Topic 9 – Forces and their effects

• how objects can interact a at a distance without contact,: Gravitational Fields

  -Objects can interact without physically touching each other through fields. The three main types of fields that cause this interaction are:

  Gravitational Fields:

  -acts at a distance and pulls objects towards each other (attract) -Example: The Earth and the Moon interact through gravity. The Earth pulls the Moon towards it, and the Moon's gravity also affects the Earth, causing tides.
• how objects can interact a at a distance without contact: Electrostatic Fields

  -arise from electric charges. Objects with opposite charges attract each other, and objects with like charges repel each other

  -If you rub a balloon on your hair, it becomes negatively charged, and when you bring it close to a wall, the wall is attracted to the balloon due to the electrostatic force.
• how objects can interact a at a distance without contact: Magnetic Fields


  -act between magnetic materials or between a magnet and a moving electric charge.

  -Magnetic forces also operate without direct contact.

  -Example: A magnet can attract or repel another magnet through its magnetic field. A compass needle aligns with the Earth's magnetic field, indicating the direction of Earth's magnetic forces without touching the Earth.
• How objects interact by normal contactforce

  Normal Contact Force:

  • This is the force exerted by a surface to support the weight of an object resting on it. It acts perpendicular (normal) to the surface.
  • Example: When a book is resting on a table, the table exerts an upward normal force that balances the weight of the book, preventing it from falling through the table.
• Objects interacting by contact: Friction

  Friction:

  • Friction is a force that opposes the motion or attempted motion between two surfaces in contact. There are two main types of friction: static friction (when the object is stationary) and kinetic friction (when the object is moving).
  • Example: When you push a box across the floor, friction between the box and the floor resists the motion, making it harder to push.
• Objects interacting by pairs of forces represented as vectors

  -According to Newton's Third Law of Motion, when two objects interact, they exert equal and opposite forces on each other.

  -Gravity is a force that occurs between any 2 objects that have mass.

  -Example: the moon stays in orbit around the earth because the 2 bodies are attracting each other. The force from the moon to earth is the same as the force from the earth to the moon but in opposite directions.
• Objects interacting by pairs of forces represented as vectors(2)


  -These gravitational forces between 2 objects with mass can be represented as vectors.

  • These 2 forces are action-reaction forces.
  • Action-reaction = pairs of forces acting on different objects, in opposite directions.
• -Vector quantities

  -has magnitude and direction

  -Displacement, Velocity, Force, Acceleration, Momentum, weight
• Scalar quantities

  -Only has magnitude

  -Distance, speed, mass, temperature, energy, time, work, power
• Free Body Diagrams

  -When the plane is flying at a constant velocity and height, the horizontal and vertical forces on it are balanced. The reultant force is 0.

  
• Scale diagrams

  -Used to work out resultant force

  -when forces are not always acting along the same line.

  -when plane makes a cross-wind landing, the force from the plane's engine is pushing it forward, but there is also a force from the wind pushing it sideways.

  -IN TEXTBOOK
• -Turning force = momentum

  -$moment\ of\ force\ \left(N\ m\right)\ =$$\ force\left(N\right)\ \times dis\tan ce\ \left(m\right)$

  -

  • Moment of a force (N·m): The rotational effect caused by a force applied to an object. It is measured in Newton meters (N·m).
  • Force (N): The force applied to the object, measured in Newtons (N).
  • Distance (m): The perpendicular distance from the axis of rotation (or pivot point) to the line of action of the force, measured in meters (m).
• When rotational forces are in equilibrium

  -The principle of moments states that when an object is in rotational equilibrium, = Sum of clockwise moments=Sum of anti-clockwise moments
• Lubrication

  Lubrication reduces unwanted energy transfer by decreasing friction between moving parts, which in turn reduces heat generation and wear. It creates a thin layer between surfaces, preventing direct contact and lowering the amount of energy converted into heat. This improves the efficiency of machines, prevents overheating, and extends the lifespan of components. Lubricants also reduce noise, vibration, and corrosion, ensuring smoother operation and reducing energy losses in mechanical systems.
• Levers


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