Edexcel iGCSE Physics -1.1 -1.2P SI Base and Derived Units- Study Notes- New Syllabus

Edexcel iGCSE Physics -1.1 -1.2P SI Base and Derived Units- Study Notes- New syllabus

Edexcel iGCSE Physics -1.1 -1.2P SI Base and Derived Units- Study Notes -Edexcel iGCSE Physics – per latest Syllabus.

Key Concepts:

1.1 use the following units: kilogram (kg), metre (m), metre/second (m/s), metre/second2 (m/s2 ), newton (N), second (s) and newton/kilogram (N/kg)
1.2P use the following units: newton metre (Nm), kilogram metre/second (kg m/s)

Edexcel iGCSE Physics -Concise Summary Notes- All Topics

SI Units Used in Mechanics

In physics, measurements must be made using standard units so that results are consistent and comparable. The internationally agreed system of units is called the SI system. In mechanics, a small number of SI units are used repeatedly to describe motion and forces.

Required SI Units

  • kilogram (kg)
  • metre (m)
  • second (s)
  • metre per second (m/s)
  • metre per second squared (m/s²)
  • newton (N)
  • newton per kilogram (N/kg)

Meaning of Each Unit

Kilogram (kg)

  • Unit of mass.
  • Mass is the amount of matter in an object.
  • Mass does not change with location.

Metre (m)

  • Unit of length or distance.

Second (s)

  • Unit of time.

Metre per second (m/s)

  • Unit of speed or velocity.
  • Measures how fast an object moves.
  • Formula: \( \mathrm{speed = \dfrac{distance}{time}} \)

Metre per second squared (m/s²)

  • Unit of acceleration.
  • Measures how quickly velocity changes.
  • Formula: \( \mathrm{acceleration = \dfrac{change\ in\ velocity}{time}} \)

Newton (N)

  • Unit of force.
  • 1 N is the force needed to accelerate a 1 kg mass at 1 m/s².
  • Formula: \( \mathrm{force = mass \times acceleration} \)

Newton per kilogram (N/kg)

  • Unit of gravitational field strength.
  • Represents the force acting on 1 kg of mass.
  • On Earth, \( \mathrm{g \approx 9.8\ N/kg} \).
  • Formula: \( \mathrm{weight = mass \times g} \)

Key Idea

  • Correct units must always be used in calculations.
  • Equations only work properly when SI units are used.
  • Forces, motion, and weight are all linked through these units.

Example

A cyclist travels a distance of \( \mathrm{120\ m} \) in \( \mathrm{8\ s} \). Calculate the speed of the cyclist.

▶️ Answer / Explanation

Use: \( \mathrm{speed = \dfrac{distance}{time}} \)

\( \mathrm{speed = \dfrac{120}{8}} \)

\( \mathrm{speed = 15\ m/s} \)

Example 

An object of mass \( \mathrm{4\ kg} \) is lifted on Earth. Calculate its weight. (Take \( \mathrm{g = 9.8\ N/kg} \))

▶️ Answer / Explanation

Use: \( \mathrm{weight = mass \times g} \)

\( \mathrm{weight = 4 \times 9.8} \)

\( \mathrm{weight = 39.2\ N} \)

Moments and Momentum Units

In mechanics, some physical quantities involve both force and distance or mass and velocity. These quantities use compound SI units such as newton metre (Nm) and kilogram metre per second (kg m/s).

Required Units

  • newton metre (Nm)
  • kilogram metre per second (kg m/s)

Newton Metre (Nm)

The unit newton metre (Nm) is used to measure the moment of a force.

  • A moment describes the turning effect of a force.
  • It depends on the size of the force and its distance from the pivot.
  • Formula: \( \mathrm{moment = force \times perpendicular\ distance} \)
  • Unit: newton × metre = newton metre (Nm)

Kilogram Metre per Second (kg m/s)

The unit kilogram metre per second (kg m/s) is used to measure momentum.

  • Momentum describes how difficult it is to stop a moving object.
  • It depends on both mass and velocity.
  • Formula: \( \mathrm{momentum = mass \times velocity} \)
  • Unit: kilogram × metre per second = kg m/s

Key Idea

  • Moments are used to analyse turning effects and balance.
  • Momentum is used to analyse collisions and motion.
  • Correct SI units must always be included in answers.

Example

A force of \( \mathrm{12\ N} \) acts perpendicular to a spanner at a distance of \( \mathrm{0.25\ m} \) from the pivot. Calculate the moment of the force.

▶️ Answer / Explanation

Use: \( \mathrm{moment = force \times distance} \)

\( \mathrm{moment = 12 \times 0.25} \)

\( \mathrm{moment = 3.0\ Nm} \)

Example 

A trolley of mass \( \mathrm{2.5\ kg} \) moves at a velocity of \( \mathrm{4\ m/s} \). Calculate the momentum of the trolley.

▶️ Answer / Explanation

Use: \( \mathrm{momentum = mass \times velocity} \)

\( \mathrm{momentum = 2.5 \times 4} \)

\( \mathrm{momentum = 10\ kg\,m/s} \)

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