1. Gravitational Forces What is gravity? Gravity is a force of attraction between objects that have mass. The bigger the mass → the stronger the gravity. The closer the objects → the stronger the gravity. Mass vs Weight Mass Amount of matter in an object Measured in kilograms (kg) Stays the same everywhere Measured with a balance Weight Force of gravity acting on an object Measured in newtons (N) Changes depending on gravity Measured with a spring scale Example Your mass = 50 kg (same on Earth and Moon) Your weight = different (because gravity changes) Formula for Weight F = mg F = weight (N) m = mass (kg) g = gravitational field strength Earth: 9.8 N/kg (≈ 10 N/kg) Example A boy has a mass of 40 kg. What is his weight? F = mg F = 40 × 10 F = 400 N 2. Unit Conversions 1 kg = 1000 g 1 g = 0.001 kg 1 Mg = 1 000 000 g 1 g = 0.000001 Mg Tips kg → g = ×1000 g → kg = ÷1000 g → Mg = ÷1 000 000 Mg → g = ×1 000 000 3. Magnetism Magnetic vs Non-Magnetic Materials Magnetic: iron, steel, nickel, cobalt Non-magnetic: plastic, wood, glass Uses of Magnets Fridges Compasses Electric motors Speakers Magnetic Poles North pole (N) South pole (S) Rule Like poles repel (N–N, S–S) Unlike poles attract (N–S) Magnetic Fields Area around a magnet where force is felt Represented by field lines Field Line Rules Go from North → South Never cross Closer lines = stronger field 4. Electrostatics What is electrostatics? Study of charges at rest Types of Charges Positive (+) Negative (−) Rule Like charges repel Unlike charges attract Charging by Friction When two objects are rubbed together Electrons move from one object to another One becomes negative, the other positive Example Rub a balloon on your hair → it sticks to the wall Interaction of Charges Positive + Positive → repel Negative + Negative → repel Positive + Negative → attract 5. Polarisation (NEW) What is polarisation? Polarisation happens when charges in a neutral object rearrange due to a nearby charged object

1. Gravitational ForcesWhat is gravity?

  • Gravity is a force of attraction between objects that have mass.

  • The bigger the mass → the stronger the gravity.

  • The closer the objects → the stronger the gravity.

Mass vs WeightMass

  • Amount of matter in an object

  • Measured in kilograms (kg)

  • Stays the same everywhere

  • Measured with a balance

Weight

  • Force of gravity acting on an object

  • Measured in newtons (N)

  • Changes depending on gravity

  • Measured with a spring scale

Example

  • Your mass = 50 kg (same on Earth and Moon)

  • Your weight = different (because gravity changes)

Formula for Weight

F = mg

  • F = weight (N)

  • m = mass (kg)

  • g = gravitational field strength

    • Earth: 9.8 N/kg (≈ 10 N/kg)

Example

A boy has a mass of 40 kg. What is his weight?
F = mg
F = 40 × 10
F = 400 N

2. Unit Conversions

  • 1 kg = 1000 g

  • 1 g = 0.001 kg

  • 1 Mg = 1 000 000 g

  • 1 g = 0.000001 Mg

Tips

  • kg → g = ×1000

  • g → kg = ÷1000

  • g → Mg = ÷1 000 000

  • Mg → g = ×1 000 000

3. MagnetismMagnetic vs Non-Magnetic Materials

  • Magnetic: iron, steel, nickel, cobalt

  • Non-magnetic: plastic, wood, glass

Uses of Magnets

  • Fridges

  • Compasses

  • Electric motors

  • Speakers

Magnetic Poles

  • North pole (N)

  • South pole (S)

Rule

  • Like poles repel (N–N, S–S)

  • Unlike poles attract (N–S)

Magnetic Fields

  • Area around a magnet where force is felt

  • Represented by field lines

Field Line Rules

  • Go from North → South

  • Never cross

  • Closer lines = stronger field

4. ElectrostaticsWhat is electrostatics?

  • Study of charges at rest

Types of Charges

  • Positive (+)

  • Negative (−)

Rule

  • Like charges repel

  • Unlike charges attract

Charging by Friction

  • When two objects are rubbed together

  • Electrons move from one object to another

  • One becomes negative, the other positive

Example

  • Rub a balloon on your hair → it sticks to the wall

Interaction of Charges

  • Positive + Positive → repel

  • Negative + Negative → repel

  • Positive + Negative → attract

5. Polarisation (NEW)What is polarisation?

  • Polarisation happens when charges in a neutral object rearrange due to a nearby charged object.

How it works

  • A charged object is brought near a neutral object

  • Charges inside the neutral object shift:

    • Opposite charges move closer

    • Like charges move further away

Important

  • The object is still neutral overall

  • It just has separated charges

Example

  • A charged balloon brought near small paper pieces → they move towards it

  • This is because of polarisation