and measuring instruments through speed, acceleration and Newton's laws to work, energy and power

What this module is about

The Measurement, Forces and Energy module is the bedrock of N(A)-Level Combined Science Physics (SEAB 5105 and 5106). It teaches the language of physics, units and measurement, then uses it to describe how things move, why they move, and the energy behind the motion. The thread that runs through it is quantity: every idea here is something you can measure, calculate and check with the right unit.

This overview pulls the threads together and links to every dot point page in the module, each with its own worked answers and practice questions.

Physical quantities and measurement

The module opens with physical quantities and measurement. You need the SI base quantities and their units, for example length in metres, mass in kilograms and time in seconds. You also need to choose the right instrument for the job, a ruler or measuring cylinder, a balance, a stopwatch, and read it to a sensible precision. Getting units and precision right is rewarded throughout the rest of the module.

Describing motion

Next comes speed, acceleration and graphs. Speed is distance divided by time, and acceleration is the change in speed divided by the time taken. Motion is best read from graphs: on a distance-time graph the gradient gives the speed, while on a speed-time graph the gradient gives the acceleration and the area under the line gives the distance travelled.

Forces and Newton's laws

The third dot point is forces and Newton's laws. A force can change an object's shape, speed or direction. Mass (in kilograms) is the amount of matter and is the same everywhere; weight (in newtons) is the force of gravity on that mass and depends on gravitational field strength. The key relationship is that the resultant force equals mass times acceleration, which links the cause of motion to the change it produces.

Work, energy and power

The module finishes with work, energy and power. Energy is stored in various ways, for example as kinetic energy in moving objects and gravitational potential energy in raised objects, and the principle of conservation of energy says it is never created or destroyed, only transferred. Work done equals force times distance, kinetic energy equals one half times mass times speed squared, and power equals work done divided by time.

How this module is examined

• Choose instruments and units sensibly. Match the instrument to the quantity and quote every answer with its correct unit.
• Read graphs for the right thing. Gradient on a distance-time graph is speed; on a speed-time graph it is acceleration, and area is distance.
• Apply the formulae cleanly. Show $F = ma$, work = force x distance, kinetic energy = half x mass x speed squared, and power = work / time, with substitution and units.

Check your knowledge

A mix of recall and application questions covering the module. Attempt them under timed conditions, then check against the solutions, and use the dot point pages for fuller practice.

1. State the SI units of length, mass and time. (2 marks)
2. Explain the difference between mass and weight. (2 marks)
3. A car travels 100 m in 5 s at a steady speed. Calculate its speed. (2 marks)
4. State what the area under a speed-time graph represents. (1 mark)
5. A resultant force of 12 N acts on a 3 kg mass. Calculate the acceleration. (2 marks)
6. Calculate the kinetic energy of a 4 kg object moving at 5 m/s. (2 marks)