G2G3 Science C9: Forces & Energy

• These notes pertain to G2G3 Science, specifically focusing on C9: Application of Forces & Transfer of Energy
• These notes were revised on December 23, 2024.

Content Overview

• Forces
• Mass and Weight
• Pressure
• Turning effect of a force
• Energy

Learning Outcomes in Detail

• Force: Defined as a push or a pull
  • Its SI unit is the newton (N).
• Effects of Force on an Object:
  • It can alter the state of rest or motion
  • It is able to modify the size and/or shape
  • It can cause turning effects (e.g., using spanners or levers)
  • It can exert pressure
• Types of Forces: Classified as contact (e.g., friction) and non-contact (e.g., magnetic, gravitational, electrostatic)
• Friction:
  • It opposes relative motion between surfaces.
  • It has both positive and negative effects.
• Reducing Friction
  • Use lubricants, ball bearings, wheels, or polishing.
• Resultant Force: Calculation involves net parallel forces acting on an object.
• Measurement of Force
  • Spring balance (force meter or Newton meter) measures force magnitude.
• Natural Forces
  • Natural destructive forces include earthquakes, tsunamis, volcanic eruptions, and tropical cyclones.
• Mass
• Mass is the measure of the amount of substance,
• Its SI unit is the kilogram (kg).
• Gravitational Field:
  • A region where a mass experiences gravitational attraction.
• Gravitational Field Strength:
  • It is the gravitational force per unit mass, approximately 10 N/kg on Earth.
• Weight Calculation:
  • Weight = mass × gravitational field strength
• Pressure:
• Defined as force per unit area
• The formula is pressure = force/area
• Pressure Application & Appreciation:
  • Relate pressure to force and contact area in daily life (e.g., high-heeled shoes).
  • Atmospheric pressure (e.g., suction cups) and pressure in liquids (e.g., submarines).
• Moment of Force:
  • Describes a turning effect
  • Clockwise and anticlockwise moments are identifiable
  • Moment = force × perpendicular distance from the pivot
• Work & Energy:
• SI unit is the joule (J)
• Forms of Energy:
  • Kinetic, elastic potential, gravitational potential, chemical potential, and thermal.
• Conservation of Energy:
  • Energy cannot be created or destroyed, only transferred or converted
• Energy Conversions: Involve various forms, including energy loss.
• Energy Sources:
  • Include fossil fuels, solar, hydro-electric, wind, geothermal, biofuels, and nuclear
  • Consider their environmental impact (advantages/disadvantages).
• Work: It is done when an object moves in the direction of an applied force.
• Work & Energy Relationship: Energy is transferred when work is done.
• Work Formula: Work done = force × distance moved in the direction of force.

Forces (9.1)

• Force can change the state of rest or the size/shape of an object and exert pressure.
• Friction is a contact force that opposes motion, with both positive and negative effects.
• Ways to reduce friction include lubricants, ball bearings, wheels, and polishing.
• Resultant force is the net force from parallel forces acting on an object.

Tsunamis: The Effects

• Tsunamis are large waves resulting from undersea earthquakes or eruptions.
• Tsunami impact varies from unnoticeable to devastating, depending on the seismic event's characteristics.
• Small tsunamis are common and often appear as strong tides
• Large tsunamis can exceed 30m in height, causing property damage and loss of life.

Measurement of Force

• Spring balance (or Newton meter) measures magnitude of a force, with the newton (N) as its SI unit.

Types of Forces

• Contact Forces require objects to touch (e.g., friction)
• Non-Contact Forces act without touching (e.g., electrostatic, magnetic, gravitational).

Electrostatic Force (3.2)

• It is the force due to attraction and repulsion of charges
• Unlike charges attract, and like charges repel.

Magnetic Force (3.3)

• Magnets exert magnetic force on certain materials
• Unlike poles attract; like poles repel.

Gravitational Force (3.4)

• Planets attract objects due to gravitational force
• Ocean tides are affected by the moon's gravitational pull.

Effects of Forces (4)

• Forces can alter an object’s state of rest/motion, size/shape and exert pressure
• Force applied to a spanner can cause a turning effect

Forces Acting on an Object (5)

• Resultant force (net force) indicates movement direction using double arrowheads.

Mass and Weight (9.2)

• Mass indicates the amount of matter in a body, measured in kilograms (kg).
• Gravitational field is where mass experiences gravitational attraction.
• Gravitational field strength (g) on Earth is approximately 10 N/kg.
• The formula is weight = mass × gravitational field strength.
• Mass is amount of matter, SI unit is kilogram (kg)
• Gravitational field is a region in which a mass experiences a gravity
• Gravitational field strength is the gravitational force per unit mass.
• Weight (W) is gravitational pull on an object; its SI unit is the newton (N).
• Weight is calculated using W = mg.
• Mass is the amount of matter of an object
• Weight is the gravitational force acting on the object.

Pressure (9.3)

• Pressure is force per unit area; measured in pascals (Pa or N/m²).
• The formula is P = F/A, and contact area affects the pressure exerted on an object.
• It is the amount of force applied on a certain area
• Pressure is force/area
• SI unit of pressure is Pascal (Pa) or N/m^2
• Relate pressure to daily life phenomena (ex. high heels cut easier due to higher pressure)

Turning Effect of a Force (9.4)

• A moment causes a turning effect
• Clockwise and anticlockwise moments can be identified.
• A moment is force times perpendicular distance from pivot.
• It's impacted by 2 factors - size of the force and perpendicular distance between force and pivot
• SI unit Newton meter (NM)

Energy (9.5)

• Energy sources include fossil fuels, solar, hydro-electric, and nuclear.
• Note the advantages and disadvantages of different energy sources related to the environment.
• Potential energy is stored.
• It can be elastic, gravitational, or chemical.
• Kinetic energy is movement based.
• Law of conservation of energy is energy cannot be created or destroyed
• Fossil fuels, solar, hydro-electric, wind energy, geothermal energy, biofuels and nuclear energy are energy resources
• Fossil fuels cause pollution while renewable sources of energy are better for the earth

Work Done

• It is the product of the force and the distance moved in the direction of the force
• Measured in Joules (J)
• Note distance moved in the direction of the force must be parallel.
• Energy fuels capability to do work
• Work = force X distance