Forces- physics

• Scalar quantity

  • A quantity that only has a magnitude
  • A quantity that isn't direction dependent
• Vector quantity

  A quantity that has both a magnitude and an associated direction
• Categories of forces

  • Contact forces (objects touching)
  • Non-contact forces (objects separated)
• Examples of vector quantities

  • Velocity
  • Displacement
  • Force
• Examples of non-contact forces

  • Gravitational forces
  • Electrostatic forces
  • Magnetic forces
• Examples of contact forces


  • Friction
  • Air resistance
  • Tension
• How can a vector quantity be drawn and what does it show?

  1. As an arrow

  2. The length of the arrow represents the magnitude

  3. The arrow points in the associated direction
• The unit used for gravitational field strength is N/kg
• Scalar quantities

  • Temperature
  • Time
  • Mass
• The unit used for weight is the Newton (N)
• The name given to the single force that is equivalent to all the other forces acting on a given object is the resultant force
• Weight is the force that acts on an object due to gravity and the object’s mass
• An object’s centre of mass is the single point where an object’s weight can be considered to act through
• Vector quantities

  • Velocity
  • Displacement
  • Force
• The piece of equipment used to measure an object’s weight is a calibrated spring-balance or newton-meter
• Units for work done calculation

  • Work done (Joules), Force (Newtons), Distance (metres)
• Work done = Force x Distance
• The force causes an object to be displaced through a distance
• It must be the distance that is moved along the line of action of the force
• When a force of 1 Newton causes a displacement of 1 metre
• 1 Newton-metre is equal to 1 joule of energy
• 1 Nm = 1 J
• Reasons why air resistance slows down a projectile

  • The object does work against the air resistance
  • Kinetic energy is converted into heat, slowing down the object
• Occurrences when work is done against frictional forces

  • A rise in temperature of the object occurs
  • Kinetic energy is converted to heat
• Alternative name for the turning effect of a force is a moment
• Distance measurement used when calculating a moment is the perpendicular distance from the pivot to the line of action of the force
• Parts of a lever system

  • Load
  • Effort
  • Pivot
• Equation used to calculate the moment of a force: Moment of force = Force x Distance. Units: Moment (Nm), Force (N), Distance (m)
• If an object is in equilibrium, the clockwise moments are equal to the anticlockwise moments
• A lever can be used as a force multiplier
• Example of using a lever to multiply a force

  • A wrench, which has a long handle so that the force applied by the user is multiplied
• When a larger gear is driven by a smaller gear, the larger wheel will rotate more slowly but will also produce a larger moment
• A lever can be used as a force multiplier by
• Three parts of a lever system

  • Load
  • Effort
  • Pivot
• Forces due to pressure in any fluid act at right angles (normal to) the surface
• The Earth’s atmosphere is a thin layer of gas surrounding the Earth
• Units for Pressure equation

  • Pressure (Pascals), Force (Newtons), Area (metre²)
• Pressure = Force/Area
• The density of the atmosphere decreases as altitude increases
• Explanation for pressure increase in fluids with depth

  1. As the depth increases, the mass of liquid above that depth also increases

  2. This means that the force due to the mass increases

  3. Since the force has increased whilst the area has remained constant, the pressure will increase