Forces, Motion and Electricity

• Physics Revision (Dated 6/3/25)

Forces and Motion - Moment

• Every body has a balance point (pivot).
• Moment is equal to force multiplied by distance.
• M = F x S, where M is moment, F is force, and S is distance.
• The unit of moment is Newton meters (Nm).
• Moment is the force multiplied by the distance at the pivot.
• A body can only be balanced if both sides have equal moment.
• Principle of moment: Clockwise moment equals anticlockwise moment.
• Hooke's Law: Relates force to extension
• Graph plotting: F is proportional to x (extension)
• F = -kx, the negative sign is due to opposite force known as restoring force.

Electricity

• Electric current is the rate of flow of electrons or charged particles.
• Current (I) = Charge (Q) / Time (T).
• Units:
• Current is measured in Ampere (Amps/A).
• Charge is measured in Coulombs (C).
• Voltage = Energy/Charge or Voltage = Work/Charge.
• Voltage is the amount of energy in a charged particle.
• Voltage is also the amount of work done by a charged particle.
• Units:
• Voltage is measured in Volts (V).
• Work or energy is measured in Joules (J).
• Charge is measured in Coulombs (C).
• Ohm's Law: Current is directly proportional to voltage, keeping physical conditions like pressure, volume, and temperature constant.
• Power is the product of voltage and current.
• Symbol of power is P.
• The unit of power is Watts (W).
• Formula of electric power: Voltage x Current, or P = V x I.
• Electrical energy: Product of power and time.
• Symbol of energy is E.
• Unit of energy is Joules (J).
• Formula of energy: Power x Time.
• Current is equal to charge multiplied by time.
• Electrical components: Light Dependent Resistor (LDR).
• In condition 1, light is directly proportional to resistance. As light intensity increases, resistance also increases.
• In condition 2, light is inversely proportional to resistance. As light intensity increases, resistance decreases.